60.2 Sub/Sub scripts

<..body of amstex.tex..>+
 \def\Sb#1\endSb{\sb{\a:multilimits
    \multilimits@#1\endSb\b:multilimits}}
 \def\Sp#1\endSp{\sp{\a:multilimits
    \multilimits@#1\endSp\b:multilimits}}
 \def\multilimits@{\bgroup\vspace@\Let@
  \baselineskip\fontdimen10 \scriptfont\tw@
  \advance\baselineskip\fontdimen12 \scriptfont\tw@
  \lineskip\thr@@\fontdimen8 \scriptfont\thr@@
  \lineskiplimit\lineskip  \let\halign=\TeXhalign
  \vbox\bgroup\ialign\bgroup\hfil\c:multilimits
     $\m@th\scriptstyle{##}$\d:multilimits\hfil\crcr}
 \NewConfigure{multilimits}{4}
 -_-_-