intros x dans_x_V2.
unfold injproducd, extension in |- *.
elim (extension_spec V2 injdroite x).
intros x0 temp; elim temp; clear temp; intro temp; elim temp; clear temp.
auto.
intros.
absurd (dans x V2); assumption.
Qed.
Hint Resolve injproducd_V2.

Lemma map_injproducd_V2 : map (injproducd V2) V2 = map injdroite V2 :>Ensf.
apply map_egal.