Definition term_of (m : msg) :=
    match m with
      | RequestVote t _ _ _ => Some t
      | RequestVoteReply t _ => Some t
      | AppendEntries t _ _ _ _ _ => Some t
      | AppendEntriesReply t _ _ => Some t
    end.

Lemma removeAfterIndex_partition : forall l x, exists l', l = l' ++ removeAfterIndex l x.