simple induction e.
intros.
inversion_clear H; inversion_clear H0; trivial.
intros.
inversion_clear H0; inversion_clear H1.
elim (H s s0 H2 H0); trivial.
Qed.
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(*  The Acces predicate is defined using the notion of Squelette             *)
(* It describes how to reach an identifier in an environment                 *)
(*****************************************************************************)
Inductive Access : Pat -> Squelette -> Commande -> Prop :=
| Rule1 :
forall (P : Pat) (s : Squelette), Access P (cons_squelette P s) cdr
| Rule2 :
forall (P T : Pat) (s : Squelette) (C : Commande),
P <> T -> Access P s C -> Access P (cons_squelette T s) (o car C).
(*****************************************************************************)
(*   The following small lemma shows that Access is injective                *)
(*****************************************************************************)

Lemma Access_inject :
forall (x : Pat) (s : Squelette) (C C' : Commande),
Access x s C' -> Access x s C -> C = C' :>Commande.