MAYBE

'Pop* (timeout of 60.0 seconds)'
--------------------------------
Answer:           MAYBE
Input Problem:    innermost runtime-complexity with respect to
  Rules:
    {  sub(0(), 0()) -> 0()
     , sub(s(x), 0()) -> s(x)
     , sub(0(), s(x)) -> 0()
     , sub(s(x), s(y)) -> sub(x, y)
     , zero(nil()) -> zero2(0(), nil())
     , zero(cons(x, xs)) -> zero2(sub(x, x), cons(x, xs))
     , zero2(0(), nil()) -> nil()
     , zero2(0(), cons(x, xs)) -> cons(sub(x, x), zero(xs))
     , zero2(s(y), nil()) -> zero(nil())
     , zero2(s(y), cons(x, xs)) -> zero(cons(x, xs))}

Proof Output:    
  The input cannot be shown compatible