YES

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

Proof:
 Bounds Processor:
  bound: 0
  enrichment: match
  automaton:
   final states: {1}
   transitions:
    f20() -> 2*
    a0(11) -> 12*
    a0(14) -> 15*
    a0(8) -> 9*
    b0(10) -> 11*
    b0(5) -> 6*
    b0(6) -> 7*
    b0(2) -> 3*
    b0(18) -> 19*
    b0(7) -> 8*
    b0(4) -> 5*
    b0(9) -> 10*
    b0(12) -> 13*
    b0(19) -> 1*
    b0(3) -> 4*
    b0(13) -> 14*
    b0(15) -> 16*
    b0(16) -> 17*
    b0(17) -> 18*
    1 -> 3,4,14
  problem:
   
  Qed