(VAR x y z xs fun)
(RULES
  app(app(app(f, 0), 1), x) -> app(app(app(f, app(s, x)), x), x)
  app(app(app(f, x), y), app(s, z)) -> app(s, app(app(app(f, 0), 1), z))

  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)
)