execute (IVal s1 : IVal s2 : ss) (Mul     : xs) = execute (s'     : ss) xs where s' = IVal (s1 * s2)
execute (IVal s1 : IVal s2 : ss) (Mul     : xs) = execute (s'     : ss) xs where s' = IVal (s1 * s2)
execute (IVal s1 : IVal s2 : ss) (Mul     : xs) = execute (s'     : ss) xs where s' = IVal (s1 * s2)