Notation eqke := (@eq_key_elt elt).
Notation eqk := (@eq_key elt).
Instance eqk_equiv : Equivalence eqk.
(** Complements about InA, NoDupA and findA *)

Lemma InA_eqke_eqk : forall k1 k2 e1 e2 l,
E.eq k1 k2 -> InA eqke (k1,e1) l -> InA eqk (k2,e2) l.