%%% ====================================================================
%%%  @LaTeX-file{
%%%     filename  = "amstex.dtx",
%%%     version   = "1.2beta",
%%%     date      = "1994/12/13",
%%%     time      = "11:36:57 EST",
%%%     author    = "American Mathematical Society",
%%%     copyright = "Copyright (C) 1994 American Mathematical Society,
%%%                  all rights reserved.  Copying of this file is
%%%                  authorized only if either:
%%%                  (1) you make absolutely no changes to your copy,
%%%                  including name; OR
%%%                  (2) if you do make changes, you first rename it
%%%                  to some other name.",
%%%     address   = "American Mathematical Society,
%%%                  Technical Support,
%%%                  Electronic Products and Services,
%%%                  P. O. Box 6248,
%%%                  Providence, RI 02940,
%%%                  USA",
%%%     telephone = "401-455-4080 or (in the USA and Canada)
%%%                  800-321-4AMS (321-4267)",
%%%     FAX       = "401-331-3842",
%%%     checksum  = "58812 3821 13288 133719",
%%%     email     = "tech-support@math.ams.org (Internet)",
%%%     codetable = "ISO/ASCII",
%%%     keywords  = "latex, amslatex, ams-latex, math, amstex, ams-tex",
%%%     supported = "yes",
%%%     abstract  = "This is part of the AMS-\LaTeX{} distribution. It
%%%                  provides a variety of extra mathematical features,
%%%                  largely derived from AMS-\TeX{}.",
%%%     docstring = "The checksum field above contains a CRC-16 checksum
%%%                  as the first value, followed by the equivalent of
%%%                  the standard UNIX wc (word count) utility output of
%%%                  lines, words, and characters.  This is produced by
%%%                  Robert Solovay's checksum utility.",
%%%  }
%%% ====================================================================
%
%\iffalse
%<*driver>
\documentclass{amsdtx}
\begin{document}
\title{The \pkg{amstex} package}
\author{Frank Mittelbach\and Rainer Sch\"opf\and Michael Downes\and
  David M. Jones}
\date{Version \fileversion, \filedate}
\hDocInput{amstex.dtx}
\end{document}
%</driver>
%\fi
%
% \maketitle
%
% \section{Introduction}
%
%    The \pkg{amstex} package is an adaptation of \fn{amstex.tex} for
%    use as a \latex/ package. For technical and historical notes on the
%    conversion see \fn{amst-hst.tex}. The work was done in 1988--1989
%    by Frank Mittelbach and Rainer Sch\"opf. Some later maintenance
%    work has been done by Michael Downes. David M. Jones added the
%    support for the \opt{fleqn} option in 1994.
%
%^^A% ADD MORE DOCUMENTATION HERE [mjd,2-Sep-1994]
%
% \StopEventually{}
%
%    Standard file identification:
%    \begin{macrocode}
\ProvidesPackage{amstex}[1994/10/27 v1.2beta AMS extra math features]
%    \end{macrocode}
%
% \section{Declare some options}
%
%    The `noamsfonts' option means to avoid declaring math alphabets or
%    symbol fonts for the extra math fonts in the AMSFonts package. If
%    these fonts are declared, it means that the corresponding .tfm
%    files are required even for documents that do not use any symbols
%    from those fonts. So we allow optionally to not declare them, for
%    convenience of users who don't have those fonts declared and don't
%    want to use them.
%
%    But we still load the amsfonts package because it contains some
%    other needed items, eg mathstrut stuff and \cn{big} stuff.
%    \begin{macrocode}
\DeclareOption{noamsfonts}{%
  \PassOptionsToPackage{noamsfonts}{amsfonts}}
%    \end{macrocode}
%    The `psamsfonts' option, passed on the amsfonts package, means that
%    alternative \fn{.fd} files should be used that do not refer to
%    \fn{.tfm} files for sizes 6,8,9 (which are not present in the
%    PostScript AMS fonts set from Y\&Y/Blue Sky Research).
%    \begin{macrocode}
\DeclareOption{psamsfonts}{%
  \PassOptionsToPackage{psamsfonts}{amsfonts}}
%    \end{macrocode}
%
%    Handling of limits on integrals, sums, operatornames.
%    \begin{macrocode}
\DeclareOption{intlimits}{\let\ilimits@\displaylimits}
\DeclareOption{nointlimits}{\let\ilimits@\nolimits}
\DeclareOption{sumlimits}{\let\slimits@\displaylimits}
\DeclareOption{nosumlimits}{\let\slimits@\nolimits}
\DeclareOption{namelimits}{\let\nlimits@\displaylimits}
\DeclareOption{nonamelimits}{\let\nlimits@\nolimits}
%    \end{macrocode}
%    The following two switches might have been defined already by the
%    documentclass, but it doesn't hurt to re-execute the \cs{newif}'s.
%    \begin{macrocode}
\newif\ifctagsplit@
\newif\iftagsleft@
%    \end{macrocode}
%
%    Right or left placement of equation numbers.
%    \begin{macrocode}
\DeclareOption{leqno}{\tagsleft@true}
\DeclareOption{reqno}{\tagsleft@false}
\DeclareOption{centertags}{\ctagsplit@true}
\DeclareOption{tbtags}{\ctagsplit@false}
%    \end{macrocode}
%
%    DMJ: Flushleft equations.
%
%    DMJ: The left margin of math enviroments is controlled by
%    \cs{@mathmargin}.  This can be set to \cs{@centering} to
%    implement the default behaviour, i.e., centered equations, and to
%    something else to implement the flushleft style.
%
%    DMJ: In theory, all that's needed to activate the flushleft mode
%    in the AMS document classes is something like this:
%    \begin{verbatim}
%        \DeclareOption{fleqn}{%
%            \AtBeginDocument{\@mathmargin30pt}%
%        }
%    \end{verbatim}
%    DMJ: (In fact, unless the document class wants to specify the
%    \cs{@mathmargin}, it doesn't need to do anything with the fleqn
%    option.)
%    \begin{macrocode}
\newif\if@fleqn

\newskip\@mathmargin
\@mathmargin\@centering

\DeclareOption{fleqn}{%
    \@fleqntrue
    \@mathmargin = -1sp
    \AtBeginDocument{%
        \ifdim\@mathmargin= -1sp
            \@mathmargin\leftmargini
        \fi
    }%
}
%    \end{macrocode}
%
%    DMJ: This ensures that \cs{@mathmargin} is given some sort of
%    sensible default if the class doesn't specify one, while still
%    allowing a user to override the default value in their document
%    preamble.  (Incidentally, I'm initializing \cs{@mathmargin} to
%    \cs{leftmargini} for compatibility with \fn{fleqn.clo}, but I'm
%    not at all convinced that's the right thing to do.)
%
%    DMJ: The next question is what happens when amstex is used with
%    one of the standard classes.  Unfortunately, \LaTeX\ implements
%    \opt{fleqn} somewhat clumsily; instead of paramaterizing the
%    definitions of the math structures (as I've attempted to do
%    here), \fn{fleqn.clo} declares a dimen \cn{mathindent} that is
%    much like my \cs{@mathmargin} and then redefines \cn\[, \cn\],
%    \cn{equation}, and \cn{eqnarray}.  This means that things could
%    get rather messy in 2.09 compatibility mode, since \fn{fleqn.clo}
%    might be loaded after \fn{amstex.sty}, which could cause a real
%    mess.  (This won't be a problem in 2e native mode, since
%    \fn{amstex}.sty would always be loaded after \fn{fleqn.clo}, so
%    the only question is whether \fn{amstex.sty} should try to make
%    sure that \cs{eqnarray} gets indented by the same amount as all
%    the \AMS\ structures by, for example, saying
%    \verb+\let\mathindent\@mathmargin+.)  I really don't know what to
%    do in compatibility mode, though.  Maybe bind \cn{mathindent} to
%    \cs{@mathmargin} if it's defined and do something like this if
%    it's not:
%    \begin{verbatim}
%        \@ifundefined{mathindent}%
%            {\AtBeginDocument{%
%                \@ifundefined{mathindent}{}%
%                    {warning about loading fleqn.clo after amstex.sty}}%
%            }
%            {\let\mathindent\@mathmargin}
%    \end{verbatim}
%    This would at least detect when \fn{fleqn.clo} is loaded after
%    \fn{amstex.sty}.
%
%
%    \begin{macrocode}
\ExecuteOptions{nointlimits,sumlimits,namelimits}
\ProcessOptions
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \section{Call some other packages}
%
%    \begin{macrocode}
\RequirePackage{amstext}[1994/09/01]     % \text
\RequirePackage{amsfonts}[1994/09/01]    % \newsymbol, msam, msbm, eufm
\RequirePackage{amsbsy}[1994/09/01]      % \boldsymbol
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \section{Miscellaneous}
%
% \begin{macro}{\AmSTeX}
% \begin{macro}{\AmS}
%    The |\AmS| prefix can be used to construct the combination
%    |\AmS-\LaTeX|. We call cmsy directly in lieu of trying to access it
%    through the math fonts setup (e.g. |\the\textfont2|) because math
%    fonts can't be relied on to be properly set up if we are not inside
%    a math formula. This means that if this command is used in a
%    document where CM fonts are not wanted, then a font substitution
%    will need to be declared, e.g.:
% \begin{verbatim}
% \DeclareFontShape{OMS}{cmsy}{m}{n}{ <-> sub * xxx/m/n }{}
% \end{verbatim}
%    where \verb'xxx' is some alternate font family.
%    \begin{macrocode}
\def\AmSTeX{\protect\AmS-\protect\TeX{}}
\def\AmS{{\protect\AmSfont
  A\kern-.1667em\lower.5ex\hbox{M}\kern-.125emS}}
%    \end{macrocode}
%    Taking the first letter of \cs{f@series} will produce |b| or |m|
%    for the most common values (|b,bx,m|). It may produce nonsense for
%    more unusual values of \cs{f@series}, so for safety's sake we have
%    an additional \cs{if} test. We want to avoid setting the series to
%    |bx| because in a standard \latex/ installation the combination
%    |cmsy/bx/n| does not have a font definition, and the user
%    would get a font substitution warning on screen.
%    \begin{macrocode}
\def\AmSfont{%
  \usefont{OMS}{cmsy}{\if\@xp\@car\f@series\@nil bb\else m\fi}{n}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%    We redefine |\prim@s}| and |\pr@m@s| to use |\@let@token| instead
%    of |\next|.
%    \begin{macrocode}
\def\prim@s{\prime\futurelet\@let@token\pr@m@s}
%
\def\pr@m@s{%
  \ifx\@let@token'\DN@##1{\prim@s}\else\let\next@\egroup\fi\next@}
%    \end{macrocode}
%    We redefine |\prime| to add a leading null kern so that something
%    like |^{\mathcal{A}\prime}| will not erroneously cause the skewchar
%    kern for the letter $\mathcal{A}$ to be inserted. (In the original
%    \tex/ font layout for \fn{cmsy10} the prime character serves as the
%    |\skewchar| of the font.) The extra braces allow \verb"^\prime" to
%    work. (Rule of thumb: the user should be allowed to type a `simple
%    symbol' superscript without the braces if they wish.)
%    \begin{macrocode}
\let\@prime=\prime
\renewcommand{\prime}{{\kern\z@\@prime}}
%    \end{macrocode}
%
%    Fill in some gaps in the set of spacing commands, and make them
%    all work equally well in or out of math. Maybe also (or instead?)
%    users should be told how to use |\mkern| or |\mskip| for any
%    unusual spacing in math.
%
%    We want all these commands to be robust but declaring them all
%    with |\DeclareRobustCommand| uses up an control sequence name per
%    command; to avoid this, we define a common command |\mspace|
%    which carries the robustness burden for all of them. The standard
%    |\relax| before the |\ifmmode| is not necessary because of the
%    |\protect| added by |\DeclareRobustCommand|.
%    \begin{macrocode}
\DeclareRobustCommand{\mspace}[3]{%
  \ifmmode\mskip#1#2\else\kern#1#3\fi\relax}
\renewcommand{\,}{\mspace+\thinmuskip{.1667em}}
\let\thinspace\,
\renewcommand{\!}{\mspace-\thinmuskip{.1667em}}
\let\negthinspace\!
\renewcommand{\:}{\mspace+\medmuskip{.2222em}}
\let\medspace\:
\newcommand{\negmedspace}{\mspace-\medmuskip{.2222em}}
\renewcommand{\;}{\mspace+\thickmuskip{.2777em}}
\let\thickspace\;
\newcommand{\negthickspace}{\mspace-\thickmuskip{.2777em}}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\implies{\DOTSB\;\Longrightarrow\;}
\def\impliedby{\DOTSB\;\Longleftarrow\;}
%    \end{macrocode}
%
%    \begin{macrocode}
\begingroup \catcode`\"=12 % in case activated by a preceding package
\gdef\And{\DOTSB\;\mathchar"3026 \;}
%    \end{macrocode}
%
%    Add left/right specific versions of \cn{vert}, \cn{Vert}
%    \begin{macrocode}
\gdef\lvert{\delimiter"426A30C }
\gdef\rvert{\delimiter"526A30C }
\gdef\lVert{\delimiter"426B30D }
\gdef\rVert{\delimiter"526B30D }
\endgroup % restore "
%    \end{macrocode}
%
%    The square-bracket options of \verb+\frac+ and
%    \verb+\fracwithdelims+ replace the commands \verb+\thickfrac+ and
%    \verb+\thickfracwithdelims+ of original \amstex/. For convenient
%    carryover to \cn{dfrac} and \cn{tfrac}, the auxiliary function for
%    \cn{frac} is called \cn{frfrac} (`fragile frac') rather than the
%    usual name for an optional-arg function (\cn{\\frac}).
%    \begin{macrocode}
\DeclareRobustCommand{\frac}{\new@ifnextchar[{\frfrac{}}{\frfrac{}[]}}
\def\frfrac#1[#2]#3#4{\def\next@{#2}%
  \ifx\next@\@empty \def\next@{#1{#3\over#4}}%
  \else \def\next@{#1{#3\above#2\relax#4}}%
  \fi
  \next@}
%    \end{macrocode}
%
%    The [] option for setting the rule width is not
%    currently available with \cn{dfrac} and \cn{tfrac},
%    I don't think that such a thing is needed often enough to justify
%    the extra overhead. [mjd,1994/10/04]
%    \begin{macrocode}
\def\dfrac{\protect\frfrac\displaystyle[]}
\def\tfrac{\protect\frfrac\textstyle[]}
%    \end{macrocode}
%    Like \cn{frac}, \cn{binom} calls an auxiliary function \cn{frbinom}
%    where `fr' stands for `fragile'.
%    \begin{macrocode}
\DeclareRobustCommand{\binom}{\frbinom{}}
\def\frbinom#1#2#3{#1{#2\atopwithdelims()#3}}
\def\dbinom{\protect\frbinom\displaystyle}
\def\tbinom{\protect\frbinom\textstyle}
%    \end{macrocode}
%
%    |\colon| is for a colon in math that resembles a text colon: small
%    space on the left, larger space on the right. The |:| character
%    by itself is treated as a |\mathrel| i.e. large, equal spacing on
%    both sides.
%    \begin{macrocode}
\def\colon{\nobreak\mskip2mu\mathpunct{}\nonscript
  \mkern-\thinmuskip{:}\mskip6muplus1mu\relax}
%    \end{macrocode}
%
%    Default value for sum limits is |\displaylimits|, see option
%    `nosumlimits'.
%
%    We redefine all the cumulative operator symbols to add a |\DOTSB|
%    token in their expansion so that |\dots| can choose the proper
%    alternative if such a symbol follows.
%    \begin{macrocode}
\DeclareMathSymbol{\coprod@}{\mathop}{largesymbols}{"60}
\def\coprod{\DOTSB\coprod@\slimits@}
\DeclareMathSymbol{\bigvee@}{\mathop}{largesymbols}{"57}
\def\bigvee{\DOTSB\bigvee@\slimits@}
\DeclareMathSymbol{\bigwedge@}{\mathop}{largesymbols}{"56}
\def\bigwedge{\DOTSB\bigwedge@\slimits@}
\DeclareMathSymbol{\biguplus@}{\mathop}{largesymbols}{"55}
\def\biguplus{\DOTSB\biguplus@\slimits@}
\DeclareMathSymbol{\bigcap@}{\mathop}{largesymbols}{"54}
\def\bigcap{\DOTSB\bigcap@\slimits@}
\DeclareMathSymbol{\bigcup@}{\mathop}{largesymbols}{"53}
\def\bigcup{\DOTSB\bigcup@\slimits@}
\DeclareMathSymbol{\prod@}{\mathop}{largesymbols}{"51}
\def\prod{\DOTSB\prod@\slimits@}
\DeclareMathSymbol{\sum@}{\mathop}{largesymbols}{"50}
\def\sum{\DOTSB\sum@\slimits@}
\DeclareMathSymbol{\bigotimes@}{\mathop}{largesymbols}{"4E}
\def\bigotimes{\DOTSB\bigotimes@\slimits@}
\DeclareMathSymbol{\bigoplus@}{\mathop}{largesymbols}{"4C}
\def\bigoplus{\DOTSB\bigoplus@\slimits@}
\DeclareMathSymbol{\bigodot@}{\mathop}{largesymbols}{"4A}
\def\bigodot{\DOTSB\bigodot@\slimits@}
\DeclareMathSymbol{\bigsqcup@}{\mathop}{largesymbols}{"46}
\def\bigsqcup{\DOTSB\bigsqcup@\slimits@}
%    \end{macrocode}
%    Triple and quadruple dot accents.
%    \begin{macrocode}
\def\dddot#1{{\mathop{#1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@
 \hbox{\normalfont ...}\vss}}}}
\def\ddddot#1{{\mathop{#1}\limits^{\vbox to-1.4\ex@{\kern-\tw@\ex@
 \hbox{\normalfont....}\vss}}}}
%    \end{macrocode}
%
%    Change the definition of \verb"~" to automatically remove a
%    preceding space as well as a following space, if present.
%    \begin{macrocode}
\def~{\nobreakspace}
\DeclareRobustCommand{\nobreakspace}{\unskip\nobreak\ \ignorespaces}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \section{Integral signs}
%
%    The straightforward |\ifinner| test to see if the current math
%    context is non-display, fails if, for instance, we are typesetting
%    a multiline display within an |\halign|, with the pieces going
%    into constructions like
%    \begin{verbatim}
%    $\displaystyle...$
%    \end{verbatim}
%    So we need a better test to find out if we are `in a display'. We
%    therefore create |\if@display|.
%
%    \begin{macrocode}
\newif\if@display
\everydisplay\expandafter{\the\everydisplay \@displaytrue}
%    \end{macrocode}
%
%    Default value for integral limits is |\nolimits|, see the
%    definition of the `nointlimits' option.
%    \begin{macrocode}
\def\int{\DOTSI\intop\ilimits@}
\def\oint{\DOTSI\ointop\ilimits@}
\def\intkern@{\mkern-6mu\mathchoice{\mkern-3mu}{}{}{}}
\def\intdots@{\mathchoice{\@cdots}%
 {{\cdotp}\mkern1.5mu{\cdotp}\mkern1.5mu{\cdotp}}%
 {{\cdotp}\mkern1mu{\cdotp}\mkern1mu{\cdotp}}%
 {{\cdotp}\mkern1mu{\cdotp}\mkern1mu{\cdotp}}}

