diff --git a/opam b/opam
index 1e123ae371552c6fa48c7709547948642812b54f..2ddb3184735328798d520c2b65a7decf74c14bda 100644
--- a/opam
+++ b/opam
@@ -11,5 +11,5 @@ install: [make "install"]
 remove: ["rm" "-rf" "%{lib}%/coq/user-contrib/iris"]
 depends: [
   "coq" { (>= "8.7.1" & < "8.10~") | (= "dev") }
-  "coq-stdpp" { (= "dev.2019-02-20.2.c8c298d4") | (= "dev") }
+  "coq-stdpp" { (= "dev.2019-02-21.1.5eabf109") | (= "dev") }
 ]
diff --git a/theories/algebra/big_op.v b/theories/algebra/big_op.v
index e559caedf7cb3fbc7a2be4c3c4aa0bd56e116cbe..5695cb52a013c505f8e5effb64efb8314efbf9c2 100644
--- a/theories/algebra/big_op.v
+++ b/theories/algebra/big_op.v
@@ -381,9 +381,9 @@ Section gmultiset.
   Lemma big_opMS_empty f : ([^o mset] x ∈ ∅, f x) = monoid_unit.
   Proof. by rewrite /big_opMS gmultiset_elements_empty. Qed.
 
-  Lemma big_opMS_union f X Y :
-    ([^o mset] y ∈ X ∪ Y, f y) ≡ ([^o mset] y ∈ X, f y) `o` [^o mset] y ∈ Y, f y.
-  Proof. by rewrite /big_opMS gmultiset_elements_union big_opL_app. Qed.
+  Lemma big_opMS_disj_union f X Y :
+    ([^o mset] y ∈ X ⊎ Y, f y) ≡ ([^o mset] y ∈ X, f y) `o` [^o mset] y ∈ Y, f y.
+  Proof. by rewrite /big_opMS gmultiset_elements_disj_union big_opL_app. Qed.
 
   Lemma big_opMS_singleton f x : ([^o mset] y ∈ {[ x ]}, f y) ≡ f x.
   Proof.
@@ -393,14 +393,14 @@ Section gmultiset.
   Lemma big_opMS_delete f X x :
     x ∈ X → ([^o mset] y ∈ X, f y) ≡ f x `o` [^o mset] y ∈ X ∖ {[ x ]}, f y.
   Proof.
-    intros. rewrite -big_opMS_singleton -big_opMS_union.
-    by rewrite -gmultiset_union_difference'.
+    intros. rewrite -big_opMS_singleton -big_opMS_disj_union.
+    by rewrite -gmultiset_disj_union_difference'.
   Qed.
 
   Lemma big_opMS_unit X : ([^o mset] y ∈ X, monoid_unit) ≡ (monoid_unit : M).
   Proof.
     induction X using gmultiset_ind;
-      rewrite /= ?big_opMS_union ?big_opMS_singleton ?left_id //.
+      rewrite /= ?big_opMS_disj_union ?big_opMS_singleton ?left_id //.
   Qed.
 
   Lemma big_opMS_opMS f g X :
@@ -478,7 +478,7 @@ Section homomorphisms.
   Proof.
     intros. induction X as [|x X IH] using gmultiset_ind.
     - by rewrite !big_opMS_empty monoid_homomorphism_unit.
-    - by rewrite !big_opMS_union !big_opMS_singleton monoid_homomorphism -IH.
+    - by rewrite !big_opMS_disj_union !big_opMS_singleton monoid_homomorphism -IH.
   Qed.
   Lemma big_opMS_commute1 `{Countable A} (h : M1 → M2)
       `{!WeakMonoidHomomorphism o1 o2 R h} (f : A → M1) X :
@@ -486,8 +486,8 @@ Section homomorphisms.
   Proof.
     intros. induction X as [|x X IH] using gmultiset_ind; [done|].
     destruct (decide (X = ∅)) as [->|].
-    - by rewrite !big_opMS_union !big_opMS_singleton !big_opMS_empty !right_id.
-    - by rewrite !big_opMS_union !big_opMS_singleton monoid_homomorphism -IH //.
+    - by rewrite !big_opMS_disj_union !big_opMS_singleton !big_opMS_empty !right_id.
+    - by rewrite !big_opMS_disj_union !big_opMS_singleton monoid_homomorphism -IH //.
   Qed.
 
   Context `{!LeibnizEquiv M2}.
diff --git a/theories/algebra/cmra_big_op.v b/theories/algebra/cmra_big_op.v
index 64f5df9f8f32edf39155eb06e1c2181476d5abe9..6bbf5244d71c79146708ff33582370f8234cf1bf 100644
--- a/theories/algebra/cmra_big_op.v
+++ b/theories/algebra/cmra_big_op.v
@@ -31,6 +31,6 @@ Lemma big_opMS_None {M : cmraT} `{Countable A} (f : A → option M) X :
 Proof.
   induction X as [|x X IH] using gmultiset_ind.
   { rewrite big_opMS_empty. set_solver. }
-  rewrite -equiv_None big_opMS_union big_opMS_singleton equiv_None op_None IH.
+  rewrite -equiv_None big_opMS_disj_union big_opMS_singleton equiv_None op_None IH.
   set_solver.
 Qed.
\ No newline at end of file
diff --git a/theories/algebra/gmultiset.v b/theories/algebra/gmultiset.v
index 5fc7d0e4e925af19ac5e3524f2923dbc183aea52..245c6ae9dfad267521daa7e6622ba764942f202e 100644
--- a/theories/algebra/gmultiset.v
+++ b/theories/algebra/gmultiset.v
@@ -13,10 +13,10 @@ Section gmultiset.
   Instance gmultiset_valid : Valid (gmultiset K) := λ _, True.
   Instance gmultiset_validN : ValidN (gmultiset K) := λ _ _, True.
   Instance gmultiset_unit : Unit (gmultiset K) := (∅ : gmultiset K).
-  Instance gmultiset_op : Op (gmultiset K) := union.
+  Instance gmultiset_op : Op (gmultiset K) := disj_union.
   Instance gmultiset_pcore : PCore (gmultiset K) := λ X, Some ∅.
 
