In core-mat.tex \frac is defined as
\def\dofrac#1#2#3{\relax\mathematics{{{#1{#2}}\over{#1{#3}}}}}
\unexpanded\def\frac
{\dofrac\mathstyle}
Shouldn't that be
\def\dofrac#1#2#3{\relax\mathematics{{\begingroup#1{#2}\endgroup\over#1{#3}}}}
Basically, \begingroup ... endgroup instead of bgroup ... egroup
generated by the braces. Compare the definition of \frac in core-mat
with the definition of genfrac in m-newmat. I am not sure whether this
really creates a difference or not, but generally most math definition
try to avoid creating an extra group. Even LaTeX defines \frac as
\def\frac#1#2{{\begingroup#1\endgroup\over#2}}
So, should the definition of \dofrac be changed?
Aditya