\def\iint{\DOTSI\protect\ints@\tw@}
\def\iiint{\DOTSI\protect\ints@\thr@@}
\def\iiiint{\DOTSI\protect\ints@{4}}
\def\idotsint{\DOTSI\protect\ints@\z@}

%    #1 = multiplicity
\def\ints@#1{%
  \mkern-7mu\mathchoice{\mkern-2mu}{}{}{}%
  \mathop{\mkern7mu\mathchoice{\mkern2mu}{}{}{}%
    \intop\ifnum#1=\z@\intdots@
    \else\intkern@\fi
    \ifnum#1>\tw@\intop\intkern@\fi
    \ifnum#1>\thr@@\intop\intkern@\fi
    \intop
  }\ilimits@
}
%    \end{macrocode}
%
%    The definition of \verb+\nolimits@+ shows a standard \AmSTeX{}
%    construction.  We want to find out what the next token is going
%    to be, so we use \verb+\futurelet\@let@token\next@+; the
%    \verb+\@let@token+ is assigned the value of the next token and
%    then we must define \verb+\next@+ to look at \verb+\@let@token+
%    and decide what to do. We could name \verb+\next@+ to be
%    \verb+\nolimits@@+ or something, but by always using
%    \verb+\next@+ in similar constructions we cut down on the number
%    of control sequence names that we use. But this means that
%    \verb+\nolimits@+ must incorporate the appropriate definition of
%    \verb+\next@+.  Notice that \verb+\next@+ turns around and
%    redefines itself again; once more this is to save a control
%    sequence name.
%
%    What \verb+\nolimits@+ does is keep a \verb+\limits+ typed by the
%    user from having any effect. This is used for operatornames whose
%    standard usage is never to have limits.
%    \begin{macrocode}
\def\nolimits@{%
  \DN@{\nolimits\ifx\@let@token\limits\expandafter\@gobble\fi}%
  \FN@\next@}
%    \end{macrocode}
%
%    In operator names, it is sometimes desired to have text-mode
%    punctuation such as |'| |*| |-| |/| |:|. Because the body of an
%    operator name is set in math mode, these few punctuation
%    characters will not come out right (wrong symbol/and or wrong
%    spacing). The purpose of |\newmcodes@| is to make them act like
%    their normal text versions.
%
%    Where practical, we use decimal numbers to cut down main mem
%    usage (|"| not needed).
%    \begin{macrocode}
\begingroup \catcode`\"=12
\gdef\newmcodes@{\mathcode`\'39\mathcode`\*42\mathcode`\."613A%
 \mathcode`\-45\mathcode`\/47\mathcode`\:"603A\relax}
\endgroup
%    \end{macrocode}
%
%    The command |\operatorname| prints its argument as a `math
%    operator' like |\sin| or |\det|, with proper font and spacing.
%    \begin{macrocode}
\DeclareRobustCommand{\operatorname}{%
  \@ifstar{\qopname\newmcodes@ n}%
          {\qopname\newmcodes@{no}}}%
\DeclareRobustCommand{\qopname}[3]{\mathop{#1\operator@font#3}%
  \csname #2limits@\endcsname}
\def\arccos{\qopname\relax{no}{arccos}}
\def\arcsin{\qopname\relax{no}{arcsin}}
\def\arctan{\qopname\relax{no}{arctan}}
\def\arg{\qopname\relax{no}{arg}}
\def\cos{\qopname\relax{no}{cos}}
\def\cosh{\qopname\relax{no}{cosh}}
\def\cot{\qopname\relax{no}{cot}}
\def\coth{\qopname\relax{no}{coth}}
\def\csc{\qopname\relax{no}{csc}}
\def\deg{\qopname\relax{no}{deg}}
\def\det{\qopname\relax n{det}}
\def\dim{\qopname\relax{no}{dim}}
\def\exp{\qopname\relax{no}{exp}}
\def\gcd{\qopname\relax n{gcd}}
\def\hom{\qopname\relax{no}{hom}}
\def\inf{\qopname\relax n{inf}}
\def\injlim{\qopname\relax n{inj\,lim}}
\def\ker{\qopname\relax{no}{ker}}
\def\lg{\qopname\relax{no}{lg}}
\def\lim{\qopname\relax n{lim}}
\def\liminf{\qopname\relax n{lim\,inf}}
\def\limsup{\qopname\relax n{lim\,sup}}
\def\ln{\qopname\relax{no}{ln}}
\def\log{\qopname\relax{no}{log}}
\def\max{\qopname\relax n{max}}
\def\min{\qopname\relax n{min}}
\def\Pr{\qopname\relax n{Pr}}
\def\projlim{\qopname\relax n{proj\,lim}}
\def\sec{\qopname\relax{no}{sec}}
\def\sin{\qopname\relax{no}{sin}}
\def\sinh{\qopname\relax{no}{sinh}}
\def\sup{\qopname\relax n{sup}}
\def\tan{\qopname\relax{no}{tan}}
\def\tanh{\qopname\relax{no}{tanh}}
%    \end{macrocode}
%
% \begin{macro}{\operator@font}
%    This command is provided to allow the document styles to decide in
%    which way math operators like `max' or `log' are typeset. The
%    default is to set them in \meta{math group} zero of the current
%    math version.
%    \begin{macrocode}
\def\operator@font{\mathgroup\symoperators}
%    \end{macrocode}
% \end{macro}
%
%    For backwards compatibility we keep this old command name for the
%    time being:
%    \begin{macrocode}
\def\operatornamewithlimits{\operatorname*}
%    \end{macrocode}
%
%     These macros use \verb+\mathpalette+s
%     so that they will change size in script and scriptscript styles,
%     though it's hard to imagine they will ever be used there (the
%     arrows, particularly, look bad in subscript sizes).
%     Notice that the use of \verb+\ex@+ means that the vertical spacing
%     may not be optimal in script and scriptscript sizes.
%     Unfortunately \tex/ provides no easy way to do math mode
%     vertical spacing that varies with current math style like mu
%     units.
%    \begin{macrocode}
\def\varlim@#1#2{\mathop{\vtop{\ialign{##\crcr
 \hfil$#1\m@th\operator@font lim$\hfil\crcr
 \noalign{\nointerlineskip\kern\ex@}#2#1\crcr
 \noalign{\nointerlineskip\kern-\ex@}\crcr}}}}
\def\varinjlim{\mathpalette\varlim@\rightarrowfill@}
\def\varprojlim{\mathpalette\varlim@\leftarrowfill@}
\def\varliminf{\mathpalette\varliminf@{}}
\def\varliminf@#1{\mathop{\@@underline{\vrule\@depth.2\ex@\@width\z@
   \hbox{$#1\m@th\operator@font lim$}}}}
\def\varlimsup{\mathpalette\varlimsup@{}}
\def\varlimsup@#1{\mathop{\@@overline
  {\hbox{$#1\m@th\operator@font lim$}}}}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \section{Equation numbering}
%     Provide a convenient way to specify that equations should be
%     numbered within sections.
%    \begin{macrocode}
\def\numberwithin#1#2{\@ifundefined{c@#1}{\@nocounterr{#1}}{%
  \@ifundefined{c@#2}{\@nocnterr{#2}}{%
  \@addtoreset{#1}{#2}%
  \toks@\expandafter\expandafter\expandafter{\csname the#1\endcsname}%
  \expandafter\xdef\csname the#1\endcsname
    {\expandafter\noexpand\csname the#2\endcsname
     .\the\toks@}}}}
%    \end{macrocode}
%
%    To make references to equation numbers easier, we provide
%    \cw{eqref}.  We almost don't need \cw{textup}, except that
%    \cw{tagform@} doesn't supply the italic correction.
%    \begin{macrocode}
\def\eqref#1{\textup{\tagform@{\ref{#1}}}}
%    \end{macrocode}
%
%    The commands |\bmod|, |\pmod|, |\pod|, |\mod| aren't currently
%    robust. [mjd,5-Sep-1994]
%    \begin{macrocode}
\def\bmod{\mskip-\medmuskip\mkern5mu\mathbin
  {\operator@font mod}\penalty900
  \mkern5mu\mskip-\medmuskip}
\def\pod#1{\allowbreak\if@display\mkern18mu\else\mkern8mu\fi(#1)}
\def\pmod#1{\pod{{\operator@font mod}\mkern6mu#1}}
\def\mod#1{\allowbreak\if@display\mkern18mu
  \else\mkern12mu\fi{\operator@font mod}\,\,#1}
%    \end{macrocode}
%
%     Continued fractions. The optional arg l or r controls horizontal
%     placement of the numerators.
%     The \verb+\kern-\nulldelimiterspace+ is needed in the definition
%     if we want the right-hand sides of the fraction rules to line
%     up.  The \verb+\strut+ keeps the numerator of a subsidiary cfrac
%     from coming too close to the fraction rule above it.
%
%    \begin{macrocode}
\newcommand{\cfrac}[3][c]{{\displaystyle\frac{%
  \strut\ifx r#1\hfill\fi#2\ifx l#1\hfill\fi}{#3}}%
  \kern-\nulldelimiterspace}
%    \end{macrocode}
%    Old command names \cn{lcfrac}, \cn{rcfrac} are retained for the
%    time being.
%    \begin{macrocode}
\def\lcfrac{\@subst@obsolete\lcfrac{\cfrac[l]}}
\def\rcfrac{\@subst@obsolete\rcfrac{\cfrac[r]}}
%    \end{macrocode}
%
%    |\overset| and |\underset| put symbols above, respectively below,
%    a symbol that is not a |\mathop| and therefore does not naturally
%    accept limits. |\binrel@@| uses information collected by
%    |\binrel@| to make the resulting construction be of type mathrel
%    or mathbin if the base symbol is either of those types.
%    \begin{macrocode}
\def\overset#1#2{\binrel@{#2}%
  \binrel@@{\mathop{\kern\z@#2}\limits^{#1}}}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\underset#1#2{\binrel@{#2}%
  \binrel@@{\mathop{\kern\z@#2}\limits_{#1}}}
%    \end{macrocode}
%
%    |\sideset| allows placing
%    `adscript' symbols at the four corners of a |\mathop|, \emph{in
%    addition to} limits. Left-side adscripts go into arg |#1|, in the
%    form |_{...}^{...}|, and right-side adscripts go into arg |#2|.
%    \begin{macrocode}
\def\sideset#1#2#3{%
  \setbox\z@\hbox{$\displaystyle{\vphantom{#3}}#1{#3}\m@th$}%
  \setbox\tw@\hbox{$\displaystyle{#3}#2\m@th$}%
  \hskip\wd\z@\hskip-\wd\tw@\mathop{\hskip\wd\tw@\hskip-\wd\z@
  {\vphantom{#3}}#1{#3}#2}}
%    \end{macrocode}
%
% \begin{macro}{\smash}
%    We add to the \verb+\smash+ command an optional argument
%    denoting the part of the formula to be smashed.
%    \begin{macrocode}
\renewcommand{\smash}[2][tb]{%
%    \end{macrocode}
%    Here we save the value of the optional argument in \verb+\smash@+
%    for later use in \verb+\finsm@sh+.
%    \begin{macrocode}
  \def\smash@{#1}%
  \ifmmode\expandafter\mathpalette\expandafter\mathsm@sh\else
        \expandafter\makesm@sh\fi{#2}}
%    \end{macrocode}
%    When we come to this part of the code \verb+\mathsm@sh+ or
%    \verb+\makesm@sh+ have stored their argument in box zero.
%    Depending on the letters stored in \verb+\smash@+ we reset either
%    the height, depth or both of box zero.
%    \begin{macrocode}
\def\finsm@sh{\def\mb@t{\ht\z@\z@}\def\mb@b{\dp\z@\z@}%
  \def\mb@tb{\mb@t\mb@b}%
  {\csname mb@\smash@\endcsname}%
  \leavevmode\boxz@}
%    \end{macrocode}
% \end{macro}
%
%    The minus sign used in constructing these arrow fills is smashed
%    so that superscripts above the arrows won't be too high. This
%    primarily affects the \verb|@>>>| and \verb|@<<<| arrows.
%
%    Only the height of the minus sign box is set to 0 because the
%    depth is not any greater than the depth of the arrowheads it will
%    be used with.
%    \begin{macrocode}
\def\rightarrowfill@#1{\m@th\setboxz@h{$#1-$}\ht\z@\z@
  $#1\copy\z@\mkern-6mu\cleaders
  \hbox{$#1\mkern-2mu\box\z@\mkern-2mu$}\hfill
  \mkern-6mu\mathord\rightarrow$}
\def\leftarrowfill@#1{\m@th\setboxz@h{$#1-$}\ht\z@\z@
  $#1\mathord\leftarrow\mkern-6mu\cleaders
  \hbox{$#1\mkern-2mu\copy\z@\mkern-2mu$}\hfill
  \mkern-6mu\box\z@$}
\def\leftrightarrowfill@#1{\m@th\setboxz@h{$#1-$}\ht\z@\z@
  $#1\mathord\leftarrow\mkern-6mu\cleaders
  \hbox{$#1\mkern-2mu\box\z@\mkern-2mu$}\hfill
  \mkern-6mu\mathord\rightarrow$}
%
\def\overarrow@#1#2#3{\vbox{\ialign{##\crcr#1#2\crcr
 \noalign{\kern-\ex@\nointerlineskip}$\m@th\hfil#2#3\hfil$\crcr}}}
\def\overrightarrow{\mathpalette{\overarrow@\rightarrowfill@}}
\def\overleftarrow{\mathpalette{\overarrow@\leftarrowfill@}}
\def\overleftrightarrow{\mathpalette{\overarrow@\leftrightarrowfill@}}
%
\def\underarrow@#1#2#3{%
 \vtop{\ialign{##\crcr$\m@th\hfil#2#3\hfil$\crcr
 \noalign{\nointerlineskip\kern-.5\ex@}#1#2\crcr}}}
\def\underrightarrow{\mathpalette{\underarrow@\rightarrowfill@}}
\def\underleftarrow{\mathpalette{\underarrow@\leftarrowfill@}}
\def\underleftrightarrow{\mathpalette{\underarrow@\leftrightarrowfill@}}
%    \end{macrocode}
%
%    We can't use \verb|\newif| for \verb|\ifgtest@| because we want
%    to include \verb|\global| in the definitions of
%    \verb|\gtest@true| and \verb|\gtest@false|.
%    \begin{macrocode}
\let\ifgtest@\iffalse                              % initial value
\def\gtest@true{\global\let\ifgtest@\iftrue}
\def\gtest@false{\global\let\ifgtest@\iffalse}
\let\DOTSI\relax
\let\DOTSB\relax
\let\DOTSX\relax
{\uccode`7=`\\ \uccode`8=`m \uccode`9=`a \uccode`0=`t \uccode`!=`h
 \uppercase{%
  \gdef\math@#1#2#3#4#5#6\math@{\gtest@false\ifx 7#1\ifx 8#2%
  \ifx 9#3\ifx 0#4\ifx !#5\xdef\meaning@{#6}\gtest@true
  \fi\fi\fi\fi\fi}}}
{\uccode`7=`c \uccode`8=`h \uccode`9=`\"
 \uppercase{\gdef\mathch@#1#2#3#4#5#6\mathch@{\gtest@false
  \ifx 7#1\ifx 8#2\ifx 9#5\gtest@true\xdef\meaning@{9#6}\fi\fi\fi}}}
\newcount\classnum@
\def\getmathch@#1.#2\getmathch@{\classnum@#1 \divide\classnum@4096
 \ifcase\number\classnum@\or\or\gdef\thedots@{\dotsb@}\or
 \gdef\thedots@{\dotsb@}\fi}
{\uccode`4=`b \uccode`5=`i \uccode`6=`n
 \uppercase{\gdef\mathbin@#1#2#3{\relaxnext@
  \def\nextii@##1\mathbin@{\ifx\@sptoken\@let@token\gtest@true\fi}%
  \gtest@false\DN@##1\mathbin@{}%
 \ifx 4#1\ifx 5#2\ifx 6#3\DN@{\FN@\nextii@}\fi\fi\fi\next@}}}
{\uccode`4=`r \uccode`5=`e \uccode`6=`l
 \uppercase{\gdef\mathrel@#1#2#3{\relaxnext@
  \def\nextii@##1\mathrel@{\ifx\@sptoken\@let@token\gtest@true\fi}%
 \gtest@false\DN@##1\mathrel@{}%
 \ifx 4#1\ifx 5#2\ifx 6#3\DN@{\FN@\nextii@}\fi\fi\fi\next@}}}
{\uccode`5=`m \uccode`6=`a \uccode`7=`c
 \uppercase{\gdef\macro@#1#2#3#4\macro@{\gtest@false
  \ifx 5#1\ifx 6#2\ifx 7#3\gtest@true
  \xdef\meaning@{\macro@@#4\macro@@}\fi\fi\fi}}}
\def\macro@@#1->#2\macro@@{#2}
\newcount\DOTSCASE@
{\uccode`6=`\\ \uccode`7=`D \uccode`8=`O \uccode`9=`T \uccode`0=`S
 \uppercase{\gdef\DOTS@#1#2#3#4#5{\gtest@false\DN@##1\DOTS@{}%
  \ifx 6#1\ifx 7#2\ifx 8#3\ifx 9#4\ifx 0#5\let\next@\DOTS@@
  \fi\fi\fi\fi\fi
  \next@}}}
{\uccode`3=`B \uccode`4=`I \uccode`5=`X
 \uppercase{\gdef\DOTS@@#1{\relaxnext@
  \def\nextii@##1\DOTS@{\ifx\@sptoken\@let@token\gtest@true\fi}%
  \DN@{\FN@\nextii@}%
  \ifx 3#1\global\DOTSCASE@\z@\else
  \ifx 4#1\global\DOTSCASE@\@ne\else
  \ifx 5#1\global\DOTSCASE@\tw@\else\DN@##1\DOTS@{}%
  \fi\fi\fi\next@}}}
{\uccode`5=`\\ \uccode`6=`n \uccode`7=`o \uccode`8=`t
 \uppercase{\gdef\not@#1#2#3#4{\relaxnext@
  \def\nextii@##1\not@{\ifx\@sptoken\@let@token\gtest@true\fi}%
 \gtest@false\DN@##1\not@{}%
 \ifx 5#1\ifx 6#2\ifx 7#3\ifx 8#4\DN@{\FN@\nextii@}\fi\fi\fi
 \fi\next@}}}
\def\keybin@{\gtest@true
 \ifx\@let@token+\else\ifx\@let@token=\else\ifx\@let@token<\else\ifx\@let@token>\else
 \ifx\@let@token-\else
 \ifx\@let@token*\else\ifx\@let@token:\else\gtest@false\fi\fi\fi\fi\fi\fi\fi}
\DeclareRobustCommand{\dots}{\relax
  \csname\ifmmode m\else t\fi dots@\endcsname}
\def\tdots@{\leavevmode\unskip\relaxnext@
 \DN@{$\m@th\@ldots\,
   \ifx\@let@token,\,$\else\ifx\@let@token.\,$\else\ifx\@let@token;\,$\else
   \ifx\@let@token:\,$\else
   \ifx\@let@token?\,$\else\ifx\@let@token!\,$\else$ \fi\fi\fi\fi\fi\fi}%
 \ \FN@\next@}
\def\mdots@{\FN@\mdots@@}
\def\mdots@@{\gdef\thedots@{\dotso@}%
 \ifx\@let@token\boldsymbol\gdef\thedots@\boldsymbol{\boldsymboldots@}\else
 \ifx,\@let@token\gdef\thedots@{\dotsc}%
 \else\ifx\not\@let@token\gdef\thedots@{\dotsb@}%
 \else\keybin@
 \ifgtest@\gdef\thedots@{\dotsb@}%
 \else\xdef\meaning@{\meaning\@let@token..........}\xdef\meaning@@{\meaning@}%
  \expandafter\math@\meaning@\math@
  \ifgtest@
   \expandafter\mathch@\meaning@\mathch@
   \ifgtest@\expandafter\getmathch@\meaning@\getmathch@\fi
  \else\expandafter\macro@\meaning@@\macro@
  \ifgtest@
   \expandafter\not@\meaning@\not@\ifgtest@\gdef\thedots@{\dotsb@}%
  \else\expandafter\DOTS@\meaning@\DOTS@
  \ifgtest@
   \ifcase\number\DOTSCASE@\gdef\thedots@{\dotsb@}%
    \or\gdef\thedots@{\dotsi}\else\fi
  \else\expandafter\math@\meaning@\math@
  \ifgtest@\expandafter\mathbin@\meaning@\mathbin@
  \ifgtest@\gdef\thedots@{\dotsb@}%
  \else\expandafter\mathrel@\meaning@\mathrel@
  \ifgtest@\gdef\thedots@{\dotsb@}%
  \fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi
 \thedots@}
%    \end{macrocode}
%
%    The \verb|=| character is necessary in the two \verb|\let| assignments
%    in \verb|\boldsymboldots@|, because the symbol we are making
%    bold might be an \verb|=| sign.
%    \begin{macrocode}
\def\boldsymboldots@#1{\bold@true\let\@let@token=#1\let\delayed@=#1\mdots@@
 \boldsymbol#1\bold@false}
%    \end{macrocode}
%
%    The definition of |\@cdots| is merely the \fn{plain.tex}
%    definition of |\cdots|.
%    \begin{macrocode}
\def\@cdots{\mathinner{\cdotp\cdotp\cdotp}}
\def\dotsi{\!\@cdots}
\let\dotsb@\@cdots
%    \end{macrocode}
%
%    If any new right delimiters are defined, they would need to be
%    added to the definition of \verb|\rightdelim@| in order for \verb|\dots|
%    to work properly in all cases.
%    \begin{macrocode}
\def\rightdelim@{\gtest@true
 \ifx\@let@token)\else
 \ifx\@let@token]\else
 \ifx\@let@token\rbrack\else
 \ifx\@let@token\}\else
 \ifx\@let@token\rbrace\else
 \ifx\@let@token\rangle\else
 \ifx\@let@token\rceil\else
 \ifx\@let@token\rfloor\else
 \ifx\@let@token\rgroup\else
 \ifx\@let@token\rmoustache\else
 \ifx\@let@token\right\else
 \ifx\@let@token\bigr\else
 \ifx\@let@token\biggr\else
 \ifx\@let@token\Bigr\else
 \ifx\@let@token\Biggr\else\gtest@false
 \fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi\fi}
\def\extra@{%
 \rightdelim@\ifgtest@
 \else\ifx\@let@token$\gtest@true
 \else\xdef\meaning@{\meaning\@let@token..........}%
 \expandafter\macro@\meaning@\macro@\ifgtest@
 \expandafter\DOTS@\meaning@\DOTS@
 \ifgtest@
 \ifnum\DOTSCASE@=\tw@\gtest@true\else\gtest@false
 \fi\fi\fi\fi\fi}
\newif\ifbold@
\def\dotso@{\relaxnext@
 \ifbold@
  \let\@let@token\delayed@
  \def\nextii@{\extra@\@ldots\ifgtest@\,\fi}%
 \else
  \def\nextii@{\DN@{\extra@\@ldots\ifgtest@\,\fi}\FN@\next@}%
 \fi
 \nextii@}
%    \end{macrocode}
%    Why not save some tokens? (space vs. time).
%    \begin{macrocode}
\def\extrap@#1{%
 \DN@{#1\,}%
 \ifx\@let@token,\else
 \ifx\@let@token;\else
 \ifx\@let@token.\else\extra@
 \ifgtest@\else
 \let\next@#1\fi\fi\fi\fi\next@}
%    \end{macrocode}
%
%    \begin{macrocode}
\DeclareRobustCommand{\ldots}{\DN@{\extrap@\@ldots}\FN@\next@}
\DeclareRobustCommand{\cdots}{\DN@{\extrap@\@cdots}\FN@\next@}
\let\dotso\ldots
\let\dotsb\cdots
\let\dotsm\dotsb
\DeclareRobustCommand{\dotsc}{%
  \DN@{\ifx\@let@token;\@ldots\,%
       \else \ifx\@let@token.\@ldots\,%
       \else \extra@\@ldots \ifgtest@\,\fi
       \fi\fi}%
  \FN@\next@}
\def\longrightarrow{\DOTSB\relbar\joinrel\rightarrow}
\def\Longrightarrow{\DOTSB\Relbar\joinrel\Rightarrow}
\def\longleftarrow{\DOTSB\leftarrow\joinrel\relbar}
\def\Longleftarrow{\DOTSB\Leftarrow\joinrel\Relbar}
\def\longleftrightarrow{\DOTSB\leftarrow\joinrel\rightarrow}
\def\Longleftrightarrow{\DOTSB\Leftarrow\joinrel\Rightarrow}
\def\mapsto{\DOTSB\mapstochar\rightarrow}
\def\longmapsto{\DOTSB\mapstochar\longrightarrow}
\def\hookrightarrow{\DOTSB\lhook\joinrel\rightarrow}
\def\hookleftarrow{\DOTSB\leftarrow\joinrel\rhook}
\def\doteq{\DOTSB\buildrel\textstyle.\over=}
\def\iff{\DOTSB\;\Longleftrightarrow\;}
%    \end{macrocode}
%
%    Remove the `variable' code 7 at the beginning of cap Greek
%    mathchardefs. These letters should only be made bold via
%    |\boldsymbol|, for consistency with lowercase Greek. If cap Gamma
%    does not have the expected definition (\mathchar"7000), skip this
%    section.
%    \begin{macrocode}
\mathchardef\@tempa=\string"7000
\ifx\@tempa\Gamma
  \DeclareMathSymbol{\Gamma}{\mathord}{operators}{"00}
  \DeclareMathSymbol{\Delta}{\mathord}{operators}{"01}
  \DeclareMathSymbol{\Theta}{\mathord}{operators}{"02}
  \DeclareMathSymbol{\Lambda}{\mathord}{operators}{"03}
  \DeclareMathSymbol{\Xi}{\mathord}{operators}{"04}
  \DeclareMathSymbol{\Pi}{\mathord}{operators}{"05}
  \DeclareMathSymbol{\Sigma}{\mathord}{operators}{"06}
  \DeclareMathSymbol{\Upsilon}{\mathord}{operators}{"07}
  \DeclareMathSymbol{\Phi}{\mathord}{operators}{"08}
  \DeclareMathSymbol{\Psi}{\mathord}{operators}{"09}
  \DeclareMathSymbol{\Omega}{\mathord}{operators}{"0A}
  \DeclareMathSymbol{\varGamma}{\mathord}{letters}{"00}
  \DeclareMathSymbol{\varDelta}{\mathord}{letters}{"01}
  \DeclareMathSymbol{\varTheta}{\mathord}{letters}{"02}
  \DeclareMathSymbol{\varLambda}{\mathord}{letters}{"03}
  \DeclareMathSymbol{\varXi}{\mathord}{letters}{"04}
  \DeclareMathSymbol{\varPi}{\mathord}{letters}{"05}
  \DeclareMathSymbol{\varSigma}{\mathord}{letters}{"06}
  \DeclareMathSymbol{\varUpsilon}{\mathord}{letters}{"07}
  \DeclareMathSymbol{\varPhi}{\mathord}{letters}{"08}
  \DeclareMathSymbol{\varPsi}{\mathord}{letters}{"09}
  \DeclareMathSymbol{\varOmega}{\mathord}{letters}{"0A}
\fi
%    \end{macrocode}
%
%    We want to change the leading digit of math accents to be
%    |\accentclass@" so that it can vary according to certain internal
%    purposes.
%    \begin{macrocode}
\def\accentclass@{7}
\def\noaccents@{\def\accentclass@{0}}
%    \end{macrocode}
%
%    There are a few \meta{math alphabet}s in the standard fonts where we
%    have to change the extra macros because the standard definitions
%    don't account for these accent problems. The first is for the
%    |\mathit| command.
%    \begin{macrocode}
\DeclareFontEncoding{OML}{}{\noaccents@}
%    \end{macrocode}
%    The next one corrects the |\cal| alphabet.
%    \begin{macrocode}
\DeclareFontEncoding{OMS}{}{\noaccents@}
%    \end{macrocode}
%
%    Now let's change the accent commands.
%    \begin{macrocode}
\edef\@tempa#1#2{\def#1{\mathaccent\string"\noexpand\accentclass@#2 }}
\@tempa\hat{05E}
\@tempa\check{014}
\@tempa\tilde{07E}
\@tempa\acute{013}
\@tempa\grave{012}
\@tempa\dot{05F}
\@tempa\ddot{07F}
\@tempa\breve{015}
\@tempa\bar{016}
\newcount\skewcharcount@
\newcount\familycount@
\def\theskewchar@{\familycount@\@ne
 \global\skewcharcount@\the\skewchar\textfont\@ne
 \ifnum\mathgroup>\m@ne\ifnum\mathgroup<16
  \global\familycount@\the\mathgroup\relax
  \global\skewcharcount@\the\skewchar\textfont\the\mathgroup\relax\fi\fi
 \ifnum\skewcharcount@>\m@ne
  \ifnum\skewcharcount@<128
  \multiply\familycount@256
  \global\advance\skewcharcount@\familycount@
  \global\advance\skewcharcount@28672
  \mathchar\skewcharcount@\else
  \global\skewcharcount@\m@ne\fi\else
 \global\skewcharcount@\m@ne\fi}
\newcount\pointcount@
\def\getpoints@#1.#2\getpoints@{\pointcount@#1 }
\newdimen\accentdimen@
\newcount\accentmu@
\def\dimentomu@{\multiply\accentdimen@ 100
 \expandafter\getpoints@\the\accentdimen@\getpoints@
 \multiply\pointcount@18
 \divide\pointcount@\@m
 \global\accentmu@\pointcount@}

