Global Instance eqL_equivalence : Equivalence EqL.

(* Specifications: *)
Lemma ex_lg : forall A B, exists l, Q_Cong l /\ l A B.
Lemma lg_eql_lg : forall l1 l2, Q_Cong l1 -> EqL l1 l2 -> Q_Cong l2.
Lemma ex_eqL : forall l1 l2, Q_Cong l1 -> Q_Cong l2 -> (exists A, exists B, l1 A B /\ l2 A B) -> EqL l1 l2.