(* subst_rec_subst_rec *)

(* Specifications: *)
Lemma subst_rec_subst_rec :
forall (U V W : redexes) (n p : nat),
subst_rec_r (subst_rec_r V U p) W (p + n) =
subst_rec_r (subst_rec_r V W (S (p + n))) (subst_rec_r U W n) p.
Lemma subst_rec_subst_0 :
forall (U V W : redexes) (n : nat),
subst_rec_r (subst_rec_r V U 0) W n =
subst_rec_r (subst_rec_r V W (S n)) (subst_rec_r U W n) 0.