\def\mathaccent@#1#2{\ifnum\mathgroup=\m@ne\xdef\thefam@{1}\else
 \xdef\thefam@{\the\mathgroup}\fi
 \accentdimen@\z@
 \setboxz@h{\unbracefonts@$\m@th\mathgroup\thefam@\relax#2$}%
 \ifdim\accentdimen@=\z@\DN@{\mathaccent#1{#2}}%
  \setbox\@ne\hbox{\unbracefonts@
    $\m@th\mathgroup\thefam@\relax#2\theskewchar@$}
  \setbox\tw@\hbox{$\m@th\ifnum\skewcharcount@=\m@ne\else
   \mathchar\skewcharcount@\fi$}%
  \global\accentdimen@\wd\@ne\global\advance\accentdimen@-\wdz@
  \global\advance\accentdimen@-\wd\tw@
  \global\multiply\accentdimen@\tw@
  \dimentomu@\global\advance\accentmu@\@ne
 \else\DN@{{\mathaccent#1{#2\mkern\accentmu@ mu}%
    \mkern-\accentmu@ mu}{}}\fi
 \next@}
%    \end{macrocode}
%
% \begin{macro}{\unbracefonts@}
%    The |\unbracefonts@| macro is used to
%    get rid of the braces of a \meta{math alphabet identifier}.
%    \begin{macrocode}
\def\unbracefonts@{\let\math@bgroup\@empty\let\math@egroup\@empty}
%    \end{macrocode}
% \end{macro}
%
%    The commands |\Hat|, |\Tilde|, \ldots, are not made robust
%    because they are clearly complex commands, not used that often,
%    and we dont want to use up the extra string pool/csnames that
%    robustness would require.
%    \begin{macrocode}
\begingroup \catcode`\"=12
\def\@tempa#1#2{\gdef#1{\RIfM@\DN@{\mathaccent@{"\accentclass@#2 }}%
  \else\DN@{\nonmatherr@{#1}}\fi\next@}}
\@tempa\Hat{05E}
\@tempa\Check{014}
\@tempa\Tilde{07E}
\@tempa\Acute{013}
\@tempa\Grave{012}
\@tempa\Dot{05F}
\@tempa\Ddot{07F}
\@tempa\Breve{015}
\@tempa\Bar{016}
\gdef\Vec{\RIfM@\DN@{\mathaccent@{"017E }}\else
 \DN@{\nonmatherr@\Vec}\fi\next@}
\endgroup
%    \end{macrocode}
%
%     The reason for redefining \verb+\@@sqrt+ (used by \LaTeX{}'s
%     definition of \verb+\sqrt+) to read an argument is discussed in
%     Spivak's amstex.doc.  As an example, if \verb+\xD+ is defined as
%     \verb+\not D+ then \verb+\sqrt\xD+ produces this:
%     $\catcode`\"=12 \def\xD{\not D}\radical"270370 \xD$, with the
%     slash separated from the $D$.  (The same thing happens with
%     \verb+^\xD+, by the way, but that is not so easy to fix.) This
%     refinement doesn't gain much if the user is careful and always
%     puts braces around the argument of \verb+\sqrt+, but it costs
%     little. MJD
%
%    \begin{macrocode}
\begingroup \catcode`\"=12
\gdef\@@sqrt#1{\radical"270370 {#1}}
\endgroup
%    \end{macrocode}
%
%     \verb+\overline@+ replaced by \verb+\@@overline+, to be
%     consistent with the \LaTeX{} name \verb+\@@underline+.
%     \verb+\overline+ is redefined for the same reason as
%     with \verb+\@@sqrt+.
%    \begin{macrocode}
\@saveprimitive\overline\@@overline
\def\overline#1{\@@overline{#1}}
%    \end{macrocode}
%
%    The |\boxed| command is specifically intended to put a box around
%    an equation or piece of an equation. (Not incl. the equation
%    number.) This isn't trivial for end-users to do it properly
%    with |\fbox| so we provide a command for them.
%    \begin{macrocode}
\def\boxed#1{\fbox{\m@th$\displaystyle#1$}}
%    \end{macrocode}
%
% \subsection{Preliminary macros}
%
% \begin{macro}{\setb@ck}
%    The macro \verb+\setb@ck+ decrements the {\tt equation} counter
%    by one.  To avoid doing this twice in constructs that are
%    evaluated several times the \verb+firstchoice@+ switch is
%    checked.
%    \begin{macrocode}
\def\setb@ck{\iffirstchoice@\global\advance\c@equation\m@ne\fi}
%    \end{macrocode}
% \end{macro}
%
% The following macros implement the \LaTeX{} syntax for the \verb+\\+
% command, i.e. the possibility to add an asterisk to inhibit a page
% break, or an optional argument to denote additional vertical space.
% They are modelled more or less after the corresponding macros for
% \LaTeX's \verb+eqnarray+ and \verb+array+ environments.
%
% (Internal remark:
% we can use the eqnarray mechanism if we change it so that it also uses
% the AMS-TeX \verb+\openup+ but this can be done later)
%
% \begin{macro}{\dspbrk@lvl}
%    We begin by defining the \verb+\dspbrk@lvl+ counter. This counter
%    records the desirability of a break after the current row, as a
%    number between $0$ and $4$. Its default value is $-1$ meaning that
%    no explicit \verb+\displaybreak+ command was given, and the default
%    \verb+\interdisplaylinepenalty+ is to be used.
%    \begin{macrocode}
\newcount\dspbrk@lvl
\dspbrk@lvl=-1
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\interdisplaylinepenalty}
%    We set the \verb+\interdisplaylinepenalty+ to $10000$.
%    \begin{macrocode}
\interdisplaylinepenalty\@M
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\allowdisplaybreaks}
%    The \verb+\allowdisplaybreaks+ declaration.
%    \begin{macrocode}
\def\allowdisplaybreaks{%
  \new@ifnextchar[\allowdspbrks@{\allowdspbrks@[4]}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\allowdspbrks@}
%    Here we simply fetch a suitable value for
%    \verb+\interdisplaylinepenalty+.
%    \begin{macrocode}
\def\allowdspbrks@[#1]{%
  \interdisplaylinepenalty\getdsp@pen{#1}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\getdsp@pen}
%    Modelled after \LaTeX's \verb+\@getpen+.  We use higher numbers
%    than would normally be provided by \verb+\@lowpenalty+,
%    \verb+\@medpenalty+, and \verb+\@highpenalty+, since display
%    breaks are almost always less desirable.
%    \begin{macrocode}
\def\getdsp@pen#1{%
  \ifcase #1\relax \@M
    \or 9999
    \or 6999
    \or 2999
    \or \z@\fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\displaybreak}
% \begin{macro}{\displaybreak@}
% \begin{macro}{\dspbrk@}
%    For breaks in a certain row of a alignment.
%    \begin{macrocode}
\def\displaybreak{\PackageError{amstex}{\Invalid@@\displaybreak}\@eha}

