MAYBE
Trs:
 {                  app(app(filter(), f), nil()) -> nil(),
  app(app(filter(), f), app(app(cons(), x), xs)) -> app(app(app(consif(), app(f, x)), x), app(app(filter(), f), xs)),
          app(app(app(consif(), true()), x), ys) -> app(app(cons(), x), ys),
         app(app(app(consif(), false()), x), ys) -> ys}
 Comment:
  We consider a duplicating trs.
  FAIL:
   Open