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

Lemma findA_rev : forall l k, NoDupA eqk l ->
findA (eqb k) l = findA (eqb k) (rev l).