YES
Time: 0.028

Problem:
 Equations:
  fAC(fAC(x2,x3),x4) -> fAC(x2,fAC(x3,x4))
  fAC(x2,x3) -> fAC(x3,x2)
  fAC(x2,fAC(x3,x4)) -> fAC(fAC(x2,x3),x4)
  fAC(x3,x2) -> fAC(x2,x3)
 TRS:
  fAC(g(fAC(h(a()),a())),a()) -> fAC(h(a()),fAC(a(),a()))
  fAC(h(a()),g(a())) -> fAC(g(h(a())),a())
  fAC(g(h(a())),fAC(fAC(a(),a()),a())) -> fAC(g(fAC(h(a()),a())),a())
  fAC(h(a()),a()) -> fAC(h(a()),b())
  fAC(i(x,y),fAC(a(),y)) -> fAC(g(i(x,y)),y)

Proof:
 AC-RPO Processor:
  precedence:
   a > i > b > h > fAC > g
  status:
   i:mul  
  problem:
   Equations:
    fAC(fAC(x2,x3),x4) -> fAC(x2,fAC(x3,x4))
    fAC(x2,x3) -> fAC(x3,x2)
    fAC(x2,fAC(x3,x4)) -> fAC(fAC(x2,x3),x4)
    fAC(x3,x2) -> fAC(x2,x3)
   TRS:
    
  Qed