subeqn.sty

%
% This LaTeX environment is for printing subequations.   
% To use this environment, include in the \documentstyle 
% header a command to load in the .sty file containing this macro.
%
% Example:
%
%   \documentstyle[11pt,subeqn]{article}
%
%   \begin{subequations}
%   \begin{eqnarray}
%   & & [equation] \label{1.1a} \\
%   & & [equation] \label{1.1b}
%   \end{eqnarray}
%   \label{1.1}
%   \end{subequations}
%
%   You can then refer to either 1.1, 1.1a, or 1.1b.
%
% Modified : June 8, 1989.  You can now reference either individual
%            equations in the subequations environment, or all of
%            them.  If you use a \label command immediately after the
%            \begin{subequations} command, then a reference to that
%            label will generate a reference to the equation number
%            without the alphabetic extension.
%
% Modified : 16 - january - 1989 by Johannes Braams ( BRAAMS@HLSDNL5)
%            Added \global\@ignoretrue in the definition of
%            \endsubequations in order to prevent a spurious space
%            at the beginning of the next text-line. Also added %'s
%            at the end of each command-line for the same reasons.
%
%%%----------------------------------------------------------------
%%% File: subeqn.sty
%%% The subequations environment %%%
%
% Within the subequations environment, the only change is that
% equations are labeled differently.  The number stays the same,
% and lower case letters are appended.  For example, if after doing
% three equations, numbered 1, 2, and 3, you start a subequations
% environmment and do three more equations, they will be numbered
% 4a, 4b, and 4c.  After you end the subequations environment, the
% next equation will be numbered 5.
%
% Both text and equations can be put inside the subequations 
% environment.
% If you make any improvements, I'd like to hear about them.
%
%
\newtoks\@stequation

\def\subequations{\refstepcounter{equation}%
  \edef\@savedequation{\the\c@equation}%
  \@stequation=\expandafter{\theequation}%   %only want \theequation
  \edef\@savedtheequation{\the\@stequation}% %expanded once
  \edef\oldtheequation{\theequation}%
  \setcounter{equation}{0}%
  \def\theequation{\oldtheequation\alph{equation}}}%

\def\endsubequations{%
  \setcounter{equation}{\@savedequation}%
  \@stequation=\expandafter{\@savedtheequation}%
  \edef\theequation{\the\@stequation}\global\@ignoretrue}
%%%----------------------------