YES(?,O(n^1))

Problem:
 a(a(b(x1))) -> b(a(b(x1)))
 b(a(x1)) -> a(b(b(x1)))
 b(c(a(x1))) -> c(c(a(a(b(x1)))))

Proof:
 Bounds Processor:
  bound: 0
  enrichment: match
  automaton:
   final states: {3,2}
   transitions:
    a0(1) -> 2*
    b0(1) -> 3*
    c0(1) -> 1*
  problem:
   
  Qed