Proof using.
induction l; intros; simpl in *.
- find_inversion. simpl in *. intuition.
- break_match. find_inversion. simpl in *.
intuition; subst; simpl in *; eauto;
subst; eapply processPackets_correct in Heqp; eauto; omega.
Qed.

(* Specifications: *)
Lemma processPackets_NoDup : forall n l n' l',
processPackets n l = (n', l') ->
NoDup l'.