Section M_ACTION.
Variable Message : Set.
Let Bag_of_message := Bag_of_Data Message.
(* This is taken straight from Jean's file *)
Definition Post_message (m0 : Message) (b0 : Bag_of_message)
(s0 s1 : Site) :=
change_queue (queue Message) b0 s0 s1 (input Message m0 (b0 s0 s1)).
Definition Collect_message (b0 : Bag_of_message) (s0 s1 : Site) :=
change_queue (queue Message) b0 s0 s1 (first_out Message (b0 s0 s1)).

Lemma collect_elsewhere :
forall (b0 : Bag_of_message) (s0 s1 s2 s3 : Site),
s0 <> s2 \/ s1 <> s3 -> Collect_message b0 s0 s1 s2 s3 = b0 s2 s3.