YES(?,ELEMENTARY)

'epo* (timeout of 60.0 seconds)'
--------------------------------
Answer:           YES(?,ELEMENTARY)
Input Problem:    innermost runtime-complexity with respect to
  Rules:
    {  rev(ls) -> r1(ls, empty())
     , r1(empty(), a) -> a
     , r1(cons(x, k), a) -> r1(k, cons(x, a))}

Proof Output:    
  Strict Rules in Predicative Notation:
   {  rev(ls;) -> r1(ls; empty())
    , r1(empty(); a) -> a
    , r1(cons(; x, k); a) -> r1(k; cons(; x, a))}
  Safe Mapping:
   safe(rev) = {}, safe(r1) = {2}, safe(empty) = {},
   safe(cons) = {1, 2}
  Argument Permutation:
   mu(rev) = [1], mu(r1) = [1, 2]
  Precedence:
   r1 ~ r1, rev > r1, rev ~ rev