(VAR f x y z ) (RULES app(app(app(fold, f), x), nil) -> x app(app(app(fold, f), x), app(app(cons, y), z)) -> app(app(f, y), app(app(app(fold, f), x), z)) app(app(plus, 0), y) -> y app(app(plus, app(s, x)), y) -> app(s, app(app(plus, x), y)) app(app(times, 0), y) -> 0 app(app(times, app(s, x)), y) -> app(app(plus, app(app(times, x), y)), y) sum -> app(app(fold, add), 0) prod -> app(app(fold, mul), app(s, 0)) )