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