Problem:
 a() -> b()
 a() -> f(a())
 b() -> f(f(b()))

Proof:
 Nonconfluence Processor:
  terms: f(f(b())) *<- a() ->* f(b())
  Qed
  
  first automaton:
   final states: {4}
   transitions:
    b() -> 5*
    f(6) -> 5,4
    f(5) -> 6*
  
  second automaton:
   final states: {7}
   transitions:
    b() -> 8*
    f(7) -> 8*
    f(8) -> 7*