mul2* is the two-argument non-simplifying symbolic
multiplication function (defined in opers.lisp).
I think it is incorrect that if its args are numbers, it uses
fixnum multiplication (f*) rather than general
multiplication (*), though I can't find any cases where it
All the other XXX, XXX*, XXX2 and XXX2* operations in
opers use general Lisp arithmetic, not fixnum.