(* lemmes sur Ndouble, Ndouble_plus_one *)

(* Specifications: *)
Lemma Ndouble_inv_N0 : forall x : ad, Ndouble x = N0 -> x = N0.
Lemma Ndouble_inv_xO :
forall (x : ad) (p : positive), Ndouble x = Npos (xO p) -> x = Npos p.
Lemma Ndouble_plus_one_inv_xH :
forall x : ad, Ndouble_plus_one x = Npos 1 -> x = N0.
Lemma Ndouble_plus_one_inv_xI :
forall (x : ad) (p : positive),
Ndouble_plus_one x = Npos (xI p) -> x = Npos p.