intros x y Der.
elim Der.
intros w u x0 dans_x0_X.
replace (cons x0 w) with (Append (cons x0 nil) w).
pattern w at 2 in |- *.
replace w with (Append nil w).
apply Derive_cons.
assumption.
unfold d in |- *.
apply union_d.
change (dans (f_X_d x0) (map f_X_d X)) in |- *.
apply dans_map_inv.
assumption.
trivial.
trivial.
intros v w u x0 dans_couple.
replace (cons x0 w) with (Append (cons x0 nil) w).
apply Derive_eps.
unfold d in |- *.
apply union_g.
replace (couple (word (cons x0 nil)) (couple (eps X) (word u))) with
(f_R_d (couple x0 (word u))).
apply dans_map_inv.
assumption.
unfold f_R_d in |- *.
trivial.
trivial.
Qed.
Hint Resolve Derive_P_A_2_imp_Derive_P_A.

(* Specifications: *)
Lemma Derivestar_P_A_2_imp_Derivestar_P_A :
forall x y : Word * Word, Derivestar_P_A_2 x y -> Derivestar_P_A X d x y.