\def\displaybreak@{%
  \def\displaybreak{\new@ifnextchar[\dspbrk@{\dspbrk@[4]}}}

\def\dspbrk@[#1]{\global\dspbrk@lvl #1\relax}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\math@cr}
%    The macro \verb+\math@cr+ ends a row inside one of the \AmSTeX{}
%    environments, i.e. this is the internal name of the \verb+\\+
%    commands in these environments. As usual for this kind of macro
%    inside of alignments we insert a special brace into \TeX's input
%    stream.
%    \begin{macrocode}
\def\math@cr{{\ifnum0=`}\fi
%    \end{macrocode}
%    The first step is now to check whether an asterisk follows.
%    \verb+\@eqpen+ is used to hold the penalty value to be put on
%    the vertical list.
%    Then we call up \verb+\math@cr@+ which performs the next step.
%    If an asterisk is read page breaking is inhibited.
%    \begin{macrocode}
  \new@ifstar{\global\@eqpen\@M\math@cr@}%
%    \end{macrocode}
%    Otherwise we have to check the \verb+\dspbrk@lvl+ value.
%    \begin{macrocode}
          {\global\@eqpen
             \ifnum\dspbrk@lvl <\z@ \interdisplaylinepenalty
              \else -\@getpen\dspbrk@lvl \fi
           \math@cr@}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\math@cr@}
%    The purpose of \verb+\math@cr@+ is to check whether an optional
%    argument follows.  If not it provides \verb+\z@+ as default
%    value.
%    \begin{macrocode}
\def\math@cr@{\new@ifnextchar[\math@cr@@{\math@cr@@[\z@]}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\math@cr@@}
%    \verb+\math@cr@@+ closes the special brace opened in
%    \verb+\math@cr+, and calls \verb+\math@cr@@@+ which is supposed
%    the `real' row ending command.  The meaning of this macro depends
%    on the environment in which it is used.
%    \begin{macrocode}
\def\math@cr@@[#1]{\ifnum0=`{\fi}\math@cr@@@
%    \end{macrocode}
%    Finally we put the additional space onto the vertical list.
%    \begin{macrocode}
  \noalign{\vskip#1\relax}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\Let@}
%    \verb+\Let@+ is called by all environments where \verb+\\+
%    ends a row of an alignment.
%    \begin{macrocode}
\def\Let@{\let\\\math@cr}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\restore@math@cr}
%    We mentioned already that the exact meaning of \verb+\math@cr@@@+
%    depends on the current environment.  Since it is often a simple
%    \verb+\cr+ we provide \verb+\restore@math@cr+ to reset it.
%    \begin{macrocode}
\def\restore@math@cr{\def\math@cr@@@{\cr}}
%    \end{macrocode}
%    This is also the default case.
%    \begin{macrocode}
\restore@math@cr
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\intertext}
% \begin{macro}{\intertext@}
%    The intertext command is used for inserting text between the
%    rows of an alignment.  It's use is only allowed in special
%    places.
%
%    Intertext might better be done as an environment, but the
%    |\begingroup| from |\begin| would cause the |\noalign| to fail.
%    \begin{macrocode}
\def\intertext{\PackageError{amstex}{\Invalid@@\intertext}\@eha}
%    \end{macrocode}
%    \verb+\intertext@+ is called by all environments that allow
%    the use of the \verb+\intertext+ command.
%    \begin{macrocode}
\def\intertext@{\def\intertext##1{\noalign{%
  \penalty\postdisplaypenalty\vskip\belowdisplayskip
  \vbox{\normalbaselines\noindent##1}%
  \penalty\predisplaypenalty\vskip\abovedisplayskip}}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%
% \subsection{Implementing tags}
%
%    In this section we describe some of the macros needed to make the
%    \verb+\tag+ command work in various places. We start by defining a
%    help text to be used when a \verb+\tag+ command is used somewhere
%    it should not appear.
%
% \begin{macro}{\tag@help}
%    This is the default error help text provided when \verb+\tag+
%    generates an error message.
%    Note that \verb+\newhelp+ generates a control sequence name
%    from the string given as its argument so that a leading
%    backslash is provided automatically.
%    \begin{macrocode}
\newhelp\tag@help
  {tag cannot be used at this point.\space
   If you don't understand why^^Jyou should consult
   the documentation.^^JBut don't worry: just continue, and I'll
   forget what happened.}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\gobble@tag}
%    This macro is to be used when \verb+\tag+ should silently
%    skip its argument.
%    It is made to handle the \verb+*+-form of \verb+\tag+ as well.
%    \begin{macrocode}
\def\gobble@tag{\new@ifstar\@gobble\@gobble}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\invalid@tag}
%    \verb+\invalid@tag+ is a macro that should be used whenever
%    \verb+\tag+ appears in an illegal place.
%    It sets up \verb+\tag@help+ (as defined above) as help message,
%    prints its argument as error message, and skips \verb+\tag+'s
%    argument.
%    \begin{macrocode}
\def\invalid@tag#1{\PackageError{amstex}{#1}{\the\tag@help}\gobble@tag}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\dft@tag}
% \begin{macro}{\default@tag}
%    \verb+\dft@tag+ provides a convenient way to disallow the
%    use of \verb+\tag+ at certain points.
%    One simply has to write
%    \begin{verbatim}
%\let\tag\dft@tag
%    \end{verbatim}
%    and the \verb+\tag+ command will produce an error message,
%    with a suitable error help text, and discard its argument.
%    \begin{macrocode}
\def\dft@tag{\invalid@tag{\string\tag\space not allowed here}}
%    \end{macrocode}
%    Since this is used several times we provide an abbreviation for
%    it.
%    \begin{macrocode}
\def\default@tag{\let\tag\dft@tag}
%    \end{macrocode}
%    Since this is also the default, i.e.\ the \verb+\tag+ command
%    should not be used except in special places, we issue a
%    \verb+\default@tag+ command.
%    \begin{macrocode}
\default@tag
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%
%    Now that we have taken care of the case that \verb+\tag+ is not
%    allowed we will provide some macros to process tags appropriately.
%    As the user documentation states, a \verb+\tag+ command (without
%    the asterisk typesets its argument according to the document
%    styles' conventions, whereas a \verb+\tag*+ command typesets its
%    argument exactly as given. We define therefore the following
%    interface:
%
% \begin{macro}{\maketag@@}
% \begin{macro}{\maketag@@@}
% \begin{macro}{\tagform@}
%    \verb+\tag+ is supposed to call \verb+\maketag@@+ which checks
%    whether an asterisk follows. If this is the case it calls up
%    \verb+\maketag@@@+ which sets its argument `as is'. Otherwise
%    \verb+\tagform@+ is called to do the job. (This macro is to be
%    defined appropriately by the document style.)
%    \begin{macrocode}
\def\maketag@@{\new@ifstar\maketag@@@\tagform@}
%    \end{macrocode}
%     We define \verb+\maketag@@@+ to use the normal font of the
%    document text (since this is the usual practice for numbering of
%    document elements) and to put a box around the tag. Furthermore we
%    use \verb+\m@th+ for exceptional cases where the tag involves a
%    superscript or some such math. (Probably from an explicit use of
%    \verb+\tag*+ rather than from the automatic numbering.)
%    \begin{macrocode}
\def\maketag@@@#1{\hbox{\m@th\normalfont#1}}
%    \end{macrocode}
%    We use the following default definition for \verb+\tagform@+
%    that puts only parentheses around the tag.
%    \begin{macrocode}
\def\tagform@#1{\maketag@@@{(\ignorespaces#1\unskip)}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\thetag}
%    Sometimes one needs to set a literal tag according to the rules of
%    the document style. To achieve this we provide the \verb+\thetag+
%    command. It typesets its argument by calling \verb+\tagform@+ on
%    it.
%    \begin{macrocode}
\def\thetag{\leavevmode\tagform@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\df@tag}
% \begin{macro}{\make@df@tag}
% \begin{macro}{\make@df@tag@@}
% \begin{macro}{\make@df@tag@@@}
%    Sometimes it is necessary for a \verb+\tag+ command to store a tag
%    in a safe place and to process it later, e.g., for a tag in a row
%    of an alignment where the tag can only be typeset when the
%    \verb+\\+ at the end of the row was seen. Such a tag is stored in
%    the macro \verb+\df@tag+ (for `deferred tag'). For this purpose we
%    provide the \verb+\make@df@tag+ macro. It is built very similar to
%    the \verb+\maketag@@+ macro above.
%    \begin{macrocode}
\def\make@df@tag{\new@ifstar\make@df@tag@@\make@df@tag@@@}
%    \end{macrocode}
%    \verb+\make@df@tag+ sets \verb+\@currentlabel+ and defines
%    \verb+\df@tag+ appropriately.
%    \begin{macrocode}
\def\make@df@tag@@#1{%
  \def\@currentlabel{#1}%
  \gdef\df@tag{\maketag@@@{#1}}}
%    \end{macrocode}
%    \verb+\make@df@tag@@@+ does the same if the tag is to be typeset
%    according to the document style's conventions.
%    \begin{macrocode}
\def\make@df@tag@@@#1{\@seteqlabel{#1}\gdef\df@tag{\tagform@{#1}}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
%  \begin{macro}{\@seteqlabel}
%    Abbreviation for a common construction to set the current label to
%    the current equation number.
%    \begin{macrocode}
\def\@seteqlabel#1{\toks@\@xp{\p@equation{#1}}%
  \edef\@currentlabel{\the\toks@}}
%    \end{macrocode}
%  \end{macro}
%
%     For consistency we provide \verb+\notag+, equivalent to
%     \verb+\nonumber+.  The alternative would have been to rename
%     \verb+\tag+ as \verb+\number+ to go along with \verb+\nonumber+,
%     but of course \verb+\number+ is a \TeX{} primitive that should not
%     be redefined.
% \begin{macro}
\def\notag{\nonumber}
% \end{macro}
%
%    Depending on the setting of the iftagsleft switch, we may need to
%    redefine \cs{@eqnnum}.
%    \begin{macrocode}
\iftagsleft@
\def\@eqnnum{\hbox to1sp{}\rlap{\normalfont
    \hskip -\displaywidth\tagform@\theequation}}
\fi
%    \end{macrocode}
% \end{macro}

%    DMJ: TAG ADJUSTMENT
%    \begin{macro}{\adjusttag}
%    \begin{macro}{\@adjusttag}
%    \begin{macro}{\@movetag}
%    DMJ: Usage: \cn{adjusttag} \meta{dimen}
%
%    DMJ: This will shift the next tag by \meta{dimen} in the vertical
%    direction in \emph{only} the next \cn{equation}, \cn{gather},
%    \cn{align}, or \cn{multline} environment.
%    (mjd: \cs{@adjusttag} is a
%    macro rather than a dimen register because those tend to get used up
%    by add-on packages and there's no way around the upper limit of 256.)
%    \begin{macrocode}
\let\@adjusttag\@empty

\def\adjusttag#1{\skip@#1\relax\gdef\@adjusttag{#1}}

\def\@movetag{%
    \ifx\@adjusttag\@empty \else
        \vskip\@adjusttag\relax
        \global\let\@adjusttag\@empty
    \fi
}
%    \end{macrocode}
%    \end{macro}
%    \end{macro}
%    \end{macro}
%
% \subsection{The {\tt Sb} and {\tt Sp} environments}
%
% The {\tt Sb} and {\tt Sp} environments are used to set subscripts
% and superscripts that consists of several lines.
% The main task of this is done by the macro \verb+\multilimits@+.
% \begin{macro}{\multilimits@}
%    This macro sets up a horizontal alignment to set the lines.
%    The first few parts of this macro are worth considering in
%    detail since they are used in a very similar way in all
%    math alignment macros.
%
%    The macro starts by opening a group to enclose the whole
%    subscript or superscript.
%    \begin{macrocode}
\def\multilimits@{\bgroup
%    \end{macrocode}
%    Then we use \verb+\Let@+ to set the proper meaning of the
%    \verb+\\+ and \verb+\\*+ commands.
%    \begin{macrocode}
  \Let@
%    \end{macrocode}
%    Now we restore the meaning of \verb+\math@cr@@@+ to \verb+\cr+
%    (see above) as this may be used in one of the more complicated
%    alignment macros where the meaning of \verb+\math@cr@@@+ is
%    different.
%    \begin{macrocode}
  \restore@math@cr
%    \end{macrocode}
%    Then we call \verb+\default@tag+ since tags are not allowed
%    inside a {\tt Sb} or {\tt Sp} environment.
%    \begin{macrocode}
  \default@tag
%    \end{macrocode}
%    The rest of the \verb+\multilimits+ macro is rather
%    straightforward code to get the correct line spacing\ldots
%    \begin{macrocode}
 \baselineskip\fontdimen10 \scriptfont\tw@
 \advance\baselineskip\fontdimen12 \scriptfont\tw@
 \lineskip\thr@@\fontdimen8 \scriptfont\thr@@
 \lineskiplimit\lineskip
%    \end{macrocode}
%    \ldots followed by a box containing the actual alignment.
%    \begin{macrocode}
 \vbox\bgroup\ialign\bgroup\hfil$\m@th\scriptstyle{##}$\hfil\crcr}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\Sb}
% \begin{macro}{\Sp}
% \begin{macro}{\endSb}
% \begin{macro}{\endSp}
%    The definitions of \verb+\Sb+ and \verb+\Sp+ are then easy:
%    \begin{macrocode}
\def\Sb{_\multilimits@}
\def\Sp{^\multilimits@}
%    \end{macrocode}
%    The environments end with a number of group closing braces.
%    \begin{macrocode}
\def\endSb{\crcr\egroup\egroup\egroup}
\let\endSp=\endSb
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
%
% \subsection{Matrices}
%
% \begin{macro}{\smallmatrix}
% \begin{macro}{\endsmallmatrix}
%     \verb+\smallmatrix+ is again an alignment, this time in a
%     centered box. The opening incantations are basically the same as
%     those in \verb+\multilimits@+, followed by the alignment itself.
%     A remark: the baselineskip (\verb+9\ex@+) used in \AmSTeX{} is
%     too large for use in text with the usual baselineskip of $12$ or
%     $13$ points; we change it here to \verb+6\ex@+ and also adjust
%     the \verb+\lineskip+ and \verb+\lineskiplimit+ slightly to
%     compensate. (MJD)
%    \begin{macrocode}
\def\smallmatrix{\null\,\vcenter\bgroup
 \Let@\restore@math@cr\default@tag
 \baselineskip6\ex@ \lineskip1.5\ex@ \lineskiplimit\lineskip
 \ialign\bgroup\hfil$\m@th\scriptstyle{##}$\hfil&&\thickspace\hfil
 $\m@th\scriptstyle{##}$\hfil\crcr}
%    \end{macrocode}
%    The corresponding \verb+\endsmallmatrix+ macro has only to
%    finish the alignment and to close the groups.
%    \begin{macrocode}
\def\endsmallmatrix{\crcr\egroup\egroup\,}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\matrix}
% \begin{macro}{\endmatrix}
% \begin{macro}{\c@MaxMatrixCols}
%    For the matrix environment we provide only a very simple
%    macro: an {\tt array} environment with a predefined number of
%    centered columns.
%    This number is defined by the counter {\tt MaxMatrixCols} whose
%    default value is $10$.
%    \begin{macrocode}
\newcount\c@MaxMatrixCols
\c@MaxMatrixCols=10

