YES(?,O(n^1))

Problem:
 f(a(),f(a(),x)) -> f(a(),f(f(a(),a()),f(a(),x)))

Proof:
 Bounds Processor:
  bound: 2
  enrichment: match
  automaton:
   final states: {3}
   transitions:
    f1(8,3) -> 9*
    f1(8,11) -> 9,3
    f1(10,3) -> 11*
    f1(10,9) -> 11*
    f1(8,8) -> 10*
    a1() -> 8*
    f2(12,11) -> 13*
    f2(12,15) -> 9*
    f2(14,13) -> 15*
    f2(12,12) -> 14*
    f0(3,3) -> 3*
    a2() -> 12*
    a0() -> 3*
  problem:
   
  Qed