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+From iris.algebra Require Export gmap.
+From iris.algebra Require Import excl.
+From iris.prelude Require Import mapset.
+
+Definition gsetC K `{Countable K} := gmapC K (exclC unitC).
+
+Definition to_gsetC `{Countable K} (X : gset K) : gsetC K :=
+  to_gmap (Excl ()) X.
+
+Section gset.
+Context `{Countable K}.
+Implicit Types X Y : gset K.
+
+Lemma to_gsetC_empty : to_gsetC (∅ : gset K) = ∅.
+Proof. apply to_gmap_empty. Qed.
+Lemma to_gsetC_union X Y : X ⊥ Y → to_gsetC X ⋅ to_gsetC Y = to_gsetC (X ∪ Y).
+Proof.
+  intros HXY; apply: map_eq=> i; rewrite /to_gsetC /=.
+  rewrite lookup_op !lookup_to_gmap. repeat case_option_guard; set_solver.
+Qed.
+Lemma to_gsetC_valid X : ✓ to_gsetC X.
+Proof. intros i. rewrite /to_gsetC lookup_to_gmap. by case_option_guard. Qed.
+Lemma to_gsetC_valid_op X Y : ✓ (to_gsetC X ⋅ to_gsetC Y) ↔ X ⊥ Y.
+Proof.
+  split; last (intros; rewrite to_gsetC_union //; apply to_gsetC_valid).
+  intros HXY i ??; move: (HXY i); rewrite lookup_op !lookup_to_gmap.
+  rewrite !option_guard_True //.
+Qed.
+
+Context `{Fresh K (gset K), !FreshSpec K (gset K)}.
+Lemma updateP_alloc_strong (Q : gsetC K → Prop) (I : gset K) X :
+  (∀ i, i ∉ X → i ∉ I → Q (to_gsetC ({[i]} ∪ X))) → to_gsetC X ~~>: Q.
+Proof.
+  intros; apply updateP_alloc_strong with I (Excl ()); [done|]=> i.
+  rewrite /to_gsetC lookup_to_gmap_None -to_gmap_union_singleton; eauto.
+Qed.
+Lemma updateP_alloc (Q : gsetC K → Prop) X :
+  (∀ i, i ∉ X → Q (to_gsetC ({[i]} ∪ X))) → to_gsetC X ~~>: Q.
+Proof. move=>??. eapply updateP_alloc_strong with (I:=∅); by eauto. Qed.
+Lemma updateP_alloc_strong' (I : gset K) X :
+  to_gsetC X ~~>: λ Y : gsetC K, ∃ i, Y = to_gsetC ({[ i ]} ∪ X) ∧ i ∉ I ∧ i ∉ X.
+Proof. eauto using updateP_alloc_strong. Qed.
+Lemma updateP_alloc' X :
+  to_gsetC X ~~>: λ Y : gsetC K, ∃ i, Y = to_gsetC ({[ i ]} ∪ X) ∧ i ∉ X.
+Proof. eauto using updateP_alloc. Qed.
+End gset.
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