Inductive D_queue : queue Message -> Prop :=
  | D_empty : D_queue (empty Message)
  | D_dec :
      forall qm : queue Message,
      alternate qm -> D_queue (input Message dec qm).Inductive D_queue : queue Message -> Prop :=
  | D_empty : D_queue (empty Message)
  | D_dec :
      forall qm : queue Message,
      alternate qm -> D_queue (input Message dec qm).Inductive D_queue : queue Message -> Prop :=
  | D_empty : D_queue (empty Message)
  | D_dec :
      forall qm : queue Message,
      alternate qm -> D_queue (input Message dec qm).

Lemma alt_post_any : forall m : Message, (forall s : Site, m <> inc_dec s) -> alternate (b0 s0 owner) -> alternate (Post_message Message m b0 s0 owner s0 owner).