\def\matrix{\hskip -\arraycolsep\array{*\c@MaxMatrixCols c}}
\def\endmatrix{\endarray \hskip -\arraycolsep}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\@array}
%    \LaTeX's \verb+\@array+ macro has a bug: it uses \verb+\halign+
%    instead of \verb+\ialign+ which initializes the \verb+\tabskip+
%    glue to zero. We define a corrected version here.
%
%    But this should only be done when the original \LaTeX{} {\tt
%    array} environment is used, not when Frank's version was loaded.
%    This is tested by checking the macro \verb+\prepnext@tok+.
%    \begin{macrocode}
\@ifundefined{prepnext@tok}{%
  \def\@array[#1]#2{%
    \setbox\@arstrutbox\hbox{\vrule\@height\arraystretch\ht\strutbox
       \@depth\arraystretch\dp\strutbox \@width\z@}%
    \@mkpream{#2}\edef\@preamble{\ialign \noexpand\@halignto
    \bgroup \tabskip\z@ \@arstrut \@preamble \tabskip\z@ \cr}%
    \let\@startpbox\@@startpbox \let\@endpbox\@@endpbox
    \if #1t\vtop \else \if#1b\vbox \else \vcenter \fi\fi
%    \end{macrocode}
%    \verb+\par+ set to \verb+\@empty+ to allow blank lines
%    in array entries.
%    \begin{macrocode}
    \bgroup \let\par\@empty
    \let\@sharp##\let\protect\relax
    \lineskip\z@\baselineskip\z@\@preamble}%
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@xexpast}
%    We also need to substitute nonactive \verb|@| characters for
%    active ones in a preamble specification for \verb|{array}| or
%    \verb|{tabular}| or \verb|{multicolumn}|. We do this by defining
%    active \verb|@| to be (letter) \verb|@| temporarily, while some
%    \verb|\edef|'s are taking place. All \verb|@| characters
%    anywhere in the preamble will be expanded, so
%    \verb|@| characters that are not the beginning of
%    a column-specifier \verb|@|-expression will be improperly
%    expanded and cause an error message; however, this possibility
%    is unlikely enough that we will just ignore it. (And I suppose
%    that a \verb|\protect| before the \verb|@| might actually work.)
%
%    While defining \verb|\@xexpast|, we use a standard \verb|\lccode|
%    trick to obtain an active \verb|@| character in the midst of
%    normal \LaTeX{} code with nonactive \verb|@| characters.
%
%    One more stratagem that we use here is enclosing the main action
%    of \verb|\@xexpast| in a group so that we don't have to worry
%    about restoring the proper definition of active \verb|@|
%    afterwards; this entails the use of a special trick to throw the
%    definition of \verb|\@tempa| beyond the \verb|\endgroup|, to
%    avoid defining it globally.
%    \begin{macrocode}
\begingroup \lccode`\~=`\@ \catcode`\~=\active % just to be sure!
\lowercase{%
\gdef\@xexpast#1*#2#3#4\@@{\begingroup
  \def~{@}\edef\reserved@a{#1}\@tempcnta#2\relax
  \ifnum\@tempcnta >\z@
    \@whilenum\@tempcnta >\z@\do
      {\edef\reserved@a{\reserved@a#3}\advance\@tempcnta \m@ne}%
    \let\reserved@b\@xexpast
  \else \let\reserved@b\@xexnoop\fi
  \expandafter\reserved@b \reserved@a #4\@@
%    \end{macrocode}
%    We want to expand the second \verb|\reserved@a| before we leave the
%    current group:
%    \begin{macrocode}
  \expandafter\endgroup
  \expandafter\def\expandafter\reserved@a\expandafter{\reserved@a}%
%    \end{macrocode}
%    For compatibility with the June 1994 version of \latex/ we need to
%    supply both \cs{reserved@a} and \cs{@tempa} to the parent function
%    \cs{@mkpream}.
%    \begin{macrocode}
  \let\@tempa\reserved@a
}% End of \@xexpast
}% End of \lowercase
%    \end{macrocode}
%    End the group where \verb|~| has lccode equal to \verb|@|.
%    \begin{macrocode}
\endgroup
%    \end{macrocode}
% \end{macro}
%
%    \begin{macrocode}
}{}% End of \@ifundefined test.
%    \end{macrocode}
%
%     |\matrix| is defined in terms of |\array|.
%    \begin{macrocode}
\def\pmatrix{\left(\matrix}
\def\endpmatrix{\endmatrix\right)}
\def\bmatrix{\left[\matrix}
\def\endbmatrix{\endmatrix\right]}
\def\vmatrix{\left|\matrix}
\def\endvmatrix{\endmatrix\right|}
\def\Vmatrix{\left\|\matrix}
\def\endVmatrix{\endmatrix\right\|}
%    \end{macrocode}
%
%    \begin{macrocode}
\let\hdots\@ldots
%    \end{macrocode}
%
%    \begin{macrocode}
\def\hdotsfor#1{\if\noexpand#1[\expandafter\shdots@for\else
                \hdots@for\@ne{#1}\fi}
\newmuskip\dotsspace@
\def\shdots@for#1]{\hdots@for{#1}}
\def\hdots@for#1#2{\multicolumn{#2}c%
  {\m@th\dotsspace@1.5mu\mkern-#1\dotsspace@
   \xleaders\hbox{$\m@th\mkern#1\dotsspace@.\mkern#1\dotsspace@$}%
           \hfill
   \mkern-#1\dotsspace@}%
   }
%    \end{macrocode}
%
% \begin{macro}{\cases}
% \begin{macro}{\endcases}
%    The \verb+cases+ environment is easily implemented in terms
%    of \LaTeX's {\tt array} environment.
%    \begin{macrocode}
\def\cases{\left\{\def\arraystretch{1.2}\hskip-\arraycolsep
  \array{l@{\quad}l}}
\def\endcases{\endarray\hskip-\arraycolsep\right.}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%
% \subsection{Math alignment environments}
%
% \subsubsection{Preliminaries}
%
% \begin{macro}{\ifinany@}
% \begin{macro}{\ifinalign@}
% \begin{macro}{\ifingather@}
%    We define three switches that are set to true in certain
%    alignments: \verb+inalign@+ and \verb+ingather@+ inside of
%    the {\tt align} and {\tt gather} environments, respectively,
%    and \verb+inany@+ that is set true in any of these
%    environments.
%    These switches are needed to control certain actions that
%    depend on the surrounding conditions, more specifically:
%    on the setting already done by the surrounding environments.
%    \begin{macrocode}
\newif\ifinany@
\newif\ifinalign@
\newif\ifingather@
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\and@}
%    The counter \verb+\and@+ is used by the alignment macros to
%    keep track of the current column.
%    \begin{macrocode}
\newcount\and@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\iftag@}
%    The switch \verb+tag@+ is set to false at the beginning of every
%    row and set to true by a \verb+\tag+ command.
%    This allows us to check whether there is more than one tag on
%    a row.
%    \begin{macrocode}
\newif\iftag@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\andhelp@}
%    The help text stored in \verb+\andhelp@+ is used for errors
%    generated by too many \verb+&+ characters in a row.
%    \begin{macrocode}
\newhelp\andhelp@
{An extra & here is so disastrous that you should probably exit^^J
and fix things up.}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ifst@rred}
%    The switch \verb+st@rred+ is set to true by all starred
%    environments
%    and set to false by the unstarred versions.
%    \begin{macrocode}
\newif\ifst@rred
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{Scanning the environments' body}
%
% Several of the math alignment macros must scan their body twice:
% once to determine how wide the columns are and then to actually
% typeset them.
% This means that we must collect all text in this body before
% calling the environment macros.
%
% \begin{macro}{\@envbody}
%    We start by defining a token register to contain the body.
%    \begin{macrocode}
\newtoks\@envbody
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\addto@envbody}
%    Then we define a macro to add something (i.e.\ its argument)
%    to the token register \verb+\@envbody+.
%    \begin{macrocode}
\def\addto@envbody#1{\@envbody\expandafter{\the\@envbody#1}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\collect@body}
%    The macro \verb+\collect@body+ starts the scan for the
%    \verb+\end{+\ldots\verb+}+ command of the current environment.
%    It takes a macro name as argument.  This macro is supposed
%    to take the whole body of the environment as its argument.
%    For example, \verb+\begin{align}+ would call
%    \verb+\collect@body\@align+ if \verb+\@align#1{+\ldots\verb+}+
%    is the macro that sets the alignment with body \verb+#1+.
%
%    \verb+\collect@body+ first initializes the token register
%    \verb+\@envbody+.
%    \begin{macrocode}
\def\collect@body#1{%
  \@envbody{}%
%    \end{macrocode}
%    Then it defines the macro \verb+\process@envbody+ which is
%    called when the \verb+\end+ command was successfully scanned.
%    It will insert the scanned text as argument to the macro that
%    is the argument to \verb+\collect@body+.
%    \begin{macrocode}
  \def\process@envbody{%
    \expandafter#1\expandafter{\the\@envbody}}%
%    \end{macrocode}
%    Finally it calls \verb+\collect@@body+ to perform the scan.
%    But we use a renaming trick described below.
%    \begin{macrocode}
  \expandafter\let\csname\@currenvir\endcsname\collect@@body
  \csname\@currenvir\endcsname}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\collect@@body}
%    \verb+\collect@@body+ takes two arguments: the first will consist
%    of all text up to the next \verb+\end+ command, the second will
%    be the \verb+\end+ command's argument.  Note the underlying
%    assumption: an environment that uses \verb=\collect@@body= cannot
%    have another environment of the same name nested within it.  This
%    assumption is true for the major display alignment macros of the
%    {\tt amstex} option.
%    \begin{macrocode}
\def\collect@@body#1\end#2{%
%    \end{macrocode}
%    This argument is then compared to the name of the current
%    environment.
%    \begin{macrocode}
  \def\@tempa{#2}%
  \ifx\@tempa\@currenvir
%    \end{macrocode}
%    If this is the matching \verb+\end+ the rest of the environment's
%    body is collected and the macro \verb+\xxxxx+ (where `xxxxx' is
%    the name of the current environment) is redefined to process the
%    environment's body using the \verb+\process@envbody+ macro
%    defined in \verb+\collect@body+.  Redefining \verb=\xxxxx= in
%    this way is possible first because we are in a group (from
%    \verb=\begin=\dots\verb=\end=) and second because the
%    environments that call \verb=\collect@@body= cannot be nested, as
%    mentioned above.  And the reason we want to redefine
%    \verb=\xxxxx= is so that the user will get a more understandable
%    error message if they have a mismatched or misspelled end of the
%    environment, for example something like
%    \begin{verbatim}
%      \begin{multline*}
%      ...
%      \end{multline}
%    \end{verbatim}
%    In an earlier implementation the scratch macro \verb=\next= was
%    used instead of \verb=\xxxxx=, and the resulting error message
%    was
%    \begin{verbatim}
%     ! Paragraph ended before \next was complete.
%    \end{verbatim}
%      Now the error message is
%    \begin{verbatim}
%     ! Paragraph ended before \multline* was complete.
%    \end{verbatim}
%
%    \begin{macrocode}
    \addto@envbody{#1}%
    \expandafter\edef\csname\@currenvir\endcsname
      {\noexpand\process@envbody\noexpand\end{\@tempa}}%
%    \end{macrocode}
%    Otherwise the text just read is collected in our token register.
%    \begin{macrocode}
  \else
    \addto@envbody{#1\end{#2}}%
  \fi
%    \end{macrocode}
%    The only thing that remains to be done is to call up
%    \verb+\<currenvir>+.
%    \begin{macrocode}
  \csname\@currenvir\endcsname}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{Simple aligning environments}
%
% \begin{macro}{\aligned}
% \begin{macro}{\aligned@}
% \begin{macro}{\endaligned}
%    The {\tt aligned} environment first checks if an optional
%    argument follows and calls up \verb+\aligned@+ to do the
%    work.
%    \begin{macrocode}
\def\aligned{\RIfM@\else\nonmatherr@{\begin{aligned}}\fi
  \null\,\new@ifnextchar[{\aligned@}{\aligned@[c]}}
%    \end{macrocode}
%    \verb+\aligned@+ is taken nearly unchanged from {\tt amstex.tex}.
%    Depending on its position argument it selects the appropriate
%    type of box.
%    \begin{macrocode}
\def\aligned@[#1]{%
  \if #1t\vtop \else \if#1b\vbox \else \vcenter \fi\fi
  \bgroup
%    \end{macrocode}
%    Then it does a number of initializations.
%    \begin{macrocode}
   \Let@\restore@math@cr
%    \end{macrocode}
%    One of these is the restoration of the default definition
%    of the \verb+\tag+ macro, in case that the {\tt aligned}
%    environment is used inside, e.g., an {\tt gather}
%    environment.
%    \begin{macrocode}
   \default@tag
%    \end{macrocode}
%    Another is to increase the vertical space between rows a bit
%    if used inside of another aligning environment.
%    \begin{macrocode}
   \ifinany@\else\openup\jot\fi
%    \end{macrocode}
%    Finally it starts the alignment itself.
%    \begin{macrocode}
   \ialign\bgroup\hfil\strut@$\m@th\displaystyle{##}$&%
    $\m@th\displaystyle{{}##}$\hfil\crcr}
%    \end{macrocode}
%    The \verb+\endalign+ macro ends the alignment and the enclosing
%    vertical box.
%    \begin{macrocode}
\def\endaligned{\crcr\egroup\egroup}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
%    |\hashtoks@| is used to conceal |#| from \tex/'s scanner at
%    certain inconvenient moments in the construction of some display
%    alignments.
%
%    Maybe this could be replaced with the \verb+\sharp+ mechanism
%    from \LaTeX? [mjd,5-Sep-1994]
%    \begin{macrocode}
\newtoks\hashtoks@
\hashtoks@{#}
%    \end{macrocode}
%
% \begin{macro}{\atcount@}
%    For the {\tt alignat} and {\tt alignedat} environment we need
%    an additional counter to keep track of the columns.
%    \begin{macrocode}
\newcount\atcount@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\doat@}
%    The macro \verb+doat@+ takes as positive number as argument
%    and generates a preamble for an alignment with twice as much
%    columns, alternately being flushright and flushleft.
%    This preamble is stored in the macro \verb+\preamble@@+.
%    \begin{macrocode}
\def\doat@#1{\toks@{\hfil\strut@$\m@th
  \displaystyle{\the\hashtoks@}$&$\m@th\displaystyle
  {{}\the\hashtoks@}$\hfil}%
 \atcount@#1\relax\advance\atcount@\m@ne
 \loop\ifnum\atcount@>\z@\toks@\expandafter{\the\toks@&\hfil$\m@th
  \displaystyle{\the\hashtoks@}$&$\m@th
  \displaystyle{{}\the\hashtoks@}$\hfil}\advance
 \atcount@\m@ne\repeat
 \xdef\preamble@{\the\toks@}\xdef\preamble@@{\preamble@}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\alignedat}
% \begin{macro}{\endalignedat}
%    The definition of \verb+\alignat+ is rather straightforward.
%    Not the use of the \verb+\span+ primitive to expand
%    \verb+\preamble@@+.
%    \begin{macrocode}
\def\alignedat#1{\null\,\vcenter\bgroup\doat@{#1}\Let@
 \restore@math@cr\default@tag
 \ifinany@\else\openup\jot\fi\ialign\bgroup\span\preamble@@\crcr}
%    \end{macrocode}
%    \verb+\endalignedat+ has exactly the same task as
%    \verb+\endaligned+.
%    \begin{macrocode}
\let\endalignedat =\endaligned
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\gathered}
% \begin{macro}{\endgathered}
%    Again, \verb+\gather+ and \verb+\endgather+ do not present
%    any new mysteries.
%    \begin{macrocode}
\def\gathered{\RIfM@\else\nonmatherr@{\begin{gathered}}\fi
 \null\,\vcenter\bgroup\Let@\restore@math@cr
 \ifinany@\else\openup\jot\fi\ialign
 \bgroup\hfil\strut@$\m@th\displaystyle{##}$\hfil\crcr}

