Here's a quick example of an AmSTeX file including a Cyrillic symbol.
\documentstyle{amsppt}
\font\tencyr=wncyr10 % scaled \magstep1
\font\sevencyr=wncyr7 % scaled \magstep1
\font\fivecyr=wncyr5 % scaled \magstep1
\newfam\cyrfam \textfont\cyrfam=\tencyr \scriptfont\cyrfam=\sevencyr
\scriptscriptfont\cyrfam=\fivecyr
\define\hexfam#1{\ifcase\number#1
0\or 1\or 2\or 3\or 4\or 5\or 6\or 7 \or
8\or 9\or A\or B\or C\or D\or E\or F\fi}
\mathchardef\Sha="0\hexfam\cyrfam 58
\document
This is the Tate-Shafarevich group: $\Sha_{E/K}$.
Here it is as a subscript: $A_\Sha$.
\enddocument
Last updated 16 March 2005