TRS:
 {a(b(x)) -> b(a(x)),
  a(c(x)) -> x}
 POP*:
  Precedence:
  a > b
  empty
  
Normal:
   pi(a) = [1]
  
Safe:
   pi(c) = [1], pi(b) = [1]
  
Predicative System:
   {a(b(;x);) -> b(;a(x;)),
    a(c(;x);) -> x}
  Qed