unfold Derivestar_P_A_3, Rstar in |- *.
intros x y x' y' s s' Der_star.
change
((fun a a' : Word * Conf =>
inmonoid X (fst a) ->
Derivegstar X R (Append (fst a) (fst (snd a)))
(Append (fst a') (fst (snd a')))) (s, (x, y))
(s', (x', y'))) in |- *.
apply Der_star; unfold Derivegstar in |- *.
intros.
apply Rstar_reflexive.
intros u v w.
elim u. intros u1 uc. elim uc. intros u2 u3.
elim v. intros v1 vc. elim vc. intros v2 v3.
simpl in |- *.
intros Der_3_u_v Hyp inmon_u1.
apply Rstar_transitive with (Append v1 v2).
change (Derivegstar X R (Append u1 u2) (Append v1 v2)) in |- *.
apply Derive_P_A_3_imp_Derivegstar with u3 v3.
assumption.
assumption.
apply Hyp.
apply Derive_P_A_3_conserve_inmonoid_s with u2 u3 v2 v3 u1.
assumption.
assumption.
Qed.
(*Tout mot reconnu par l'automate est reconnu par la grammaire*)

Theorem Derivestar_P_A_imp_Derivestar :
forall x y : Word, Derivestar_P_A X d (x, y) (nil, nil) -> Derivestar R x y.