MAYBE
MAYBE
TRS:
 {
                                              app(app(map(), f), nil()) ->
  nil(),
                            app(app(map(), f), app(app(cons(), x), xs)) ->
  app(app(cons(), app(f, x)), app(app(map(), f), xs)),
                                          app(app(append(), xs), nil()) -> xs,
                                          app(app(append(), nil()), ys) -> ys,
                        app(app(append(), app(app(cons(), x), xs)), ys) ->
  app(app(cons(), x), app(app(append(), xs), ys)),
                                            app(app(zip(), xss), nil()) ->
  xss,
                                            app(app(zip(), nil()), yss) ->
  yss,
  app(app(zip(), app(app(cons(), xs), xss)), app(app(cons(), ys), yss)) ->
  app(app(cons(), app(app(append(), xs), ys)), app(app(zip(), xss), yss)),
                                         app(app(combine(), xs), nil()) -> xs,
                     app(app(combine(), xs), app(app(cons(), ys), yss)) ->
  app(app(combine(), app(app(zip(), xs), ys)), yss),
                                 app(levels(), app(app(node(), x), xs)) ->
  app(
     app(cons(), app(app(cons(), x), nil())),
     app(app(combine(), nil()), app(app(map(), levels()), xs))
  )
 }
 DUP: We consider a duplicating system.
  Trs:
   {
                                                app(app(map(), f), nil()) ->
    nil(),
                              app(app(map(), f), app(app(cons(), x), xs)) ->
    app(app(cons(), app(f, x)), app(app(map(), f), xs)),
                                            app(app(append(), xs), nil()) ->
    xs,
                                            app(app(append(), nil()), ys) ->
    ys,
                          app(app(append(), app(app(cons(), x), xs)), ys) ->
    app(app(cons(), x), app(app(append(), xs), ys)),
                                              app(app(zip(), xss), nil()) ->
    xss,
                                              app(app(zip(), nil()), yss) ->
    yss,
    app(app(zip(), app(app(cons(), xs), xss)), app(app(cons(), ys), yss)) ->
    app(app(cons(), app(app(append(), xs), ys)), app(app(zip(), xss), yss)),
                                           app(app(combine(), xs), nil()) ->
    xs,
                       app(app(combine(), xs), app(app(cons(), ys), yss)) ->
    app(app(combine(), app(app(zip(), xs), ys)), yss),
                                   app(levels(), app(app(node(), x), xs)) ->
    app(
       app(cons(), app(app(cons(), x), nil())),
       app(app(combine(), nil()), app(app(map(), levels()), xs))
    )
   }
  Fail