Require Export List.
Require Lt.
Definition all_equiv (l: list Prop) :=
forall x y, In x l -> In y l -> (x <-> y).
Definition all_equiv'_aux (l: list Prop) : Prop.
Definition all_equiv' (l: list Prop) : Prop.
*)

Lemma all_equiv__equiv : forall l, all_equiv l <-> all_equiv' l.