Definition no_msg_from_imp from to d :
no_msg_from from d -> no_msg_from_to from to d.

Lemma msg_specE'' s from from' to to' tg cnt tms :
valid s -> from == from' = false ->
msg_spec from to tg cnt s ->
msg_spec from to tg cnt (post_msg s (Msg tms from' to' true)).1.