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

Proof:
 Nonconfluence Processor:
  terms: f(f(b())) *<- f(f(c())) ->* a()
  Qed
  
  first automaton:
   final states: {1}
   transitions:
    b() -> 2*
    f(3) -> 2,1
    f(2) -> 3*
  
  second automaton:
   final states: {4}
   transitions:
    a() -> 4*