(VAR y x f) (RULES app(app(add, 0), y) -> y app(app(add, app(s, x)), y) -> app(s, app(app(add, x), y)) app(app(mult, 0), y) -> 0 app(app(mult, app(s, x)), y) -> app(app(add, app(app(mult, x), y)), y) app(app(app(rec, f), x), 0) -> x app(app(app(rec, f), x), app(s, y)) -> app(app(f, app(s, y)), app(app(app(rec, f), x), y)) fact -> app(app(rec, mult), app(s, 0)) )