Definition l_inclus (l1 l2 : wordset) : Prop := forall w : Word, l1 w -> l2 w.

(* Specifications: *)
Lemma refl_l_inclus : forall l1 : wordset, l_inclus l1 l1.
Lemma trans_l_inclus : forall l1 l2 l3 : wordset, l_inclus l1 l2 -> l_inclus l2 l3 -> l_inclus l1 l3.