You need to be careful with \cases and quite a few other similar items. If you
look at how \begin and \end work, \begin{foo} is equivilent to \foo and
\end{foo} to \endfoo. If you do not load the appropiate ams style file then you
get the plain TeX version of \cases (a macro based on a halign, seperate cases
with \cr).
Once you load the amslatex style the detials of the macro change and leaving
out the \endcases (aka \end{cases} becomes a sin publishable by grouping
problems. The same can be said for \eqalign and many other plain TeX
constructs. Things like \bordermatrix are likely to be particularly itirating,
which is not exactly simple (it uses unboxing and several boxes).
I think \atop, \over, \above, \atopwithdelims, etc are all unaffected by this
particular problem. The ams enhancement to \frac essential corresponds to
replacing \over with \above.
--
Duncan (-:
"software industry, the: unique industry where selling substandard goods is
legal and you can charge extra for fixing the problems."
