TIMEOUT
MAYBE
Trs:
 {      f(a(x), y) -> f(x, a(y)),
        f(b(x), y) -> f(x, b(y)),
        f(c(x), y) -> f(x, c(y)),
  f(x, a(b(c(y)))) -> f(b(c(a(b(x)))), y)}
 Open