(** The function [dom] computes the domain of an environment, returning a finite set of [atom]s. Note that we cannot use Coq's equality for finite sets, we must instead use a defined relation [=] for atom set equality. *)

(* Specifications: *)
Lemma dom_demo : forall (x y : atom) (T : typ),
dom (x ~ T) [=] singleton x.
Lemma dom_demo : forall (x y : atom) (T : typ),
dom (x ~ T) [=] singleton x.