(VAR f x xs y )
(RULES 
        app(p, app(s, x)) -> x
        app(fact, 0) -> app(s, 0)
        app(fact, app(s, x)) -> app(app(*, app(s, x)), app(fact, app(p, app(s, x))))
        app(app(*, 0), y) -> 0
        app(app(*, app(s, x)), y) -> app(app(+, app(app(*, x), y)), y)
        app(app(+, x), 0) -> x
        app(app(+, x), app(s, y)) -> app(s, app(app(+, x), y))
        app(app(map, f), nil) -> nil
        app(app(map, f), app(app(cons, x), xs)) -> app(app(cons, app(f, x)), app(app(map, f), xs))
        app(app(filter, f), nil) -> nil
        app(app(filter, f), app(app(cons, x), xs)) -> app(app(app(app(filter2, app(f, x)), f), x), xs)
        app(app(app(app(filter2, true), f), x), xs) -> app(app(cons, x), app(app(filter, f), xs))
        app(app(app(app(filter2, false), f), x), xs) -> app(app(filter, f), xs)
        
)