\let\endgathered =\endaligned
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%
% \subsubsection{The {\tt align} environment}
%
% We start by discussing the special versions of \verb+\tag+ and
% \verb+\math@cr@@@+ to be used within the {\tt align} environments.
% \begin{macro}{\tag@in@align}
%    The \verb+\tag+ command may only appear once in a row of
%    an alignment.  Therefore we first check the switch \verb+tag@+
%    that is set to false at the begin of every row.
%    If this switch is true a \verb+\tag+ was already given in this
%    row and we define \verb+\next@+ to expand to a call to
%    \verb+\invalid@tag+.
%    \begin{macrocode}
\def\tag@in@align{\relax
  \iftag@\DN@{\invalid@tag{Multiple \string\tag}}\else
%    \end{macrocode}
%    Otherwise we set the \verb+tag@+ switch.  But there is more to
%    be done: we must also prevent the automatic generation of a
%    tag.  Therefore we also reset the \verb+@eqnsw+.
%    \begin{macrocode}
   \global\tag@true
   \if@eqnsw\global\@eqnswfalse\fi
%    \end{macrocode}
%    Within a row of an {\tt align} environment the \verb+\tag+
%    command must not typeset the tag immediately since its
%    position can be determined only later.
%    Therefore we use the \verb+\make@df@tag+ macro defined
%    earlier.
%    Finally we call up \verb+\next@+ to process the argument
%    that follows.
%    \begin{macrocode}
   \let\next@\make@df@tag\fi
  \next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\math@cr@@@align}
%    To understand this macro you have to know how an {\tt align}
%    environment is typeset: it has three columns, the first two
%    used for the alignment itself, the last for the tag if there is
%    one.  If not all columns are used \verb+\math@cr@@@align+ has
%    to insert a suitable number of \verb+&+ tokens to put the tag
%    into the third column.
%    This is necessary if either the \verb+@eqnsw+ or the \verb+tag@+
%    switch are set.  To avoid a number of checks we also set the
%    \verb+tag@+ switch when the \verb+@eqnsw+ switch is set.
%    \begin{macrocode}
\def\math@cr@@@align{%
  \if@eqnsw\global\tag@true\fi
%    \end{macrocode}
%    This allows us to check only the \verb+tag@+ switch.
%    \begin{macrocode}
  \iftag@
%    \end{macrocode}
%    The \verb+\and@+ counter is set to zero at the beginning of every
%    row and incremented by one for every column.  This keeps track
%    of the number of \verb+&+ tokens already encountered.
%    Depending of this value we define \verb+\next@+ to expand to
%    the missing \verb+&+ tokens and call it.
%    \begin{macrocode}
   \ifcase\and@
    \DN@{&&}\else
    \DN@{&}\fi\else
    \let\next@\relax\fi
  \next@
%    \end{macrocode}
%    Now we are ready to typeset the tag.  We have to check to
%    \verb+@eqnsw+ once again, to find out if the tag was specified
%    in a \verb+\tag+ command or is to be generated automatically
%    using the {\tt equation} counter.
%    In the former case we use the tag recorded in the \verb+\df@tag+
%    macro, in the latter we also step the {\tt equation} counter.
%    But before we insert a \verb+\relax+ to prevent \TeX{} from
%    scanning too far after a \verb+&+ token.
%    \begin{macrocode}
  \relax
  \if@eqnsw\tagform@\theequation\stepcounter{equation}\else
  \iftag@\df@tag\fi\fi
  \global\@eqnswtrue\cr}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\Tag@}
%    This macro helps to keep things straight if the user typed more
%    than one \verb+&+. It will be called in the third column of the
%    alignment. Since this column is only used for the tag it is an
%    error to use it otherwise.
%
%    \verb|\Tag@| sets \verb|\iffirstchoice@| to true because this
%    test is used by error messages. Normally \verb|\iffirstchoice@| is
%    false inside of \verb|\measure@| because we don't want counters
%    to be stepped, etc.\ while we are measuring; but the \verb|\Tag@|
%    error message is intended precisely for the measuring case, only.
%    \begin{macrocode}
\def\Tag@{\relax\iftag@\else\firstchoice@true
  \PackageError{amstex}{%
  Extra & on this line%
  }{\the\andhelp@% "An extra & here is disastrous"
}\fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\lwidth@}
% \begin{macro}{\rwidth@}
% \begin{macro}{\maxlwidth@}
% \begin{macro}{\maxrwidth@}
% \begin{macro}{\totwidth@}
%    \begin{macrocode}
\newdimen\lwidth@
\newdimen\rwidth@
\newdimen\maxlwidth@
\newdimen\maxrwidth@
\newdimen\totwidth@
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\measure@}
%    \verb+\measure@+ is one of the most important macros of
%    the code that implements the {\tt align} environment.
%    It processes the whole alignment, only to determine the widths
%    of the columns.  For this purpose it uses the following
%    \meta{dimen} registers: \verb+\lwidth@+ and \verb+\rwidth@+
%    for the width of the left and right columns of the current
%    row, \verb+\maxlwidth@+ and \verb+\maxrwidth@+ for the maximum
%    of the widths in the columns processed so far.
%    To keep track of the current column it uses the \verb+\and@+
%    counter.
%    \begin{macrocode}
\def\measure@#1{\lwidth@\z@\rwidth@\z@\maxlwidth@\z@\maxrwidth@\z@
 \global\and@\z@
%    \end{macrocode}
%    The alignment is gathered in a \meta{box} register that will
%    be thrown away afterwards.
%    \begin{macrocode}
 \setbox\@ne\vbox{%
%    \end{macrocode}
%    We start with some initializations:
%    \verb+\everycr+ is set so that the {\tt tag} switch is reset
%    and the \verb+\and@+ counter set to zero at the beginning
%    of every column.  \verb+\Let@+ is called to define \verb+\\+,
%    and the \verb+\tag+ macro is defined to gobble its argument.
%    Finally the \verb+firstchoice@+ switch is reset to prevent
%    the stepping of counters, processing of labels, etc.
%    \begin{macrocode}
   \everycr{\noalign{\global\tag@false\global\and@\z@}}\Let@
   \let\tag\gobble@tag
%    \end{macrocode}
%
%    We also change \verb|\notag| and \verb|\nonumber| while
%    measuring, because their change of the global switch
%    \verb|\if@eqnsw| could have side effects (and did, in version
%    1.0, if \verb|\notag| was used on the last line of an {\tt align}
%    environment).
%    \begin{macrocode}
   \let\notag\@empty \let\nonumber\@empty
   \firstchoice@false
%    \end{macrocode}
%    Now we are ready to do the alignment.
%    The preamble looks complicated, but is rather straightforward:
%    the material in an entry is gathered in \verb+\box+ register
%    $1$ the width of which is then measured.  The values of
%    the corresponding \verb+\dimen+ registers are then updated.
%    Finally the \verb+\and@+ counter is increased by one.
%    \begin{macrocode}
    \halign{\setboxz@h{$\m@th\displaystyle{\@lign##}$}%
     \global\lwidth@\wdz@
     \ifdim\lwidth@>\maxlwidth@\global\maxlwidth@\lwidth@\fi
     \global\advance\and@\@ne
     &\setboxz@h{$\m@th\displaystyle{{}\@lign##}$}%
     \global\rwidth@\wdz@
     \ifdim\rwidth@>\maxrwidth@\global\maxrwidth@\rwidth@\fi
     \global\advance\and@\@ne
%    \end{macrocode}
%    In the third column the \verb+\Tag@+ macro is called to produce
%    an error message if the user tries to put more than one \verb+&+
%    in a row (or forgets the \verb|\\| command at the end of a row).
%    The material in this column is simply thrown away.
%    \begin{macrocode}
     &\Tag@\@gobble{##}\crcr#1\crcr}}%
%    \end{macrocode}
%    Finally we set \verb+\totwidth@+ to the sum of \verb+\maxlwidth@+
%    and \verb+\maxrwidth@+.
%    This will be used later to determine the vertical position of
%    the tags.
%    \begin{macrocode}
 \totwidth@\maxlwidth@\advance\totwidth@\maxrwidth@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\displ@y}
% \begin{macro}{\displ@y@}
%    The macro \verb+\displ@y+ was copied from the {\tt plain.tex}
%    file, and then \verb+\interdisplaylinepenalty+ was changed to
%    \verb+\@eqpen+.
%    \begin{macrocode}
\def\displ@y{\global\dt@ptrue\openup\jot\m@th
  \everycr{\noalign{\ifdt@p \global\dt@pfalse
      \vskip-\lineskiplimit \vskip\normallineskiplimit
      \else \penalty\@eqpen \fi}}}
%    \end{macrocode}
%    \verb+\displ@y@+ is nearly the same; it additionally
%    sets the \verb+tag@+ switch and the \verb+\and@+ and
%    \verb+\dspbrk@lvl+ counters to their default values.
%    \begin{macrocode}
\def\displ@y@{\global\dt@ptrue\openup\jot
  \everycr{\noalign{\global\tag@false
                   \global\and@\z@
                   \global\dspbrk@lvl\m@ne
                   \ifdt@p\global\dt@pfalse
      \vskip-\lineskiplimit\vskip\normallineskiplimit\else
      \penalty\@eqpen\fi}}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\black@}
%    This macro is made to produce an overfull box message and
%    possibly (depending on the value of \verb+\overfullrule+)
%    a rule in the margin if the total width of an alignment
%    is larger than the value of \verb+\displaywidth+.
%    \begin{macrocode}
\def\black@#1{\noalign{\ifdim#1>\displaywidth
 \dimen@\prevdepth\nointerlineskip
 \vskip-\ht\strutbox@\vskip-\dp\strutbox@
 \vbox{\noindent\hbox to#1{\strut@\hfill}}%
 \prevdepth\dimen@
 \fi}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\align}
%     The {\tt align} environment may appear at two different places:
%     inside of a {\tt gather} environment or in outer paragraph mode.
%     These two cases may be distinguished easily by checking the
%     \verb+ingather@+ switch.
%    \begin{macrocode}
\def\align{\ifingather@
%    \end{macrocode}
%    The version of \verb+\align+ to be used
%    inside {\tt gather} is called \verb+\align (in \gather)+.
%    We define \verb+\next@+ to call this macro.
%    But before we have to insert a special brace to hide the
%    \verb+&+ in the body of the align environment from \TeX{}'s
%    scanning mechanism.
%    \begin{macrocode}
  {\ifnum0=`}\fi
  \DN@{\@nameuse{align (in \string\gather)}}%
%    \end{macrocode}
%    Otherwise we proceed by first checking if we are in the right
%    mode.  If not we define \verb+\next@+ to make the
%    \verb+\endalign+ macro a no-op and to throw away its
%    argument.  The reason for this will become clear below.
%    \begin{macrocode}
  \else \ifmmode\nomath@env
    \DN@{\let\endalign\relax\@gobble}\else
%    \end{macrocode}
%    Now we can safely start the display math mode and do the
%    appropriate initializations.  We define \verb+\next@+ to
%    be \verb+\align@+ which is the internal macro that processes
%    the body of a top-level {\tt align} environment.
%    \begin{macrocode}
  $$\stepcounter{equation}%
  \st@rredfalse\let\next@\align@\fi\fi
%    \end{macrocode}
%    Finally we scan the environments body and call \verb+\next@+
%    on it.  The definition of \verb+\next@+ in the invalid case
%    above is made to recover most gracefully from the error by
%    skipping the whole environment.
%    \begin{macrocode}
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\align*}
%    The \verb+\align*+ macro is defined analogously to
%    \verb+align+.
%    \begin{macrocode}
\@namedef{align*}{\ifingather@
  {\ifnum0=`}\fi
  \DN@{\@nameuse{align* (in \string\gather)}}\else
   \ifmmode\nomath@env
    \DN@{\@namedef{endalign*}{}\@gobble}\else
   $$\st@rredtrue
  \let\next@\align@\fi\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\lineht@}
%     The dimen register \verb+\lineht@+ is used to keep track
%     of the height of a row in an alignment.
%     \begin{macrocode}
\newdimen\lineht@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\align@}
%    The definition of the \verb+\align@+ macro is now rather
%    straightforward.  After setting the switches and doing
%    the initializations we call up either \verb*+\align + or
%    \verb*+\align  +, depending on whether the tags should be
%    typeset to the left or to the right.
%    \begin{macrocode}
\def\align@{\inalign@true\inany@true
 \displaybreak@\intertext@
 \let\math@cr@@@\math@cr@@@align
 \let\tag\tag@in@align
 \global\and@\z@\global\dspbrk@lvl\m@ne
 \iftagsleft@\DN@{\@nameuse{align }}\else
  \DN@{\@nameuse{align \space}}\fi\next@}
%    \end{macrocode}
% \end{macro}
%
%    (Internal note: Beginning here, numerous changes have been made
%    by David M. Jones to implement the \opt{fleqn} option and the
%    \cn{adjusttag} command.  The changes to \cs{align\space} are
%    typical, so they have been described in some detail.  Later, I'll
%    only describe new types of changes.)
%
% \begin{macro}{\align\space}
%    \begin{macrocode}
\@namedef{align }#1{%
    \measure@{#1}%
    \global\and@\z@
    \global\dspbrk@lvl\m@ne
%    \end{macrocode}
%    DMJ: \cs{totwidth@} is the width of the longest line of the
%    display, as calculated by \cs{measure@} above, and is used to
%    determine whether the equation will result in an overfull hbox.
%    However, if the flushleft style is being used, this should be
%    incremented by \cs{@mathmargin}, since the left margin is fixed.
%    \begin{macrocode}
    \if@fleqn %%*F
        \advance\totwidth@\@mathmargin %%*F
    \fi %%*F
    \ifdim\totwidth@>\displaywidth
        \let\displaywidth@\totwidth@
    \else
        \let\displaywidth@\displaywidth
    \fi
    \ifingather@
        \everycr{%
            \noalign{%
                \global\and@\z@
                \global\dspbrk@lvl\m@ne
            }%
        }%
    \else
        \displ@y@
    \fi
    \Let@
    \ifst@rred\else\@seteqlabel\theequation\fi
%    \end{macrocode}
%    DMJ: The initial \cs{tabskip} is set to \cs{@mathmargin}, rather
%    than the hardcoded value of \cs{@centering} that was used
%    previously.
%    \begin{macrocode}
    \tabskip\@mathmargin %%*F
%    \end{macrocode}
%    DMJ: Normally, the \cs{halign} that makes up the \cs{align}
%    should be typesset to a width of \cs{displaywidth}.  However, if
%    the \cs{align} is used inside of a \cs{gather} when \opt{fleqn}
%    is in force, the \cs{align} will be shifted to the right by
%    \cs{@mathmargin}, since the enclosing \cs{gather} will itself
%    start with a \cs{tabskip} of \cs{@mathmargin}.  So, if the
%    \cs{align} is inside a \cs{gather}, we set the \cs{align}'s
%    initial \cs{tabskip} to zero, and decrease the width of the
%    \cs{align} by \cs{@mathmargin}.
%    \begin{macrocode}
    \dimen@\displaywidth %%*F
    \if@fleqn %%*F
        \ifingather@ %%*F
            \tabskip\z@skip %%*F
            \advance\dimen@-\@mathmargin %%*F
        \fi %%*F
    \fi %%*F
    \halign to\dimen@\bgroup %%*F
        \ifst@rred\nonumber\fi
        \hfil
        \strut@
        \setboxz@h{\global\tag@false$\m@th\displaystyle{\@lign##}$}%
        \global\lwidth@\wdz@
        \global\lineht@\ht\z@
        \boxz@
        \global\advance\and@\@ne
        \tabskip\z@skip
       &\setboxz@h{$\m@th\displaystyle{{}\@lign##}$}%
        \global\rwidth@\wdz@
        \ifdim\ht\z@>\lineht@
            \global\lineht@\ht\z@
        \fi
        \boxz@
        \hfil
        \global\advance\and@\@ne
        \tabskip\@centering
       &\kern-\displaywidth@
        \setboxz@h{\@lign\strut@{##}}%
%    \end{macrocode}
%    DMJ: If \opt{fleqn} is in force,, the calculation of how much
%    space is left for the equation tag needs to be modified in a
%    fairly obvious way.
%    \begin{macrocode}
        \if@fleqn %%*F
            \dimen@\@mathmargin %%*F
            \advance\dimen@\maxlwidth@ %%*F
            \advance\dimen@-\lwidth@ %%*F
        \else %%*F
            \dimen@\displaywidth
            \advance\dimen@-\totwidth@
            \divide\dimen@\tw@
            \advance\dimen@\maxlwidth@
            \advance\dimen@-\lwidth@
        \fi %%*F
        \ifdim\dimen@<\tw@\wdz@
            \rlap{\vbox{\normalbaselines\boxz@\vbox to\lineht@{}}}%
        \else
            \rlap{\boxz@}%
        \fi
        \tabskip\displaywidth@
        \crcr
        #1%
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\align\space\space}
%    \begin{macrocode}
\@namedef{align \space}#1{%
    \measure@{#1}%
    \if@fleqn %%*F
        \advance\totwidth@\@mathmargin %%*F
    \fi %%*F
    \global\and@\z@
    \global\dspbrk@lvl\m@ne
    \ifingather@
        \everycr{\noalign{\global\and@\z@\global\dspbrk@lvl\m@ne}}%
    \else
        \displ@y@
    \fi
    \Let@
    \ifst@rred\else\@seteqlabel\theequation\fi
    \tabskip\@mathmargin %%*F
    \dimen@\displaywidth %%*F
    \if@fleqn %%*
        \ifingather@ %%*F
            \tabskip\z@skip %%*F
            \advance\dimen@-\@mathmargin %%*F
        \fi %%*F
    \fi %%*F
     \halign to\dimen@\bgroup %%*F
        \ifst@rred\nonumber\fi
        \hfil
        \strut@
        \setboxz@h{\global\tag@false$\m@th\displaystyle{\@lign##}$}%
        \global\lwidth@\wdz@\boxz@
        \global\advance\and@\@ne
        \tabskip\z@skip
       &\setboxz@h{$\m@th\displaystyle{{}\@lign##}$}%
        \global\rwidth@\wdz@
        \boxz@
%    \end{macrocode}
%    DMJ: Miscellaneous question: Is the following line a typo?  Why
%    not \cs{hfil}, as in the corresponding line in
%    \verb+\@nameuse{align }+?
%    \begin{macrocode}
        \hfill
        \global\advance\and@\@ne
        \tabskip\@centering
       &\setboxz@h{\@lign\strut@{##}}%
        \dimen@\displaywidth
        \advance\dimen@-\totwidth@
        \divide\dimen@\tw@
        \advance\dimen@\maxrwidth@
        \advance\dimen@-\rwidth@
        \ifdim\dimen@<\tw@\wdz@
%    \end{macrocode}
%    DMJ: \cs{@movetag} will take care of any vertical adjustment
%    requested by \adjusttag.
%    \begin{macrocode}
            \llap{\vtop{\@movetag\normalbaselines\null\boxz@}}%%*T
        \else
            \llap{\boxz@}%
        \fi
        \tabskip\z@skip
        \crcr#1%
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endalign}
% \begin{macro}{\endalign*}
%    (Internal remark: should \verb+\endalign+ set
%    \verb+\postdisplaypenalty+ according to the
%     value of \verb+\dspbrk@lvl+?)
%    \begin{macrocode}
\def\endalign{\math@cr@@@align
  \black@\totwidth@
  \egroup$$\global\@ignoretrue\setb@ck}

\@namedef{endalign*}{\math@cr@@@align\black@\totwidth@
  \egroup$$\global\@ignoretrue}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\align\space (in \string\gather)}
%    \begin{macrocode}
\@namedef{align (in \string\gather)}{%
  \ifst@rred\stepcounter{equation}\fi
  \def\endalign{\@nameuse{endalign (in \string\gather)}\ifnum0=`{\fi}}%
  \vcenter\bgroup\st@rredfalse
    \collect@body\align@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endalign\space (in \string\gather)}
%    \begin{macrocode}
\@namedef{endalign (in \string\gather)}{%
  \math@cr@@@align\black@\totwidth@
  \egroup\egroup
  \ifst@rred\setb@ck\fi% this ifst@rred is set by the enclosing gather
  \global\tag@false\global\@eqnswfalse}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\align* (in \string\gather)}
%    \begin{macrocode}
\@namedef{align* (in \string\gather)}{%
  \@namedef{endalign*}{\@nameuse{endalign* (in \string\gather)}%
                       \ifnum0=`{\fi}}%
  \vcenter\bgroup\st@rredtrue
    \collect@body\align@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endalign* (in \string\gather)}
%    \begin{macrocode}
\@namedef{endalign* (in \string\gather)}{%
  \math@cr@@@align\black@\totwidth@\egroup\egroup
  \global\tag@false\global\@eqnswfalse}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{The {\tt alignat} environment}
%
% \begin{macro}{\ifxat@}
%    \begin{macrocode}
\newif\ifxat@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\alignat}
%    \begin{macrocode}
\def\alignat#1{%
 \ifmmode\nomath@env\DN@{\let\endalignat\relax\@gobble}\else$$%
 \st@rredfalse\stepcounter{equation}\@seteqlabel\theequation
 \DN@{\@nameuse{alignat }#1}\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\alignat*}
%    \begin{macrocode}
\@namedef{alignat*}#1{%
 \ifmmode\nomath@env\DN@{\@namedef{endalignat*}{}\@gobble}\else$$%
 \st@rredtrue
 \DN@{\@nameuse{alignat }#1}\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ifmeasuring@}
%    \begin{macrocode}
\newif\ifmeasuring@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\savealignat@}
%    \begin{macrocode}
\newbox\savealignat@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\math@cr@@@alignat}
%    \begin{macrocode}
\def\math@cr@@@alignat{%
  \if@eqnsw\global\tag@true\fi
  \iftag@
   \multiply\count@\tw@
   \xdef\next@{}\loop\ifnum\count@>\and@\xdef\next@{&\next@}%
    \advance\count@\m@ne\repeat\else
   \let\next@\relax\fi
  \next@
  \relax
  \if@eqnsw\tagform@\theequation\stepcounter{equation}\else
  \iftag@\df@tag\fi\fi
  \global\@eqnswtrue\cr}%
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\alignat\space}
%    \begin{macrocode}
\@namedef{alignat }#1#2{%
    \inany@true
    \xat@false
    \let\tag\tag@in@align
    \def\math@cr@@@{\count@#1\relax \math@cr@@@alignat}%
    \displaybreak@
    \intertext@
    \displ@y@
    \ifst@rred
        \global\@eqnswfalse
    \else
        \global\@eqnswtrue
    \fi
    \measuring@true
    \setbox\savealignat@\hbox{%
        $\m@th\displaystyle\Let@
        \attag@{#1}%
        \vbox{\firstchoice@false\halign{\span\preamble@@\crcr#2\crcr}}$%
    }%
    \measuring@false
    \Let@
    \attag@{#1}%
    \tabskip\@mathmargin %%*F
    \halign to\displaywidth\bgroup
        \span\preamble@@\crcr
        #2%
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endalignat}
%    \begin{macrocode}
\def\endalignat{\math@cr@@@\black@{\wd\savealignat@}%
     \egroup\setb@ck$$\global\@ignoretrue}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endalignat*}
%    \begin{macrocode}
\@namedef{endalignat*}{\math@cr@@@\black@{\wd\savealignat@}\egroup
  $$\global\@ignoretrue}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{The {\tt xalignat} environment}
%
% \begin{macro}{\xalignat}
%    \begin{macrocode}
\def\xalignat#1{%
 \ifmmode\nomath@env\DN@{\let\endxalignat\relax\@gobble}\else$$%
 \st@rredfalse\stepcounter{equation}\@seteqlabel\theequation
 \DN@{\@nameuse{xalignat }#1}\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\xalignat*}
%    \begin{macrocode}
\@namedef{xalignat*}#1{%
 \ifmmode\nomath@env\DN@{\@namedef{endxalignat*}{}\@gobble}\else$$%
 \st@rredtrue
 \DN@{\@nameuse{xalignat }#1}\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endxalignat}
% \begin{macro}{\endxalignat*}
%    \begin{macrocode}
\let\endxalignat=\endalignat

