intro dans_S_X.
elimtype (exists w : Word, word w = S').
intro x.
change (word x <> natural 0) in |- *.
discriminate.
apply Mots_X; assumption.
Qed.
Hint Resolve N_dans_S_X.

Lemma injproducg_V1 :
forall x : Elt, dans x V1 -> injproducg V1 x = injgauche x.