(VAR f x xs y)
(RULES
  app(app(map, f), nil) -> nil
  app(app(map, f), app(app(cons, x), xs)) -> app(app(cons, app(f, x)), app(app(map, f), xs))
  app(sum, app(app(cons, x), xs)) -> app(app(plus, x), app(sum, xs))
  app(size, app(app(node, x), xs)) -> app(s, app(sum, app(app(map, size), xs)))
  app(app(plus, 0), x) -> 0
  app(app(plus, app(s, x)), y) -> app(s, app(app(plus, x), y))
)