\expandafter\let\csname endxalignat*\expandafter
  \endcsname\csname endalignat*\endcsname
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\xalignat\space}
%    \begin{macrocode}
\@namedef{xalignat }#1#2{%
    \inany@true
    \xat@true
    \let\tag\tag@in@align
    \def\math@cr@@@{\count@#1\relax\math@cr@@@alignat}%
    \displaybreak@
    \intertext@
    \displ@y@
    \measuring@true
    \setbox\savealignat@\hbox{%
        $\m@th\displaystyle\Let@
        \attag@{#1}%
        \vbox{%
            \firstchoice@false
            \halign{\span\preamble@@\crcr#2\crcr}%
        }%
        $%
    }%
    \measuring@false
    \Let@
    \attag@{#1}%
    \tabskip\@mathmargin %%*F
    \halign to\displaywidth\bgroup
        \span\preamble@@\crcr#2%
}
%    \end{macrocode}
% \end{macro}
%
%    Bug: xalignat* did not suppress numbers. Fix [mjd,1994/10/11]: Take
%    out \cs{ifst@rred} reference in \cs{xalignat\char`\ } and move it
%    to the beginning of the halign preamble (in \cs{attag@}); the
%    \cn{nonumber} function needs to be executed at the beginning of
%    every line if the \cs{ifst@rred} switch is true.
% \begin{macro}{\attag@}
%    \begin{macrocode}
\def\attag@#1{%
 \let\TAG@\Tag@\let\Tag@0%
 \ifmeasuring@\def\llap@##1{\setboxz@h{##1}\hbox to\tw@\wdz@{}}%
  \def\rlap@##1{\setboxz@h{##1}\hbox to\tw@\wdz@{}}\else
  \let\llap@\llap\let\rlap@\rlap\fi
 \toks@{\hfil\strut@$\m@th\displaystyle{\@lign\the\hashtoks@}$%
  \tabskip\z@skip
  \global\advance\and@\@ne
  &$\m@th\displaystyle{{}\@lign\the\hashtoks@}$\hfil
  \ifxat@\tabskip\@centering\fi\global\advance\and@\@ne}%
 \iftagsleft@
  \@temptokena{\tabskip\@centering&\Tag@\kern-\displaywidth
   \rlap@{\@lign
     \the\hashtoks@
    }%
   \global\advance\and@\@ne\tabskip\displaywidth}\else
  \@temptokena{\tabskip\@centering&\Tag@\llap@{\@lign
   \the\hashtoks@
  }\global\advance\and@\@ne\tabskip\z@skip}\fi
 \atcount@#1\relax\advance\atcount@\m@ne
 \loop\ifnum\atcount@>\z@
 \toks@\expandafter{\the\toks@&\hfil$\m@th\displaystyle{\@lign
  \the\hashtoks@}$\global\advance\and@\@ne
  \tabskip\z@skip
  &$\m@th\displaystyle{{}\@lign\the\hashtoks@}$\hfil\ifxat@
  \tabskip\@centering\fi\global\advance\and@\@ne}\advance\atcount@\m@ne
 \repeat
 \xdef\preamble@{\the\toks@\the\@temptokena}%
 \xdef\preamble@@{\ifst@rred\noexpand\nonumber\fi\preamble@}%
 \let\Tag@\TAG@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\xxalignat}
%    \begin{macrocode}
\def\xxalignat#1{%
 \ifmmode\nomath@env\DN@{\let\endxxalignat\relax\@gobble}\else$$%
 \DN@{\@nameuse{xxalignat }#1}\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\xxalignat\space}
%    \begin{macrocode}
\@namedef{xxalignat }#1#2{\inany@true
 \displaybreak@\intertext@
 \displ@y\setbox\savealignat@\hbox{$\m@th\displaystyle\Let@
 \xxattag@{#1}%
 \vbox{\firstchoice@false\halign{\span\preamble@@\crcr#2\crcr}}$}%
 \Let@\xxattag@{#1}\tabskip\z@skip\halign to\displaywidth\bgroup
  \span\preamble@@\crcr#2}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endxxalignat}
%    \begin{macrocode}
\expandafter\let\expandafter\endxxalignat\csname endxalignat*\endcsname
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\xxattag@}
%    \begin{macrocode}
\def\xxattag@#1{\toks@{\tabskip\z@skip\hfil\strut@
 $\m@th\displaystyle{\the\hashtoks@}$&%
 $\m@th\displaystyle{{}\the\hashtoks@}$\hfil\tabskip\@centering&}%
 \atcount@#1\relax\advance\atcount@\m@ne\loop\ifnum\atcount@>\z@
 \toks@
  \expandafter
   {\the\toks@&\hfil$\m@th\displaystyle{\the\hashtoks@}$%
  \tabskip\z@skip&$\m@th\displaystyle{{}\the\hashtoks@}$\hfil
  \tabskip\@centering}\advance\atcount@\m@ne\repeat
 \xdef\preamble@{\the\toks@\tabskip\z@skip}\xdef\preamble@@{\preamble@}}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{The {\tt gather} environment}
%
% \begin{macro}{\gwidth@}
% \begin{macro}{\gmaxwidth@}
%    \begin{macrocode}
\newdimen\gwidth@
\newdimen\gmaxwidth@
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\gmeasure@}
%    \begin{macrocode}
\def\gmeasure@#1{\gwidth@\z@\gmaxwidth@\z@\setbox\@ne\vbox{\Let@
 \firstchoice@false\let\tag\gobble@tag
 \halign{\setboxz@h{$\m@th\displaystyle{##}$}\global\gwidth@\wdz@
 \ifdim\gwidth@>\gmaxwidth@\global\gmaxwidth@\gwidth@\fi
 &\@gobble{##}\crcr#1\crcr}}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\math@cr@@@gather}
%    \begin{macrocode}
\def\math@cr@@@gather{%
  \if@eqnsw\global\tag@true\fi
  \iftag@
    \DN@{&\relax \if@eqnsw
                    \tagform@\theequation \stepcounter{equation}%
                 \else\iftag@\df@tag\fi\fi}%
  \else
    \expandafter\@gobble\fi
  \next@
  \global\@eqnswtrue\cr}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\gather}
%    \begin{macrocode}
\def\gather{%
 \ifmmode\nomath@env\DN@{\let\endgather\relax\@gobble}\else $$%
  \ingather@true\inany@true
  \stepcounter{equation}%
  \let\tag\tag@in@align\st@rredfalse
  \displaybreak@\intertext@
  \displ@y
  \Let@\@seteqlabel\theequation
  \let\math@cr@@@\math@cr@@@gather
  \iftagsleft@\DN@{\@nameuse{gather }}\else
   \DN@{\@nameuse{gather \space}}\fi\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\gather*}
%    \begin{macrocode}
\@namedef{gather*}{%
 \ifmmode\nomath@env\DN@{\@namedef{endgather*}{}\@gobble}\else $$%
  \ingather@true\inany@true
  \let\tag\tag@in@align\st@rredtrue
  \displaybreak@\intertext@
  \displ@y\Let@
  \let\math@cr@@@\math@cr@@@gather
  \iftagsleft@\DN@{\@nameuse{gather }}\else
   \DN@{\@nameuse{gather \space}}\fi\fi
 \collect@body\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\glineht@}
%    \begin{macrocode}
\newdimen\glineht@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\gather\space\space}
% After using \verb;\gmeasure@; we need to again
% \verb;\dt@ptrue;.  (If not then we get
% \verb;\penalty\@eqpen; before the first line, which could
% allow an undesired page break.)
%    \begin{macrocode}
\@namedef{gather \space}#1{%
    \gmeasure@{#1}%
    \if@fleqn %%*F
        \advance\gmaxwidth@\@mathmargin %%*F
    \fi %%*F
    \global\dt@ptrue
    \tabskip\@mathmargin %%*F
    \halign to\displaywidth\bgroup
        \ifst@rred\nonumber\else\global\@eqnswtrue\fi
%    \end{macrocode}
%    DMJ: If we're doing flush left equations, we don't want any extra
%    glue here.
%    \begin{macrocode}
        \if@fleqn\else\hfil\fi %%*F
        \strut@
        \setboxz@h{\global\tag@false$\m@th\displaystyle{##}$}%
        \global\gwidth@\wdz@\boxz@
        \hfil
%    \end{macrocode}
%    DMJ: We need to explicitly set \cs{tabskip} back to
%    \cs{@centering} here, since it no longer inherits that value from
%    the \cs{tabskip} set above.
%    \begin{macrocode}
        \tabskip\@centering %%*F
       &\setboxz@h{\strut@{##}}%
        \dimen@\displaywidth
        \advance\dimen@-\gwidth@
        \if@fleqn %%*F
            \advance\dimen@-\@mathmargin %%*F
        \else %%*F
%    \begin{macrocode}
%    DMJ: I've fixed a bug here in the algorithm used by \cn{gather}
%    for deciding when equation tags should be put on a separate line:
%    The previous algorithm only checked to see if there was space for
%    the label itself, rather than seeing if there was twice as much
%    space as the label takes up.  The solution is to divide the
%    currently calculated distance by 2.  (This is, naturally, not
%    backwards compatible.)
%    \end{macrocode}
            \divide\dimen@\tw@ %%*B
        \fi %%*F
        \ifdim\dimen@<\tw@\wdz@ %%*
            \llap{\vtop{\@movetag\normalbaselines\null\boxz@}}%%*T %%*
        \else
            \llap{\boxz@}% %%*
        \fi
        \tabskip\z@skip
        \crcr
        #1%
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endgather}
% \begin{macro}{\endgather*}
%    \begin{macrocode}
\def\endgather{\math@cr@@@
  \black@\gmaxwidth@\egroup $$\setb@ck\global\@ignoretrue}

\@namedef{endgather*}{\math@cr@@@
  \black@\gmaxwidth@\egroup $$\global\@ignoretrue}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\gather\space}
%    \begin{macrocode}
\@namedef{gather }#1{%
    \gmeasure@{#1}%
    \global\dt@ptrue
    \if@fleqn %%*F
        \advance\gmaxwidth@\@mathmargin %%*F
    \fi %%*F
    \ifdim\gmaxwidth@>\displaywidth
        \let\gdisplaywidth@\gmaxwidth@
    \else
        \let\gdisplaywidth@\displaywidth
    \fi
    \tabskip\@mathmargin %%*F
    \halign to\displaywidth\bgroup
        \ifst@rred\nonumber\else\global\@eqnswtrue\fi
        \if@fleqn\else\hfil\fi %%*F
        \strut@
        \setboxz@h{\global\tag@false$\m@th\displaystyle{##}$}%
        \global\gwidth@\wdz@
        \global\glineht@\ht\z@
        \boxz@
        \hfil
        \tabskip\@centering %%*F
       &\kern-\gdisplaywidth@
        \setboxz@h{\strut@{##}}%
        \if@fleqn %%*F
            \dimen@\@mathmargin %%*F
        \else %%*F
            \dimen@\displaywidth
            \advance\dimen@-\gwidth@
%     \end{macrocode}
%     Another instance of the non-backwards compatible bug fix
%     mentioned above.
%     \begin{macrocode}
            \divide\dimen@\tw@ %%*B
        \fi %%*F
        \ifdim\dimen@<\tw@\wdz@ %%*
            \rlap{\vbox{\normalbaselines\boxz@\vbox to\glineht@{}}}% %%*
        \else
            \rlap{\boxz@}% %%*
        \fi
        \tabskip\gdisplaywidth@
        \crcr
        #1%
}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection {The {\tt split} environment}
%
% \begin{macro}{\split}
%    \begin{macrocode}
\def\split{%
 \ifinany@\let\next@\insplit@\else
  \DN@{\PackageError{amstex}{\string\begin{split} is not allowed
    here.  Try the `aligned' environment.}\@ehb}\fi
 \next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\insplit@}
%    \begin{macrocode}
\def\insplit@{\global\setbox\z@\vbox\bgroup
  \Let@ \restore@math@cr \default@tag % disallow use of \tag here
  \ialign\bgroup \hfil\strut@
   $\m@th\displaystyle{##}$&$\m@th\displaystyle{{}##}$\hfill\crcr}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endsplit}
%    \begin{macrocode}
\def\endsplit{\crcr\egroup\egroup
 \iftagsleft@\expandafter\lendsplit@\else
  \expandafter\rendsplit@\fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\rendsplit@}
%    \begin{macrocode}
\def\rendsplit@{\global\setbox9 \vbox
 {\unvcopy\z@\global\setbox8 \lastbox\unskip}%
 \setbox\@ne\hbox{\unhcopy8 \unskip\global\setbox\tw@\lastbox
 \unskip\global\setbox\thr@@\lastbox}%
 \global\setbox7 \hbox{\unhbox\tw@\unskip}%
 \ifinalign@\ifctagsplit@
  \gdef\split@{\hbox to\wd\thr@@{}&
   \vcenter{\vbox{\moveleft\wd\thr@@\boxz@}}}%
 \else\gdef\split@{&\vbox{\moveleft\wd\thr@@\box9}\crcr
  \box\thr@@&\box7}\fi
 \else
  \ifctagsplit@\gdef\split@{\vcenter{\boxz@}}\else
  \gdef\split@{\box9\crcr\hbox{\box\thr@@\box7}}\fi
 \fi
 \aftergroup\split@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\lendsplit@}
%    \begin{macrocode}
\def\lendsplit@{\global\setbox9\vtop{\unvcopy\z@}%
 \setbox\@ne\vbox{\unvcopy\z@\global\setbox8\lastbox}%
 \setbox\@ne\hbox{\unhcopy8\unskip\setbox\tw@\lastbox
  \unskip\global\setbox\thr@@\lastbox}%
 \ifinalign@\ifctagsplit@
  \gdef\split@{\hbox to\wd\thr@@{}&
  \vcenter{\vbox{\moveleft\wd\thr@@\box9}}}%
  \else
  \gdef\split@{\hbox to\wd\thr@@{}&\vbox{\moveleft\wd\thr@@\box9}}\fi
 \else
  \ifctagsplit@\gdef\split@{\vcenter{\box9}}\else
  \gdef\split@{\box9}\fi
 \fi\aftergroup\split@}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{The {\tt multline} environment}
%
% In the original \AmSTeX{}, \verb=\multlinegap= is a macro with
% an argument that resets an internal dimension (one with an
% @ character in its name).  Here, to save control sequence names,
% we define \verb=\multlinegap= to be the dimension itself and the
% documentation instructs users to use \verb=\setlength= if they
% need to change it.
% \begin{macro}{\multlinegap}
% \begin{macro}{\multlinetaggap@}
%    \begin{macrocode}
\newdimen\multlinegap
\multlinegap10pt
\newdimen\multlinetaggap@
\multlinetaggap@10pt
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%    Remark (21-JUN-1990): If \verb=\tag= is used inside
%    \verb=multline= to override the normal tag, the \verb=\label=
%    doesn't seem to be correctly set.  Need to look into this.
% \begin{macro}{\multline}
%    \begin{macrocode}
\def\multline{%
 \ifmmode\nomath@env\DN@{\let\endmultline\relax\@gobble}%
 \else $$\DN@{\collect@body\multline@}\fi
 \st@rredfalse\@eqnswtrue \@seteqlabel\theequation
 \stepcounter{equation}\next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multline*}
%    \begin{macrocode}
\@namedef{multline*}{%
 \ifmmode\nomath@env\DN@{\@namedef{endmultline*}{}\@gobble}%
 \else $$\DN@{\collect@body\multline@}\fi
 \st@rredtrue\@eqnswfalse \let\@currentlabel\@empty
 \next@}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multline@}
%    The definition of \verb'\tag' here is complicated by the fact that
%    the tag contents are typeset only during the measuring phase, and
%    saved in a box. So we do not want to apply the
%    \verb'\iffirstchoice@' test to the statement that sets back the
%    equation counter. As previously defined (in versions 1.1 and
%    earlier), a \verb'\tag' in a \verb'multline' environment did not
%    properly set the equation counter back to the proper value.
%    [mjd,17-Jan-1994]
%    \begin{macrocode}
\def\multline@{\inany@true\displaybreak@
 \global\tag@false
 \def\tag{\ifst@rred\else
%    Can't use \setb@ck here because its \iffirstchoice@ test is
%    misguided in the multline case.
   \global\advance\c@equation\m@ne\fi\tag@in@align}%
 \iftagsleft@
  \expandafter\lmultline@@\else
  \expandafter\rmultline@@\fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\mwidth@}
%    \begin{macrocode}
\newdimen\mwidth@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\rmeasure@}
%    \begin{macrocode}
\def\rmmeasure@#1{%
 \def\shoveleft##1{##1}\def\shoveright##1{##1}%
 \setbox\@ne\vbox{\firstchoice@false\Let@\halign{\setboxz@h
  {$\m@th\@lign\displaystyle{}##$}\global\mwidth@\wdz@
  \crcr#1\crcr}}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\mlineht@}
%    \begin{macrocode}
\newdimen\mlineht@
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ifzerocr@}
% \begin{macro}{\ifonecr@}
%    \begin{macrocode}
\newif\ifzerocr@
\newif\ifonecr@
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\lmmeasure@}
%    \begin{macrocode}
\def\lmmeasure@#1{\global\zerocr@true\global\onecr@false
 \everycr{\noalign{\ifonecr@\global\onecr@false\fi
  \ifzerocr@\global\zerocr@false\global\onecr@true\fi}}%
  \def\shoveleft##1{##1}\def\shoveright##1{##1}%
 \setbox\@ne\vbox{\Let@\firstchoice@false\halign{\setboxz@h
  {$\m@th\@lign\displaystyle{}##$}\ifonecr@\global\mwidth@\wdz@
  \global\mlineht@\ht\z@\fi\crcr#1\crcr}}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\mtagbox@}
% \begin{macro}{\ltwidth@}
% \begin{macro}{\rtwidth@}
%    \begin{macrocode}
\newbox\mtagbox@
\newdimen\ltwidth@
\newdimen\rtwidth@
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\lmultline@@}
%    \begin{macrocode}
\def\lmultline@@#1{%
    \lmmeasure@{#1}%
    \setbox\mtagbox@\hbox{%
        \iftag@
            \df@tag
        \else
            \if@eqnsw
                \global\tag@true
                \tagform@\theequation
            \fi
        \fi
    }%
    \dimen@\mwidth@
    \advance\dimen@\wd\mtagbox@
    \advance\dimen@\multlinetaggap@
    \if@fleqn %%*F
        \advance\dimen@\@mathmargin %%*F
    \fi %%*F
    \ifdim\dimen@>\displaywidth
        \ltwidth@\z@
    \else
        \ltwidth@\wd\mtagbox@
    \fi
    \lmultline@@@#1
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\lmultline@@}
%    \begin{macrocode}
\def\lmultline@@@{%
    \displ@y
    \def\shoveright##1{##1\hfilneg\hskip\multlinegap}%
%    \end{macrocode}
%    DMJ: In \opt{fleqn} mode, \cn{shoveleft} doesn't need to do
%    anything.  (Question: Are \cs{shoveleft} and \cs{shoveright} even
%    considered supported parts of \AmS-\LaTeX?  I don't think they're
%    in the documentation.)
%
%    DMJ: It's mildly annoying that \cs{shoveleft} and \cs{shoveright}
%    do unreasonable things if used on the first or last line of a
%    \cs{multline}, but I haven't tried to do anything about that.  It
%    might be hard.
%    \begin{macrocode}
    \if@fleqn %%*F
        \def\shoveleft##1{##1}% %%*F
    \else %%*F
        \def\shoveleft##1{%
                \setboxz@h{$\m@th\displaystyle{}##1$}%
                \setbox\@ne\hbox{$\m@th\displaystyle##1$}%
                \hfilneg
                \iftag@
                    \ifdim\ltwidth@>\z@
                        \hskip\ltwidth@
                        \hskip\multlinetaggap@
                    \fi
                \else
                    \hskip\multlinegap
                \fi
                \hskip.5\wd\@ne
                \hskip-.5\wdz@##1%
        }%
    \fi %%*F
%    \end{macrocode}
%    DMJ: It seems like a good idea to initialize \cs{tabskip} to 0
%    here, just in case it's been left with a non-zero value.
%    \begin{macrocode}
    \if@fleqn %%*F
        \tabskip\@mathmargin %%*F
    \else %%*F
        \tabskip\z@skip %%*
    \fi %%*F
%    \end{macrocode}
%    DMJ: In \opt{fleqn} mode, effective width of the display is
%    $\cs{displaywidth} - \cs{@mathmargin}$, so that's how wide the
%    \cs{hbox} in the preamble should be.  I'll reuse \cs{totwidth@}
%    here to do the calculation since an align can't occur inside a
%    \cs{multline}.
%    \begin{macrocode}
    \totwidth@\displaywidth %%*F
    \if@fleqn %%*F
        \advance\totwidth@-\@mathmargin %%*F
    \fi %%*F
    \halign\bgroup
        \Let@
        \let\tag\gobble@tag
        \hbox to\totwidth@{% %%*F
            \strut@$\m@th\displaystyle
%    \end{macrocode}
%    DMJ: In order to get the spacing of the last line right in fleqn
%    mode, we need to play a little game here.  Normally the
%    stretchability of the \cs{hskip} here will be suppressed by the
%    \cs{hfil} at the end of the template, except for the last line,
%    when that \cs{hfil} will be removed by the \cs{hfilneg} in
%    \lendmultline@.
%    \begin{macrocode}
            \if@fleqn %%*F
                \hskip 0pt plus 1000pt %%*F
            \else %%*F
                \hfil
            \fi %%*F
            {}##\hfil$%
        }%
        \crcr
%    \end{macrocode}
%    DMJ: In \opt{fleqn} mode, it's the \cs{tabskip} of
%    \cs{@mathmargin} that needs to be removed in the first line, not
%    the \cs{hfil} at the beginning of the template.
%    \begin{macrocode}
        \if@fleqn %%*F
            \hskip-\@mathmargin %%*F
        \else %%*F
            \hfilneg
        \fi %%*F
        \iftag@
            \ifdim\ltwidth@>\z@
                \box\mtagbox@
                \hskip\multlinetaggap@
            \else
                \rlap{%
                    \vbox{%
                        \normalbaselines
                        \hbox{\strut@\box\mtagbox@}%
                        \vbox to\mlineht@{}%
                    }%
                }%
%    \end{macrocode}
%    DMJ: This is just a whim of mine: if the equation tag doesn't fit
%    on the same line with the first line of the display, shouldn't
%    the first line be indented by \multlinegap?  This isn't backwards
%    compatible.
%    \begin{macrocode}
                \hskip\multlinegap %%*
            \fi
        \else
            \hskip\multlinegap
        \fi
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\rmultline@@}
%    \begin{macrocode}
\def\rmultline@@#1{%
    \rmmeasure@{#1}%
    \setbox\mtagbox@\hbox{%
        \iftag@
            \df@tag
        \else
            \if@eqnsw
                \global\tag@true
                \tagform@\theequation
            \fi
        \fi
    }%
    \dimen@\mwidth@
    \advance\dimen@\wd\mtagbox@
    \advance\dimen@\multlinetaggap@
    \if@fleqn %%*F
        \advance\dimen@\@mathmargin %%*F
    \fi %%*F
    \ifdim\dimen@>\displaywidth
        \rtwidth@\z@
    \else
        \rtwidth@\wd\mtagbox@
    \fi
    \rmultline@@@#1
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\rmultline@@@}
%    \begin{macrocode}
\def\rmultline@@@{%
    \displ@y
    \def\shoveright##1{%
        ##1%
        \hfilneg
        \iftag@
            \ifdim\rtwidth@>\z@
                \hskip\rtwidth@
                \hskip\multlinetaggap@
            \fi
        \else
            \hskip\multlinegap
        \fi
    }%
    \if@fleqn %%*F
        \def\shoveleft##1{##1}% %%*F
    \else %%*F
        \def\shoveleft##1{%
            \setboxz@h{$\m@th\displaystyle{}##1$}%
            \setbox\@ne\hbox{$\m@th\displaystyle##1$}%
            \hfilneg
            \hskip\multlinegap
            \hskip.5\wd\@ne
            \hskip-.5\wdz@
            ##1%
        }%
    \fi %%*F
    \if@fleqn %%*F
        \tabskip\@mathmargin %%*F
    \else %%*F
        \tabskip\z@skip %%*
    \fi %%*F
    \totwidth@\displaywidth %%*F
    \if@fleqn %%*F
        \advance\totwidth@-\@mathmargin %%*F
    \fi %%*F
    \halign\bgroup
        \Let@
        \let\tag\gobble@tag
        \hbox to\totwidth@{%
            \strut@$\m@th\displaystyle
            \if@fleqn %%*F
                \hskip 0pt plus 1000pt %%*F
            \else %%*F
                \hfil
            \fi %%*F
            {}##\hfil$%
        }%
        \crcr
        \if@fleqn %%*F
            \hskip-\@mathmargin %%*F
        \else %%*F
            \hfilneg
        \fi %%*F
        \hskip\multlinegap
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\endmultline}
% \begin{macro}{\endmultline*}
% We use some expandafters here to reduce the number
% of tokens in the replacement text of \verb;\endmultline;.
% \verb;\endmultline; and \verb;\endmultline*; are the same.
%    \begin{macrocode}
\def\endmultline{\iftagsleft@\expandafter\lendmultline@\else
  \expandafter\rendmultline@\fi\global\@ignoretrue}
%    \end{macrocode}
%    \begin{macrocode}
\expandafter\let\csname endmultline*\endcsname=\endmultline
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\lendmultline@}
%    \begin{macrocode}
\def\lendmultline@{\hfilneg\hskip\multlinegap\crcr\egroup$$}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\rendmultline@}
%    \begin{macrocode}
\def\rendmultline@{%
    \iftag@
        \ifdim\rtwidth@>\z@
            \hskip\multlinetaggap@
            \box\mtagbox@
        \else
%    \end{macrocode}
%    DMJ: More non-backwards compatible whim; see above.
%    \begin{macrocode}
            \hskip\multlinegap %%*
            \llap{%
                \vtop{%
                    \@movetag %%*T
                    \normalbaselines\null\hbox{\strut@\box\mtagbox@}%
                }%
            }%
        \fi
    \else
        \hskip\multlinegap
    \fi
    \hfilneg
    \crcr
    \egroup$$%
}
%    \end{macrocode}
% \end{macro}
%
%    \subsection{DMJ: Miscellaneous}
%
% \begin{macro}{\[}
%
%    DMJ: \cs\[ and \cs\] should be redefined for two reasons:
%
%    \begin{enumerate}
%
%    \item
%    so they act properly with \opt{fleqn} (of course, \fn{fleqn.clo}
%    will redefine them, so we have to be careful; see comments at
%    beginning of file)
%
%    \item
%    so the spacing above and below it is consistent with the other
%    \AMS-\LaTeX\ math environments when $\cs{abovedisplayskip} \ne
%    \cs{abovedisplayshortskip}$.
%
%    \end{enumerate}
%
%    For obvious reasons, this change is not backwards compatible.
%    [mjd,1994/10/11] Canceled change pending further tests. \verb
%    inside \[...\] would no longer work. That might be too big a
%    problem for existing documents.
%    \begin{macrocode}
%\def\[#1\]{\begin{equation*}#1\end{equation*}}
%    \end{macrocode}
% \end{macro}
%
% \subsection{Final incantations}
%
% \begin{macro}{\@arrayparboxrestore}
%    Here we must reset a few additional parameters.
%    In principle we also have to ensure that the \verb+\and@+
%    counter does not change over a \verb+\parbox+ or
%    {\tt minipage}.  But this can be done later.
%    \begin{macrocode}
\expandafter\def
 \expandafter\@arrayparboxrestore
  \expandafter{\@arrayparboxrestore
               \inany@false\ingather@false\inalign@false
   \default@tag}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\equation}
% \begin{macro}{\endequation}
%    The {\tt split} environment does not work inside a
%    {\tt displaymath} or {\tt equation} environment since it
%    must be enclosed by an alignment.
%    We therefore redefine the {\tt equation} environment to be
%    a one-lined {\tt gather} environment.
%    The \verb+\\+ command is made inaccessible in an {\tt equation}
%    environment.
%    \begin{macrocode}
\def\equation{\gather\def\\{\PackageError{amstex}{\Invalid@@\\}\@eha}}
\def\endequation{\endgather}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\equation*}
% \begin{macro}{\endequation*}
%    The {\tt equation*} environment is nearly the same; it only
%    suppresses the automatic generation of a tag.
%    \begin{macrocode}
\newenvironment{equation*}{%
  \equation
}{%
  \nonumber\endequation
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%    \begin{macrocode}
\newcounter{parentequation}% Counter for ``parent equation''.
%    \end{macrocode}
%
%    \begin{macrocode}
\newenvironment{subequations}[1]{%
%    \end{macrocode}
%    Before sending down the `equation' counter to the subordinate
%    level, add 1 using standard \refstepcounter.
%    \begin{macrocode}
  \refstepcounter{equation}%
%    \end{macrocode}
%    Define \cn{theparentequation} equivalent to current
%    \cn{theequation}. \cn{edef} is necessary to expand the current
%    value of the equation counter. This might in rare cases cause
%    something to blow up, in which case the user needs to add
%    \cn{protect}.
%    \begin{macrocode}
  \begingroup % conservative approach
  \let\protect\noexpand
  \edef\@tempa{\def\noexpand\theparentequation{\theequation}}%
  \expandafter\endgroup\@tempa
  \setcounter{parentequation}{\value{equation}}%
%    And set the equation counter to 0. It will be incremented to 1 (=
%    "a" or whatever) by \begin{xxx} where "xxx" is the name of an
%    equation environment such as `equation', `align', or `multline'
  \setcounter{equation}{0}%
  \toks@\ifx#11{\arabic}%
    \else\ifx#1i{\roman}\else\ifx#1I{\Roman}%
    \else\ifx#1A{\Alph}\else\ifx#1a{\alph}%
    \else\ifx#1f{\fnsymbol}%
    \else{}\fi\fi\fi\fi\fi\fi
  \edef\@tempa{\the\toks@}%
  \ifx\@tempa\@empty \@badnumtype{#1}\toks@{\alph}\fi
  \edef\theequation{\noexpand\theparentequation
    \the\toks@{equation}}%
  \ignorespaces
}{%
  \setcounter{equation}{\value{parentequation}}%
%    Prevent an extra space from creeping in after
%    \end{subequations}:
  \global\@ignoretrue
}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\@badnumtype#1{%
  \PackageError{amstex}{Unknown number type: `#1'}\@ehc}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \providecommand{\atchar}{{\normalfont\ttfamily\char64 }}
% \section{Handling of active {\atchar} character}
%
%     The \verb|@| character in [amstex] is used as a prefix
%     in various combinations including \verb|@,|, \verb|@!|,
%     and \verb|@>>>|. It is given category 13 (active) in
%     order to be able to select the right action based on
%     what follows. For consistency, we use a special macro
%     to define \verb|@| combinations. To give better looking error
%     messages if an error occurs in an |@| command, the internal name
%     consists of the command name as it appears to the user, with a
%     leading space added.
% \begin{macro}{\atdef@}
%    \begin{macrocode}
\def\atdef@#1{\expandafter\def\csname\space @\string#1\endcsname}
%    \end{macrocode}
% \end{macro}
%
%    We make the next definition inside a group because we don't want
%    \verb|@| to remain active for all following code, we only want it
%    activated the next time \LaTeX{} calls \cn{makeatother}.
%    \begin{macrocode}
\begingroup \catcode`\@=\active
\gdef @{\Iat}
\endgroup
\DeclareRobustCommand{\Iat}{\FN@\at@}
%    \end{macrocode}
%
%      \verb|\at@| gives an error message (\verb|\at@@@|) if the
%      following character---stored in \verb|\@let@token| by
%      \verb|\futurelet|---has an unusual catcode (not 11 or 12).
%      Otherwise it constructs a \verb|\csname| using that character
%      (actually it might be a control sequence, also, which will
%      be converted using \verb|\string|).
%    \begin{macrocode}
\def\at@{\let\next@\at@@
 \ifcat\noexpand\@let@token a\else
 \ifcat\noexpand\@let@token0\else
 \ifcat\noexpand\@let@token\relax\else
 \let\@let@token@\at@@@\fi\fi\fi\next@}
%    \end{macrocode}
%      If the category of the next token was OK, but this particular
%      combination was not defined, \verb|\at@@| calls \verb|\at@@@| to
%      give an error message. Otherwise we construct a suitable csname.
%    \begin{macrocode}
\def\at@@#1{\expandafter
  \@ifundefined{ @\string#1}%
    {\DN@{\at@@@#1}}%
    {\DN@{\csname\space @\string#1\endcsname}}%
  \next@}%
%    \end{macrocode}
%      If we encounter an invalid \verb|@| combination, we assume the
%      user wanted a real printed \verb|@| and so we typeset one, after
%      the error message.
%    \begin{macrocode}
\def\at@@@{\PackageError{amstex}{\Invalid@@ @}%
  {\the\athelp@}% "I'll assume you wanted @@"
  \char64\relax}
%    \end{macrocode}
%
%      This is the help message that goes along with the error message
%      of \verb|\at@@@|.
%    \begin{macrocode}
\newhelp\athelp@
{Only certain combinations beginning with @ make sense to me.^^J%
I'll assume you wanted @@ for a printed @.}
%    \end{macrocode}
%
%      If \verb|@| is active, we must have an alternative way for
%      printing the character in a document. It would be natural
%      to use \verb|\@| for this purpose but that is already taken
%      in \LaTeX{} for something else. So we resort to \verb|@@|.
%      We define \verb|@@| to expand to \verb|\atchar| (a \cn{chardef})
%      rather than a
%      category 12 or 11 \verb|@| character, so that it will be robust
%      if passed between files, e.g. to and from the .toc file. The
%      extra braces ensure that a following space is not lost if this
%      expansion gets passed to (e.g.) the toc file.
%    \begin{macrocode}
\atdef@ @{{\atchar}}% to define @@
\chardef\atchar=64
%    \end{macrocode}
%    And we must redefine \cs{makeatother} to set the category code of
%    \verb+@+ to active instead of other. Furthermore we must do some
%    surgery on \cs{@currnamestack} to make the catcode of \verb'@'
%    revert to active when \LaTeX{} once again reaches top level. We
%    can't just put \cs{makeatother} at the end of amstex.sty because
%    the \LaTeX{} package loading mechanisms will immediately override
%    with the previous value of \verb'@''s catcode. Not to mention that
%    the amstex package might be loaded inside a document class or
%    another package. When \LaTeX{} gets an interface for active
%    characters this can be fixed. :-)
%    \begin{macrocode}
\def\makeatother{\catcode64=\active}
\def\@tempa#1#2#3#4#5#6{%
  {#1}{#2}\ifnum0#6=0{13}\@xp\@gobblefour
  \else{#3}\fi\@tempa{#4}{#5}{#6}}%
\xdef\@currnamestack{\@xp\@tempa\@currnamestack{}{}{0}}
%    \end{macrocode}
%
% \begin{macro}{\@sanitize}
%    We have to add \verb+\@+ to the list of special characters
%    in \verb+\@sanitize+ otherwise \verb+\index+ and the like
%    will run amok.
%    \begin{macrocode}
{\def\@makeother{\noexpand\@makeother\noexpand}
\xdef\@sanitize{\@sanitize\@makeother\@}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\dospecials}
%    We have to add \verb+\@+ to the list of special characters
%    in \verb+\dospecials+ otherwise \verb+\verb+ or the verbatim
%    environments will run amok.
%    \begin{macrocode}
{\def\do{\noexpand\do\noexpand}
\xdef\dospecials{\dospecials\do\@}}
%    \end{macrocode}
% \end{macro}
%
%    The \verb+@.+ macro was moved to the {\tt amscd} style file.
%
%    The non-math alternatives in the following definitions are
%    superseded by \LaTeX's \verb+\@+ command and were therefore
%    removed.
%    \begin{macrocode}
\atdef@,{\ifmmode\mskip.1\thinmuskip\else \nonmatherr@{@,}\fi}
\atdef@!{\RIfM@\mskip-.1\thinmuskip\else \nonmatherr@{@!}\fi}
%    \end{macrocode}

