YES(?,ELEMENTARY)

'epo* (timeout of 60.0 seconds)'
--------------------------------
Answer:           YES(?,ELEMENTARY)
Input Problem:    innermost runtime-complexity with respect to
  Rules:
    {  fst(0(), Z) -> nil()
     , fst(s(), cons(Y)) -> cons(Y)
     , from(X) -> cons(X)
     , add(0(), X) -> X
     , add(s(), Y) -> s()
     , len(nil()) -> 0()
     , len(cons(X)) -> s()}

Proof Output:    
  Strict Rules in Predicative Notation:
   {  fst(0(); Z) -> nil()
    , fst(s(); cons(; Y)) -> cons(; Y)
    , from(; X) -> cons(; X)
    , add(; 0(), X) -> X
    , add(; s(), Y) -> s()
    , len(nil();) -> 0()
    , len(cons(; X);) -> s()}
  Safe Mapping:
   safe(fst) = {2}, safe(0) = {}, safe(nil) = {}, safe(s) = {},
   safe(cons) = {1}, safe(from) = {1}, safe(add) = {1, 2},
   safe(len) = {}
  Argument Permutation:
   mu(fst) = [2, 1], mu(from) = [1], mu(add) = [2, 1], mu(len) = [1]
  Precedence:
   len ~ len, len ~ fst, add > len, add ~ add, add > fst, from > len,
   from > add, from ~ from, from > fst, fst ~ len, fst ~ fst