proposition: Lemma union_Xim_Vim_map_f_union_X_V : union Xim Vim = map f (union X V) :>Ensf.
proof: Proof. unfold Xim, Vim, Gim2, Gim, imageGram in |- *; simpl in |- *. apply map_union. Qed.
imports: Ensf Words more_words need fonctions Relations gram gram2