YES(?,ELEMENTARY)

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

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