(VAR x 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)) )