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