(VAR f x xs y ys )
(RULES 
        ap(ap(map, f), xs) -> ap(ap(ap(if, ap(isEmpty, xs)), f), xs)
        ap(ap(ap(if, true), f), xs) -> null
        ap(ap(ap(if, null), f), xs) -> ap(ap(cons, ap(f, ap(last, xs))), ap(ap(if2, f), xs))
        ap(ap(if2, f), xs) -> ap(ap(map, f), ap(dropLast, xs))
        ap(isEmpty, null) -> true
        ap(isEmpty, ap(ap(cons, x), xs)) -> null
        ap(last, ap(ap(cons, x), null)) -> x
        ap(last, ap(ap(cons, x), ap(ap(cons, y), ys))) -> ap(last, ap(ap(cons, y), ys))
        ap(dropLast, ap(ap(cons, x), null)) -> null
        ap(dropLast, ap(ap(cons, x), ap(ap(cons, y), ys))) -> ap(ap(cons, x), ap(dropLast, ap(ap(cons, y), ys)))
        
)