YES(?,O(n^1))

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

Proof:
 RT Transformation Processor:
  strict:
   f(f(x,a()),y) -> f(f(a(),y),f(a(),x))
  weak:
   
  Bounds Processor:
   bound: 1
   enrichment: match-rt
   automaton:
    final states: {3}
    transitions:
     f1(9,8) -> 3*
     f1(7,3) -> 9,8
     f1(7,7) -> 8*
     f1(7,8) -> 9*
     a1() -> 7*
     f0(3,3) -> 3*
     a0() -> 3*
   problem:
    strict:
     
    weak:
     f(f(x,a()),y) -> f(f(a(),y),f(a(),x))
   Qed