We are left with following problem, upon which TcT provides the
certificate YES(?,O(n^1)).

Strict Trs:
  { b(x, y) -> c(a(c(y), a(0(), x)))
  , a(y, x) -> y
  , a(y, c(b(a(0(), x), 0()))) -> b(a(c(b(0(), y)), x), 0()) }
Obligation:
  runtime complexity
Answer:
  YES(?,O(n^1))

The problem is match-bounded by 1. The enriched problem is
compatible with the following automaton.
{ b_0(2, 2) -> 1
, c_0(2) -> 1
, c_0(2) -> 2
, c_1(2) -> 3
, c_1(2) -> 4
, c_1(3) -> 1
, a_0(2, 2) -> 1
, a_1(4, 5) -> 3
, a_1(6, 2) -> 5
, 0_0() -> 1
, 0_0() -> 2
, 0_1() -> 5
, 0_1() -> 6 }

Hurray, we answered YES(?,O(n^1))