MAYBE
MAYBE
TRS:
 {
                  __(X1, mark(X2)) -> mark(__(X1, X2)),
                  __(mark(X1), X2) -> mark(__(X1, X2)),
                __(ok(X1), ok(X2)) -> ok(__(X1, X2)),
              active(__(X, nil())) -> mark(X),
                active(__(X1, X2)) -> __(X1, active(X2)),
                active(__(X1, X2)) -> __(active(X1), X2),
           active(__(__(X, Y), Z)) -> mark(__(X, __(Y, Z))),
              active(__(nil(), X)) -> mark(X),
                    active(U12(X)) -> U12(active(X)),
                 active(U12(tt())) -> mark(tt()),
                    active(U11(X)) -> U11(active(X)),
                 active(U11(tt())) -> mark(U12(tt())),
                active(isNePal(X)) -> isNePal(active(X)),
  active(isNePal(__(I, __(P, I)))) -> mark(U11(tt())),
                      U12(mark(X)) -> mark(U12(X)),
                        U12(ok(X)) -> ok(U12(X)),
                      U11(mark(X)) -> mark(U11(X)),
                        U11(ok(X)) -> ok(U11(X)),
                  isNePal(mark(X)) -> mark(isNePal(X)),
                    isNePal(ok(X)) -> ok(isNePal(X)),
                proper(__(X1, X2)) -> __(proper(X1), proper(X2)),
                     proper(nil()) -> ok(nil()),
                    proper(U12(X)) -> U12(proper(X)),
                      proper(tt()) -> ok(tt()),
                    proper(U11(X)) -> U11(proper(X)),
                proper(isNePal(X)) -> isNePal(proper(X)),
                      top(mark(X)) -> top(proper(X)),
                        top(ok(X)) -> top(active(X))
 }
 DUP: We consider a non-duplicating system.
  Trs:
   {
                    __(X1, mark(X2)) -> mark(__(X1, X2)),
                    __(mark(X1), X2) -> mark(__(X1, X2)),
                  __(ok(X1), ok(X2)) -> ok(__(X1, X2)),
                active(__(X, nil())) -> mark(X),
                  active(__(X1, X2)) -> __(X1, active(X2)),
                  active(__(X1, X2)) -> __(active(X1), X2),
             active(__(__(X, Y), Z)) -> mark(__(X, __(Y, Z))),
                active(__(nil(), X)) -> mark(X),
                      active(U12(X)) -> U12(active(X)),
                   active(U12(tt())) -> mark(tt()),
                      active(U11(X)) -> U11(active(X)),
                   active(U11(tt())) -> mark(U12(tt())),
                  active(isNePal(X)) -> isNePal(active(X)),
    active(isNePal(__(I, __(P, I)))) -> mark(U11(tt())),
                        U12(mark(X)) -> mark(U12(X)),
                          U12(ok(X)) -> ok(U12(X)),
                        U11(mark(X)) -> mark(U11(X)),
                          U11(ok(X)) -> ok(U11(X)),
                    isNePal(mark(X)) -> mark(isNePal(X)),
                      isNePal(ok(X)) -> ok(isNePal(X)),
                  proper(__(X1, X2)) -> __(proper(X1), proper(X2)),
                       proper(nil()) -> ok(nil()),
                      proper(U12(X)) -> U12(proper(X)),
                        proper(tt()) -> ok(tt()),
                      proper(U11(X)) -> U11(proper(X)),
                  proper(isNePal(X)) -> isNePal(proper(X)),
                        top(mark(X)) -> top(proper(X)),
                          top(ok(X)) -> top(active(X))
   }
  Fail