YES
Time: 0.016

Problem:
 Equations:
  pAC(pAC(x3,x4),x5) -> pAC(x3,pAC(x4,x5))
  pAC(x3,x4) -> pAC(x4,x3)
  pAC(x3,pAC(x4,x5)) -> pAC(pAC(x3,x4),x5)
  pAC(x4,x3) -> pAC(x3,x4)
 TRS:
  pAC(x,zero()) -> x
  pAC(pAC(pAC(pAC(a(),a()),b()),b()),b()) -> pAC(pAC(pAC(a(),a()),a()),b())
  pAC(pAC(pAC(pAC(a(),a()),a()),a()),b()) -> pAC(pAC(pAC(a(),a()),b()),b())

Proof:
 AC-KBO Processor:
  precedence:
   b ~ pAC > a ~ zero
   weight function:
    w0 = 1
    w(a) = 6
    w(zero) = 4
    w(b) = w(pAC) = 2
   problem:
    Equations:
     pAC(pAC(x3,x4),x5) -> pAC(x3,pAC(x4,x5))
     pAC(x3,x4) -> pAC(x4,x3)
     pAC(x3,pAC(x4,x5)) -> pAC(pAC(x3,x4),x5)
     pAC(x4,x3) -> pAC(x3,x4)
    TRS:
     
   Qed