(VAR x y xs fun)
(RULES
  app(app(minus, x), 0) -> x
  app(app(minus, app(s, x)), app(s, y)) -> app(app(minus, x), y)
  app(f, 0) -> app(s, 0)
  app(f, app(s, x)) -> app(app(minus, app(s, x)), app(g, app(f, x)))
  app(g, 0) -> 0
  app(g, app(s, x)) -> app(app(minus, app(s, x)), app(f, app(g, x)))

  app(app(map,fun),nil) -> nil
  app(app(map,fun),app(app(cons,x),xs)) -> app(app(cons,app(fun,x)),app(app(map,fun),xs))

  app(app(filter,fun),nil) -> nil
  app(app(filter,fun),app(app(cons,x),xs)) -> app(app(app(app(filter2,app(fun, x)),fun),x),xs)
  app(app(app(app(filter2,true),fun),x),xs) -> app(app(cons,x),app(app(filter,fun),xs))
  app(app(app(app(filter2,false),fun),x),xs) -> app(app(filter,fun),xs)

)