YES(?,ELEMENTARY)

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

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