This bug was discovered by Kostas Oikonomou, who uses
the TeXmacs interface. But it is really a bug in
tex-mexpt. Just do this:
:lisp (tex '((mexpt) $a ((mminus) ((mplus) $b $c)))
nil nil 'mparen 'mparen)
and you get
(A ^ {- B + C })
The sum B+C is not in parenthes, though it should be.
To fix this bug, a simple change in mactex.lisp is
sufficient. In the function tex-mexpt, replace the line
(tex (cadr x) '("^ {- ")(cons " }" r) 'mparen 'mparen))
by the line
(tex (cadr x) '("^ {- ")(cons " }" r) 'mminus 'mparen))
Andrey