MAYBE
MAYBE
TRS:
 {
            mark(U11(X1, X2)) -> active(U11(mark(X1), X2)),
                   mark(tt()) -> active(tt()),
                   mark(s(X)) -> active(s(mark(X))),
           mark(plus(X1, X2)) -> active(plus(mark(X1), mark(X2))),
        mark(U21(X1, X2, X3)) -> active(U21(mark(X1), X2, X3)),
            mark(and(X1, X2)) -> active(and(mark(X1), X2)),
               mark(isNat(X)) -> active(isNat(X)),
                    mark(0()) -> active(0()),
         active(U11(tt(), N)) -> mark(N),
        active(plus(N, s(M))) -> mark(U21(and(isNat(M), isNat(N)), M, N)),
         active(plus(N, 0())) -> mark(U11(isNat(N), N)),
      active(U21(tt(), M, N)) -> mark(s(plus(N, M))),
         active(and(tt(), X)) -> mark(X),
         active(isNat(s(V1))) -> mark(isNat(V1)),
  active(isNat(plus(V1, V2))) -> mark(and(isNat(V1), isNat(V2))),
           active(isNat(0())) -> mark(tt()),
            U11(X1, mark(X2)) -> U11(X1, X2),
          U11(X1, active(X2)) -> U11(X1, X2),
            U11(mark(X1), X2) -> U11(X1, X2),
          U11(active(X1), X2) -> U11(X1, X2),
                   s(mark(X)) -> s(X),
                 s(active(X)) -> s(X),
           plus(X1, mark(X2)) -> plus(X1, X2),
         plus(X1, active(X2)) -> plus(X1, X2),
           plus(mark(X1), X2) -> plus(X1, X2),
         plus(active(X1), X2) -> plus(X1, X2),
        U21(X1, X2, mark(X3)) -> U21(X1, X2, X3),
      U21(X1, X2, active(X3)) -> U21(X1, X2, X3),
        U21(X1, mark(X2), X3) -> U21(X1, X2, X3),
      U21(X1, active(X2), X3) -> U21(X1, X2, X3),
        U21(mark(X1), X2, X3) -> U21(X1, X2, X3),
      U21(active(X1), X2, X3) -> U21(X1, X2, X3),
            and(X1, mark(X2)) -> and(X1, X2),
          and(X1, active(X2)) -> and(X1, X2),
            and(mark(X1), X2) -> and(X1, X2),
          and(active(X1), X2) -> and(X1, X2),
               isNat(mark(X)) -> isNat(X),
             isNat(active(X)) -> isNat(X)
 }
 DUP: We consider a duplicating system.
  Trs:
   {
              mark(U11(X1, X2)) -> active(U11(mark(X1), X2)),
                     mark(tt()) -> active(tt()),
                     mark(s(X)) -> active(s(mark(X))),
             mark(plus(X1, X2)) -> active(plus(mark(X1), mark(X2))),
          mark(U21(X1, X2, X3)) -> active(U21(mark(X1), X2, X3)),
              mark(and(X1, X2)) -> active(and(mark(X1), X2)),
                 mark(isNat(X)) -> active(isNat(X)),
                      mark(0()) -> active(0()),
           active(U11(tt(), N)) -> mark(N),
          active(plus(N, s(M))) -> mark(U21(and(isNat(M), isNat(N)), M, N)),
           active(plus(N, 0())) -> mark(U11(isNat(N), N)),
        active(U21(tt(), M, N)) -> mark(s(plus(N, M))),
           active(and(tt(), X)) -> mark(X),
           active(isNat(s(V1))) -> mark(isNat(V1)),
    active(isNat(plus(V1, V2))) -> mark(and(isNat(V1), isNat(V2))),
             active(isNat(0())) -> mark(tt()),
              U11(X1, mark(X2)) -> U11(X1, X2),
            U11(X1, active(X2)) -> U11(X1, X2),
              U11(mark(X1), X2) -> U11(X1, X2),
            U11(active(X1), X2) -> U11(X1, X2),
                     s(mark(X)) -> s(X),
                   s(active(X)) -> s(X),
             plus(X1, mark(X2)) -> plus(X1, X2),
           plus(X1, active(X2)) -> plus(X1, X2),
             plus(mark(X1), X2) -> plus(X1, X2),
           plus(active(X1), X2) -> plus(X1, X2),
          U21(X1, X2, mark(X3)) -> U21(X1, X2, X3),
        U21(X1, X2, active(X3)) -> U21(X1, X2, X3),
          U21(X1, mark(X2), X3) -> U21(X1, X2, X3),
        U21(X1, active(X2), X3) -> U21(X1, X2, X3),
          U21(mark(X1), X2, X3) -> U21(X1, X2, X3),
        U21(active(X1), X2, X3) -> U21(X1, X2, X3),
              and(X1, mark(X2)) -> and(X1, X2),
            and(X1, active(X2)) -> and(X1, X2),
              and(mark(X1), X2) -> and(X1, X2),
            and(active(X1), X2) -> and(X1, X2),
                 isNat(mark(X)) -> isNat(X),
               isNat(active(X)) -> isNat(X)
   }
  Fail