YES(?,ELEMENTARY)

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

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