Section Properties.
Implicit Types x y : TVar.
Implicit Types xs ys : list TVar.
(* ---------------------------------------------------------------------- *)
(** **** Abstract properties of ok *)
(* ---------------------------------------------------------------------- *)
(** **** Properties of binds *)

(** Binds and update. *)
Theorem binds_update_notin : forall A x (v : A) (F G : gen_env A),
x ∹ v ⋲ F ->
x ∉ G ->
x ∹ v ⋲ (F ::= G).