YES(?,PRIMREC)

We are left with following problem, upon which TcT provides the
certificate YES(?,PRIMREC).

Strict Trs:
  { zeros() -> cons(0(), n__zeros())
  , zeros() -> n__zeros()
  , tail(cons(X, XS)) -> activate(XS)
  , activate(X) -> X
  , activate(n__zeros()) -> zeros() }
Obligation:
  innermost runtime complexity
Answer:
  YES(?,PRIMREC)

The input was oriented with the instance of'multiset path order' as
induced by the precedence

 zeros > cons, zeros > 0, zeros > n__zeros, tail > cons, tail > 0,
 tail > n__zeros, activate > cons, activate > 0,
 activate > n__zeros, zeros ~ tail, zeros ~ activate, cons ~ 0,
 cons ~ n__zeros, 0 ~ n__zeros, tail ~ activate .

Hurray, we answered YES(?,PRIMREC)