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Chapter 59
Other

   59.1 Springer Lecture Notes

The \label gets a definition that differs a little than the one in LaTeX, and is more complicated because of cases like in the example:

\documentclass[fleqn]{article} 
 
\title{Test of subequations environment} 
\author{mjd} 
 
\usepackage[noamsfonts]{amstex} 
\numberwithin{equation}{section} 
 
\newcommand{\env}[1]{{\normalfont\texttt{#1}}} 
 
 
   \begin{document} 
 
‘\section{Prime equation numbers} 
 
 
Here is a,b,c sub-numbering. 
\begin{subequations}{a} 
\begin{eqnarray} 
A&=&B\\ 
D&=&C \label{e:middle}\\ 
E&=&F 
\end{eqnarray} 
\end{subequations} 
That was produced with the \env{eqnarray} environment; the middle line 
was labeled as \eqref{e:middle}. 
 
 
 
First an equation. 
\begin{equation}\label{e:previous} 
A=B 
\end{equation} 
That was equation \eqref{e:previous}. 
 
 
\begin{equation}% 
\tag{\ref{e:previous}$’$} 
\label{e:prevprime} 
C=D 
\end{equation} 
 
 And that was equation \eqref{e:prevprime}. 
 
 
 
First an equation. 
\begin{subequations}{a} 
\begin{xalignat}{2} 
\label{xalignat:a}A+B&=B&     B&=B+A\\ 
\label{xalignat:b}C&=D+E&     C\oplus D&=E\\ 
\label{xalignat:c}E&=F&       E’&=F’ 
\end{xalignat} 
\end{subequations} 
 
Label check: that was \eqref{xalignat:a}, \eqref{xalignat:b}, and 
\eqref{xalignat:c}. 
 
\end{document} 

Note that the above fails if \@currentlabel has a ‘\Link[]...’.

<..equations of amstex.sty..>
 \append:defI\subequations{\cur:lbl{}\let\cur:lbl=\:gobble \ignorespaces}
 -_-_-

With the exception of \subequations, the \refstepcounter of LaTeX is not used. The following is to compensate for the lost \Link.

<..equations of amstex.sty..>+
 \let\:stepcounter=\stepcounter
 \append:defI\stepcounter{%
    \ifx \EndPicture\:UnDef\else \def\:temp{equation}\def\:tempa{#1}%
    \ifx\:temp\:tempa
       \edef\:currentlabel{E\the\c@equation}\let\cur:lbl=\:gobble
       \edef\cur:th{<.haddr prefix.>\last:haddr}%
       \edef\:temp{\noexpand\AfterPicture{\noexpand\a:eqno\noexpand
          \Make:Label{\cur:th \:currentlabel}{}%
          \noexpand\html:addr}}\:temp
       \let\stepcounter=\:stepcounter
    \fi\fi }
 -_-_-

<..haddr prefix..>
 x-_-_-

<..equations of amstex.sty..>+
 \let\:insplit=\insplit@
 \def\insplit@{\let\halign=\TeXhalign \:insplit}
 -_-_-

Place the number with the equation; not under.

<..equations of amstex.sty..>+
 \NewConfigure{eqn}[1]{\def\a:eqno{#1}}
 -_-_-

<..equations of amstex.sty..>+
 \pend:def\gather{\a:gather}
 \append:def\endgather{\b:gather}
 \@xp\pend:def\csname gather*\endcsname{\Picture*{}}
 \@xp\append:def\csname endgather*\endcsname{\EndPicture}
 \NewConfigure{gather}{2}
 -_-_-

In amslatex.sty, equation is defined in terms of gather.

<..equations of amstex.sty..>+
 \pend:def\equation{\bgroup \let\tagform@=\:gobble}
 \append:def\endequation{\egroup}
 -_-_-

<..equations of amstex.sty..>+
 \pend:def\align{\Picture*{}}
 \append:def\endalign{\EndPicture}
 \@xp\pend:def\csname align*\endcsname{\Picture*{}}
 \@xp\append:def\csname endalign*\endcsname{\EndPicture}
 -_-_-

<..equations of amstex.sty..>+
 \pend:defI\alignat{\Picture*{}}
 \append:def\endalignat{\EndPicture}
 \expandafter\pend:defI\csname alignat*\endcsname{\Picture*{}}
 \expandafter\append:def\csname endalignat*\endcsname{\EndPicture}
 -_-_-

<..equations of amstex.sty..>+
 \pend:defI\xalignat{\Picture*{}}
 \append:def\endxalignat{\EndPicture}
 \expandafter\pend:defI\csname xalignat*\endcsname{\Picture*{}}
 \expandafter\append:def\csname endxalignat*\endcsname{\EndPicture}
 -_-_-

<..equations of amstex.sty..>+
 \pend:defI\xxalignat{\Picture*{}}
 \append:def\endxxalignat{\EndPicture}
 -_-_-

<..equations of amstex.sty..>+
 \pend:def\alignedat{\Picture*{}$}
 \append:def\endalignedat{$\EndPicture}
 -_-_-

<..equations of amstex.sty..>+
 \pend:def\gathered{\Picture*{}$}
 \append:def\endgathered{$\EndPicture}
 -_-_-

<..equations of amstex.sty..>+
 \pend:def\multline{\Picture*{}}
 \append:def\endmultline{\EndPicture}
 \expandafter\pend:def\csname multline*\endcsname{\Picture*{}}
 \expandafter\append:def\csname endmultline*\endcsname{\EndPicture}
 -_-_-

<..equations of amstex.sty..>+
 \let\:smallmatrix=\smallmatrix
 \def\smallmatrix{\Picture*{}$\:smallmatrix}
 \append:def\endsmallmatrix{$\EndPicture}
 -_-_-

<..body of amstex.sty..>
 <.amsmath.sty and amstex.sty.>
 -_-_-

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