MAYBE
MAYBE
TRS:
 {
                    mark(nil()) -> active(nil()),
              mark(fst(X1, X2)) -> active(fst(mark(X1), mark(X2))),
                      mark(0()) -> active(0()),
             mark(cons(X1, X2)) -> active(cons(mark(X1), X2)),
                     mark(s(X)) -> active(s(X)),
                  mark(from(X)) -> active(from(mark(X))),
              mark(add(X1, X2)) -> active(add(mark(X1), mark(X2))),
                   mark(len(X)) -> active(len(mark(X))),
            active(fst(0(), Z)) -> mark(nil()),
  active(fst(s(X), cons(Y, Z))) -> mark(cons(Y, fst(X, Z))),
                active(from(X)) -> mark(cons(X, from(s(X)))),
            active(add(0(), X)) -> mark(X),
           active(add(s(X), Y)) -> mark(s(add(X, Y))),
             active(len(nil())) -> mark(0()),
        active(len(cons(X, Z))) -> mark(s(len(Z))),
              fst(X1, mark(X2)) -> fst(X1, X2),
            fst(X1, active(X2)) -> fst(X1, X2),
              fst(mark(X1), X2) -> fst(X1, X2),
            fst(active(X1), X2) -> fst(X1, X2),
             cons(X1, mark(X2)) -> cons(X1, X2),
           cons(X1, active(X2)) -> cons(X1, X2),
             cons(mark(X1), X2) -> cons(X1, X2),
           cons(active(X1), X2) -> cons(X1, X2),
                     s(mark(X)) -> s(X),
                   s(active(X)) -> s(X),
                  from(mark(X)) -> from(X),
                from(active(X)) -> from(X),
              add(X1, mark(X2)) -> add(X1, X2),
            add(X1, active(X2)) -> add(X1, X2),
              add(mark(X1), X2) -> add(X1, X2),
            add(active(X1), X2) -> add(X1, X2),
                   len(mark(X)) -> len(X),
                 len(active(X)) -> len(X)
 }
 DUP: We consider a duplicating system.
  Trs:
   {
                      mark(nil()) -> active(nil()),
                mark(fst(X1, X2)) -> active(fst(mark(X1), mark(X2))),
                        mark(0()) -> active(0()),
               mark(cons(X1, X2)) -> active(cons(mark(X1), X2)),
                       mark(s(X)) -> active(s(X)),
                    mark(from(X)) -> active(from(mark(X))),
                mark(add(X1, X2)) -> active(add(mark(X1), mark(X2))),
                     mark(len(X)) -> active(len(mark(X))),
              active(fst(0(), Z)) -> mark(nil()),
    active(fst(s(X), cons(Y, Z))) -> mark(cons(Y, fst(X, Z))),
                  active(from(X)) -> mark(cons(X, from(s(X)))),
              active(add(0(), X)) -> mark(X),
             active(add(s(X), Y)) -> mark(s(add(X, Y))),
               active(len(nil())) -> mark(0()),
          active(len(cons(X, Z))) -> mark(s(len(Z))),
                fst(X1, mark(X2)) -> fst(X1, X2),
              fst(X1, active(X2)) -> fst(X1, X2),
                fst(mark(X1), X2) -> fst(X1, X2),
              fst(active(X1), X2) -> fst(X1, X2),
               cons(X1, mark(X2)) -> cons(X1, X2),
             cons(X1, active(X2)) -> cons(X1, X2),
               cons(mark(X1), X2) -> cons(X1, X2),
             cons(active(X1), X2) -> cons(X1, X2),
                       s(mark(X)) -> s(X),
                     s(active(X)) -> s(X),
                    from(mark(X)) -> from(X),
                  from(active(X)) -> from(X),
                add(X1, mark(X2)) -> add(X1, X2),
              add(X1, active(X2)) -> add(X1, X2),
                add(mark(X1), X2) -> add(X1, X2),
              add(active(X1), X2) -> add(X1, X2),
                     len(mark(X)) -> len(X),
                   len(active(X)) -> len(X)
   }
  Fail