MAYBE
Time: 0.130

Problem:
 Equations:
  plusAC(plusAC(x4,x5),x6) -> plusAC(x4,plusAC(x5,x6))
  plusAC(x4,x5) -> plusAC(x5,x4)
  sumAC(sumAC(x4,x5),x6) -> sumAC(x4,sumAC(x5,x6))
  sumAC(x4,x5) -> sumAC(x5,x4)
  plusAC(x4,plusAC(x5,x6)) -> plusAC(plusAC(x4,x5),x6)
  plusAC(x5,x4) -> plusAC(x4,x5)
  sumAC(x4,sumAC(x5,x6)) -> sumAC(sumAC(x4,x5),x6)
  sumAC(x5,x4) -> sumAC(x4,x5)
 TRS:
  plusAC(x,0()) -> x
  plusAC(x,s(y)) -> s(plusAC(x,y))
  sumAC(nil(),nil()) -> 0()
  sumAC(cons(x,xs),nil()) -> plusAC(x,sumAC(xs,nil()))
  sumAC(nil(),cons(x,xs)) -> plusAC(x,sumAC(nil(),xs))
  sumAC(cons(x,xs),cons(y,ys)) -> plusAC(plusAC(x,y),sumAC(xs,ys))

Proof:
 Open