(VAR fun x xs y )
(RULES 
        app(app(minus, x), 0) -> x
        app(app(minus, app(s, x)), app(s, y)) -> app(app(minus, x), y)
        app(f, 0) -> app(s, 0)
        app(f, app(s, x)) -> app(app(minus, app(s, x)), app(g, app(f, x)))
        app(g, 0) -> 0
        app(g, app(s, x)) -> app(app(minus, app(s, x)), app(f, app(g, x)))
        app(app(map, fun), nil) -> nil
        app(app(map, fun), app(app(cons, x), xs)) -> app(app(cons, app(fun, x)), app(app(map, fun), xs))
        app(app(filter, fun), nil) -> nil
        app(app(filter, fun), app(app(cons, x), xs)) -> app(app(app(app(filter2, app(fun, x)), fun), x), xs)
        app(app(app(app(filter2, true), fun), x), xs) -> app(app(cons, x), app(app(filter, fun), xs))
        app(app(app(app(filter2, false), fun), x), xs) -> app(app(filter, fun), xs)
        
)