fact: CoInductive weak_eq : ACProcess -> ACProcess -> Prop := w_eq : forall p q : ACProcess, (forall (c : Chnl) (w : Signal c) (p' : ACProcess), Trans c p (Transmit c w) p' -> exists q' : ACProcess, weak_derivative c q w q' /\ weak_eq p' q') -> (forall (c : Chnl) (w : Signal c) (q' : ACProcess), Trans c q (Transmit c w) q' -> exists p' : ACProcess, weak_derivative c p w p' /\ weak_eq p' q') -> weak_eq p q.