MAYBE

We are left with following problem, upon which TcT provides the
certificate MAYBE.

Strict Trs:
  { numbers() -> d(0())
  , d(x) -> if(le(x, nr()), x)
  , if(true(), x) -> cons(x, d(s(x)))
  , if(false(), x) -> nil()
  , le(0(), y) -> true()
  , le(s(x), 0()) -> false()
  , le(s(x), s(y)) -> le(x, y)
  , nr() -> ack(s(s(s(s(s(s(0())))))), 0())
  , ack(0(), x) -> s(x)
  , ack(s(x), 0()) -> ack(x, s(0()))
  , ack(s(x), s(y)) -> ack(x, ack(s(x), y)) }
Obligation:
  innermost runtime complexity
Answer:
  MAYBE

The input cannot be shown compatible

Arrrr..