induction n; intuition; simpl in *.
omega.
intuition.
destruct (lt_dec i n).
right.
eapply IHn.
trivial.
left.
omega.
intuition.
eapply lt_trans.
eapply IHn.
trivial.
omega.
Qed.

(* Specifications: *)
Lemma forNats_NoDup :
forall n,
NoDup (forNats n).