YES(?,PRIMREC)

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

Strict Trs:
  { fib(0()) -> 0()
  , fib(s(0())) -> s(0())
  , fib(s(s(x))) -> +(fib(s(x)), fib(x))
  , +(x, 0()) -> x
  , +(x, s(y)) -> s(+(x, y)) }
Obligation:
  innermost runtime complexity
Answer:
  YES(?,PRIMREC)

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

 fib > s, fib > +, 0 > s, 0 > +, + > s, fib ~ 0 .

Hurray, we answered YES(?,PRIMREC)