Hint Resolve degree_exp_wrt_exp_O : lngen.
(* begin hide *)

Lemma degree_exp_wrt_exp_close_exp_wrt_exp_rec_mutual :
(forall e1 x1 n1,
degree_exp_wrt_exp n1 e1 ->
degree_exp_wrt_exp (S n1) (close_exp_wrt_exp_rec n1 x1 e1)).