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 argmax_fun_ext : forall A (f : A -> nat) g l, (forall a, f a = g a) -> argmax f l = argmax g l.