TRS:
 {   f(c(s(x), y)) -> f(c(x, s(y))),
  f(c(s(x), s(y))) -> g(c(x, y)),
     g(c(x, s(y))) -> g(c(s(x), y)),
  g(c(s(x), s(y))) -> f(c(x, y))}
 Fail