% some simple math constructs

\unprotect

\def\numberedeqalign
  {\doifelse\@@fmlocation\v!left\leqalignno\eqalignno}

\def\doalignNR[#1][#2]%
  {\doifsomething{#1}
     {\doifelse{#1}{+}
        {\doformulanumber[][#2][]{}}
        {\doformulanumber[#1][#2][]{}}}}

\long\def\startalign#1\stopalign
  {\def\NC{\crcr\def\NC####1{&####1}}%
   \def\EQ{&=}
   \def\NR{&\dodoubleempty\doalignNR}%
   % amstex compatibility mode:
   \def\notag{\def\\{&\crcr}}%
   \def\\{&\doalignNR[+][]\crcr}%
   % end of compatibility mode
   \numberedeqalign{#1\relax}}

%D \startbuffer
%D \placeformula \startformula \eqalignno {
%D  a &= b & \formulanumber \cr
%D  c &= d \cr
%D    &= e \cr
%D    &= f & \formulanumber
%D } \stopformula
%D \stopbuffer
%D
%D \typebuffer \getbuffer
%D
%D \startbuffer
%D \placeformula \startformula \startalign
%D \NC  a \EQ b \NR[+]
%D \NC  c \EQ d \NR
%D \NC    \EQ f \NR[for:hans]
%D \NC    \EQ g \NR[for:whoelse][a]
%D \NC    \EQ h \NR[for:whomore][b]
%D \NC    \EQ i \NR
%D \stopalign \stopformula
%D \stopbuffer
%D
%D \typebuffer \getbuffer
%D
%D \startbuffer
%D \placeformula \startformula \startalign
%D \NC a \EQ b \NR[+]
%D \NC c \EQ d \NR
%D \NC   \EQ f \NR
%D \NC   \EQ g \NR
%D \NC   \EQ h \NR
%D \NC   \EQ i \NR[+]
%D \stopalign \stopformula
%D \stopbuffer
%D
%D \typebuffer \getbuffer
%D
%D \startbuffer
%D \placeformula \startformula \startalign
%D a &= b \\
%D c &= d \notag \\
%D   &= e \notag \\
%D   &= f \\
%D \stopalign \stopformula
%D \stopbuffer
%D
%D \typebuffer \getbuffer
%D
%D \startbuffer
%D \placeformula \startformula \startalign
%D a &= b \NR[+]
%D c &= d \NR
%D   &= e \NR
%D   &= f \NR[+]
%D \stopalign \stopformula
%D \stopbuffer
%D
%D \typebuffer \getbuffer
%D
%D \startbuffer
%D \placeformula \startformula \startalign
%D \NC  a \NC \eq  b \NR[+]
%D \NC  c \NC \neq d \NR
%D \NC    \NC \neq f \NR[for:hans]
%D \NC    \NC \geq g \NR[for:whoelse][a]
%D \NC    \NC \leq h \NR[for:whomore][b]
%D \NC    \NC \neq i \NR
%D \stopalign \stopformula
%D \stopbuffer
%D
%D \typebuffer \getbuffer

\protect \endinput