YES(?,O(n^1))

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

Proof:
 Bounds Processor:
  bound: 0
  enrichment: match
  automaton:
   final states: {5,4,3,2}
   transitions:
    a0(1) -> 2*
    d0(1) -> 5*
    c0(1) -> 4*
    b0(1) -> 3*
    f80() -> 1*
  problem:
   
  Qed