Conversion to prove whether one integer literal of type :int is <=
The call INT_LE_CONV `c1 <= c2` where c1 and c2 are integer
literals of type :int, returns whichever of |- c1 <= c2 <=> T or
|- c1 <= c2 <=> F is true. By an integer literal we mean either &n or
-- &n where n is a numeral.
Fails if applied to a term that is not the appropriate inequality comparison on
two permitted integer literals of type :int.
# INT_LE_CONV `&11 <= &77`;;
val it : thm = |- &11 <= &77 <=> T