MAYBE
Trs:
 {                             app(len(), nil()) -> 0(),
             app(len(), app(app(cons(), x), xs)) -> app(s(), app(len(), xs)),
       app(app(sub(), app(s(), x)), app(s(), y)) -> app(app(sub(), x), y),
                         app(app(sub(), x), 0()) -> x,
         app(app(d(), app(s(), x)), app(s(), y)) -> app(app(app(if(), app(app(gtr(), x), y)), false()), app(app(d(), app(s(), x)), app(app(sub(), y), x))),
                           app(app(d(), x), 0()) -> true(),
                         app(app(gtr(), 0()), y) -> false(),
               app(app(gtr(), app(s(), x)), 0()) -> true(),
       app(app(gtr(), app(s(), x)), app(s(), y)) -> app(app(gtr(), x), y),
                    app(app(filter(), p), nil()) -> nil(),
  app(app(filter(), p), app(app(cons(), x), xs)) -> app(app(app(if(), app(p, x)), app(app(cons(), x), app(app(filter(), p), xs))), app(app(filter(), p), xs)),
             app(app(app(if(), true()), xs), ys) -> xs,
            app(app(app(if(), false()), xs), ys) -> ys}
 Comment:
  We consider a duplicating trs.
  FAIL:
   Open