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