TRS:
 {                 a__from(X) -> cons(mark(X), from(s(X))),
            a__after(0(), XS) -> mark(XS),
  a__after(s(N), cons(X, XS)) -> a__after(mark(N), mark(XS)),
                mark(from(X)) -> a__from(mark(X)),
          mark(after(X1, X2)) -> a__after(mark(X1), mark(X2)),
           mark(cons(X1, X2)) -> cons(mark(X1), X2),
                   mark(s(X)) -> s(mark(X)),
                    mark(0()) -> 0(),
                   a__from(X) -> from(X),
             a__after(X1, X2) -> after(X1, X2)}
 Fail