(** A list without redundancy modulo the equality over [A]. *)
#[local]
Hint Constructors NoDupA : core.
(** An alternative definition of [NoDupA] based on [ForallOrdPairs] *)

(* Specifications: *)
Lemma NoDupA_altdef : forall l,
NoDupA l <-> ForallOrdPairs (complement eqA) l.