unfold inter in |- *.
split; [ auto | split ].
auto.
replace (map (injproducg V1) V1) with (map injgauche V1).
replace (map (injproducd V2) V2) with (map injdroite V2).
intros x dans_map_1 dans_map_2.
elimtype (exists y : Elt, dans y V1 /\ x = injgauche y).
elimtype (exists y : Elt, dans y V2 /\ x = injdroite y).
intros x2 temp; elim temp; clear temp; intros dans_x2_V2 egal_x2.
intros x1 temp; elim temp; clear temp; intros dans_x1_V1 egal_x1.
absurd (zero = un).
unfold zero, un in |- *.
red in |- *.
intro.
cut (0 = 1 :>nat).
change (0 <> 1 :>nat) in |- *.
auto.
change (natural_inv (natural 0) = natural_inv (natural 1) :>nat) in |- *.
apply (f_equal natural_inv); assumption.
apply couple_couple_inv2 with x1 x2.
replace (couple x1 zero) with x.
auto.
apply dans_map; assumption.
apply dans_map; assumption.
auto.
auto.
Qed.
Hint Resolve inter_V1'_V2'_empty.

Lemma egal_LG_u_1'_2' :
l_egal (LG X Vu Ru S') (lunion (LG X V1' R1' S1') (LG X V2' R2' S2')).