(VAR y z x) (RULES app(f, app(app(cons, nil), y)) -> y app(f, app(app(cons, app(f, app(app(cons, nil), y))), z)) -> app(app(app(copy, n), y), z) app(app(app(copy, 0), y), z) -> app(f, z) app(app(app(copy, app(s, x)), y), z) -> app(app(app(copy, x), y), app(app(cons, app(f, y)), z)) )