TIMEOUT
MAYBE
Trs:
 {U12(tt(), M, N) -> s(plus(activate(N), activate(M))),
     plus(N, 0()) -> N,
    plus(N, s(M)) -> U11(tt(), M, N),
  U11(tt(), M, N) -> U12(tt(), activate(M), activate(N)),
      activate(X) -> X}
 Open