YES(?,O(n^1))

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

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