%    The arrows \verb+@>>>+ and \verb+@<<<+ will be redefined by {\tt
%    amscd.sty} if that option is used.  These definitions here are
%    slightly reduced by removal of CD-specific code. Therefore we
%    must skip them if {\tt amscd} precedes {\tt amstex} in the
%    documentstyle options list.
%
%    Note that \verb|\rightarrowfill@| and \verb|\leftarrowfill@|
%    use smashed minus signs to prevent superscripts above the
%    arrows from being too high.
%    \begin{macrocode}
\@ifpackageloaded{amscd}{%
%    amscd loaded earlier: do nothing
}{%
%    amscd not loaded: OK to define @>>> and @<<<
\atdef@>#1>#2>{%
  \global\bigaw@\minaw@
  \setboxz@h{$\m@th\scriptstyle\;{#1}\;\;$}%
  \ifdim\wdz@>\bigaw@ \global\bigaw@\wdz@ \fi
%    \end{macrocode}
%    If \verb|#2| is empty we can save some work.
%    \begin{macrocode}
  \@ifnotempty{#2}{\setbox\@ne\hbox{$\m@th\scriptstyle\;{#2}\;\;$}%
    \ifdim\wd\@ne>\bigaw@ \global\bigaw@\wd\@ne \fi}%
   \mathrel{\mathop{\hbox to\bigaw@{\rightarrowfill@\displaystyle}}%
     \limits^{#1}\@ifnotempty{#2}{_{#2}}}%
}% end of @>>>
%
\atdef@<#1<#2<{%
  \global\bigaw@\minaw@
  \setboxz@h{$\m@th\scriptstyle\;\;{#1}\;$}%
  \ifdim\wdz@>\bigaw@ \global\bigaw@\wdz@ \fi
  \@ifnotempty{#2}{\setbox\@ne\hbox{$\m@th\scriptstyle\;\;{#2}\;$}%
    \ifdim\wd\@ne>\bigaw@ \global\bigaw@\wd\@ne \fi}%
  \mathrel{\mathop{\hbox to\bigaw@{\leftarrowfill@\displaystyle}}%
      \limits^{#1}\@ifnotempty{#2}{_{#2}}}%
}% end of @<<<
}% end of @ifpackageloaded
%    \end{macrocode}
%
%    We use \verb|\@ifundefined| tests here for \verb|\minaw@| and
%    \verb|\bigaw@| so that they will not be reallocated if {\tt
%    amscd} precedes {\tt amstex} in a documentstyle options list.
%    \begin{macrocode}
\@ifundefined{minaw@}{\newdimen\minaw@}{}
\minaw@11.111pt
\@ifundefined{bigaw@}{\newdimen\bigaw@}{}
%    \end{macrocode}
%
%    Non-breaking hyphen command of amstex.
%    Setting the hyphen in a box and then unboxing it means that the
%    normal penalty will not be added after it---and if the penalty is
%    not there a break will not be taken (unless an explicit penalty
%    or glue follows, thus the final \cw{nobreak}). To begin the
%    recursion we make \cw{next} = hyphen; after that \cw{next}
%    will be equal or not equal to hyphen depending on the result of
%    the \cw{futurelet} in \cw{FN@}.
%    \begin{macrocode}
\atdef@-{\let\next-%%
  \DN@{\ifx\next-%%
    \def\next-{\setbox\z@\hbox{-}\unhbox\z@\FN@\next@}%%
    \expandafter\next \else\nobreak\fi}%%
  \next@-}%%
%    \end{macrocode}
%
%    This root stuff needs syntax work and implementation work. Surely
%    something more compact can be done?? [mjd,5-Sep-1994]
%    \begin{macrocode}
\def\leftroot{\PackageError{amstex}{\Invalid@@\leftroot}\@eha}
\def\uproot{\PackageError{amstex}{\Invalid@@\uproot}\@eha}
\newcount\uproot@
\newcount\leftroot@
\def\root{\relaxnext@
  \DN@{\ifx\@let@token\uproot\let\next@\nextii@\else
   \ifx\@let@token\leftroot\let\next@\nextiii@\else
   \let\next@\plainroot@\fi\fi\next@}%
  \def\nextii@\uproot##1{\uproot@##1\relax\FN@\nextiv@}%
  \def\nextiv@{\ifx\@let@token\@sptoken\DN@. {\FN@\nextv@}\else
   \DN@.{\FN@\nextv@}\fi\next@.}%
  \def\nextv@{\ifx\@let@token\leftroot\let\next@\nextvi@\else
   \let\next@\plainroot@\fi\next@}%
  \def\nextvi@\leftroot##1{\leftroot@##1\relax\plainroot@}%
   \def\nextiii@\leftroot##1{\leftroot@##1\relax\FN@\nextvii@}%
  \def\nextvii@{\ifx\@let@token\@sptoken
   \DN@. {\FN@\nextviii@}\else
   \DN@.{\FN@\nextviii@}\fi\next@.}%
  \def\nextviii@{\ifx\@let@token\uproot\let\next@\nextix@\else
   \let\next@\plainroot@\fi\next@}%
  \def\nextix@\uproot##1{\uproot@##1\relax\plainroot@}%
  \bgroup\uproot@\z@\leftroot@\z@\FN@\next@}
\def\plainroot@#1\of#2{\setbox\rootbox\hbox{%
 $\m@th\scriptscriptstyle{#1}$}%
 \mathchoice{\r@@t\displaystyle{#2}}{\r@@t\textstyle{#2}}
 {\r@@t\scriptstyle{#2}}{\r@@t\scriptscriptstyle{#2}}\egroup}
\def\r@@t#1#2{\setboxz@h{$\m@th#1\@@sqrt{#2}$}%
 \dimen@\ht\z@\advance\dimen@-\dp\z@
 \setbox\@ne\hbox{$\m@th#1\mskip\uproot@ mu$}%
 \advance\dimen@ by1.667\wd\@ne
 \mkern-\leftroot@ mu\mkern5mu\raise.6\dimen@\copy\rootbox
 \mkern-10mu\mkern\leftroot@ mu\boxz@}
%    \end{macrocode}
%
%    The usual \cs{endinput} to ensure that random garbage at the end of
%    the file doesn't get copied by \fn{docstrip}.
%    \begin{macrocode}
\endinput
%    \end{macrocode}
%
% \CheckSum{3777}
% \Finale