Internalize equality property for agree.

algebra/agree.v

@@ -131,6 +131,8 @@ Lemma to_agree_car n (x : agree A) : ✓{n} x → to_agree (x n) ≡{n}≡ x.
 Proof. intros [??]; split; naive_solver eauto using agree_valid_le. Qed.
 
 (** Internalized properties *)
+Lemma agree_equivI {M} a b : (to_agree a ≡ to_agree b)%I ≡ (a ≡ b : uPred M)%I.
+Proof. split. by intros [? Hv]; apply (Hv n). apply: to_agree_ne. Qed.
 Lemma agree_validI {M} x y : ✓ (x ⋅ y) ⊑ (x ≡ y : uPred M).
 Proof. by intros r n _ ?; apply: agree_op_inv. Qed.
 End agree.