Conversion to perform addition on two integer literals of type :int.
The call INT_MAX_CONV `max c1 c2` where c1 and c2 are integer literals
of type :int, returns |- max c1 c2 = d where d is the canonical integer
literal that is equal to max c1 c2. The literals c1 and c2 may be of the
form &n or -- &n (with nonzero n in the latter case) and the result will
be of the same form.
Fails if applied to a term that is not the maximum operator applied to two
permitted integer literals of type :int.
# INT_MAX_CONV `max (-- &1) (&2)`;;
val it : thm = |- max (-- &1) (&2) = &2