(VAR f x xs y )
(RULES 
        app(app(le, 0), y) -> true
        app(app(le, app(s, x)), 0) -> false
        app(app(le, app(s, x)), app(s, y)) -> app(app(le, x), y)
        app(pred, app(s, x)) -> x
        app(app(minus, x), 0) -> x
        app(app(minus, x), app(s, y)) -> app(pred, app(app(minus, x), y))
        app(app(gcd, 0), y) -> y
        app(app(gcd, app(s, x)), 0) -> app(s, x)
        app(app(gcd, app(s, x)), app(s, y)) -> app(app(app(if_gcd, app(app(le, y), x)), app(s, x)), app(s, y))
        app(app(app(if_gcd, true), app(s, x)), app(s, y)) -> app(app(gcd, app(app(minus, x), y)), app(s, y))
        app(app(app(if_gcd, false), app(s, x)), app(s, y)) -> app(app(gcd, app(app(minus, y), x)), app(s, x))
        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)
        
)