YES(?,ELEMENTARY)

'epo* (timeout of 60.0 seconds)'
--------------------------------
Answer:           YES(?,ELEMENTARY)
Input Problem:    innermost runtime-complexity with respect to
  Rules:
    {  fib(0()) -> 0()
     , fib(s(0())) -> s(0())
     , fib(s(s(x))) -> +(fib(s(x)), fib(x))}

Proof Output:    
  Strict Rules in Predicative Notation:
   {  fib(0();) -> 0()
    , fib(s(; 0());) -> s(; 0())
    , fib(s(; s(; x));) -> +(; fib(s(; x);), fib(x;))}
  Safe Mapping:
   safe(fib) = {}, safe(0) = {}, safe(s) = {1}, safe(+) = {1, 2}
  Argument Permutation:
   mu(fib) = [1]
  Precedence:
   fib ~ fib