MAYBE
MAYBE
TRS:
 {
               app(app(app(if(), true()), x), y) -> x,
              app(app(app(if(), false()), x), y) -> y,
  app(app(filter(), f), app(app(cons(), x), xs)) ->
  app(
     app(app(if(), app(f, x)), app(app(cons(), x), app(app(filter(), f), xs))
     ), app(app(filter(), f), xs)
  ),
                    app(app(filter(), f), nil()) -> nil()
 }
 DUP: We consider a duplicating system.
  Trs:
   {
                 app(app(app(if(), true()), x), y) -> x,
                app(app(app(if(), false()), x), y) -> y,
    app(app(filter(), f), app(app(cons(), x), xs)) ->
    app(
       app(
          app(if(), app(f, x)),
          app(app(cons(), x), app(app(filter(), f), xs))
       ), app(app(filter(), f), xs)
    ),
                      app(app(filter(), f), nil()) -> nil()
   }
  Fail