-  Lemma gmultiset_op_union X Y : X ⋅ Y = X ∪ Y.
+  Lemma gmultiset_op_disj_union X Y : X ⋅ Y = X ⊎ Y.
   Proof. done. Qed.
   Lemma gmultiset_core_empty X : core X = ∅.
   Proof. done. Qed.
@@ -24,8 +24,8 @@ Section gmultiset.
   Proof.
     split.
     - intros [Z ->%leibniz_equiv].
-      rewrite gmultiset_op_union. apply gmultiset_union_subseteq_l.
-    - intros ->%gmultiset_union_difference. by exists (Y ∖ X).
+      rewrite gmultiset_op_disj_union. apply gmultiset_disj_union_subseteq_l.
+    - intros ->%gmultiset_disj_union_difference. by exists (Y ∖ X).
   Qed.
 
   Lemma gmultiset_ra_mixin : RAMixin (gmultiset K).
@@ -34,8 +34,8 @@ Section gmultiset.
     - by intros X Y Z ->%leibniz_equiv.
     - by intros X Y ->%leibniz_equiv.
     - solve_proper.
-    - intros X1 X2 X3. by rewrite !gmultiset_op_union assoc_L.
-    - intros X1 X2. by rewrite !gmultiset_op_union comm_L.
+    - intros X1 X2 X3. by rewrite !gmultiset_op_disj_union assoc_L.
+    - intros X1 X2. by rewrite !gmultiset_op_disj_union comm_L.
     - intros X. by rewrite gmultiset_core_empty left_id.
     - intros X1 X2 HX. rewrite !gmultiset_core_empty. exists ∅.
       by rewrite left_id.
@@ -47,33 +47,34 @@ Section gmultiset.
   Proof. apply discrete_cmra_discrete. Qed.
 
   Lemma gmultiset_ucmra_mixin : UcmraMixin (gmultiset K).
-  Proof. split. done. intros X. by rewrite gmultiset_op_union left_id_L. done. Qed.
+  Proof. split. done. intros X. by rewrite gmultiset_op_disj_union left_id_L. done. Qed.
   Canonical Structure gmultisetUR := UcmraT (gmultiset K) gmultiset_ucmra_mixin.
 
   Global Instance gmultiset_cancelable X : Cancelable X.
   Proof.
-    apply: discrete_cancelable=> Y Z _ ?. fold_leibniz. by apply (inj (X ∪)).
+    apply: discrete_cancelable=> Y Z _ ?. fold_leibniz. by apply (inj (X ⊎)).
   Qed.
 
-  Lemma gmultiset_opM X mY : X ⋅? mY = X ∪ default ∅ mY.
+  Lemma gmultiset_opM X mY : X ⋅? mY = X ⊎ default ∅ mY.
   Proof. destruct mY; by rewrite /= ?right_id_L. Qed.
 
   Lemma gmultiset_update X Y : X ~~> Y.
   Proof. done. Qed.
 
-  Lemma gmultiset_local_update_alloc X Y X' : (X,Y) ~l~> (X ∪ X', Y ∪ X').
+  Lemma gmultiset_local_update_alloc X Y X' : (X,Y) ~l~> (X ⊎ X', Y ⊎ X').
   Proof.
     rewrite local_update_unital_discrete=> Z' _ /leibniz_equiv_iff->.
-    split. done. rewrite !gmultiset_op_union.
+    split. done. rewrite !gmultiset_op_disj_union.
     by rewrite -!assoc (comm _ Z' X').
   Qed.
 
-  Lemma gmultiset_local_update_dealloc X Y X' : X' ⊆ X → X' ⊆ Y → (X,Y) ~l~> (X ∖ X', Y ∖ X').
+  Lemma gmultiset_local_update_dealloc X Y X' :
+    X' ⊆ X → X' ⊆ Y → (X,Y) ~l~> (X ∖ X', Y ∖ X').
   Proof.
-    intros ->%gmultiset_union_difference ->%gmultiset_union_difference.
+    intros ->%gmultiset_disj_union_difference ->%gmultiset_disj_union_difference.
     rewrite local_update_unital_discrete=> Z' _ /leibniz_equiv_iff->.
-    split. done. rewrite !gmultiset_op_union=> x.
-    repeat (rewrite multiplicity_difference || rewrite multiplicity_union).
+    split. done. rewrite !gmultiset_op_disj_union=> x.
+    repeat (rewrite multiplicity_difference || rewrite multiplicity_disj_union).
     lia.
   Qed.
 End gmultiset.
diff --git a/theories/bi/big_op.v b/theories/bi/big_op.v
index 200b7e8020ea9476b4f125b8d0a3ae0c3500cab0..9bef2299ba5fa1284211faff0253e59584403575 100644
--- a/theories/bi/big_op.v
+++ b/theories/bi/big_op.v
@@ -909,9 +909,9 @@ Section gmultiset.
   Lemma big_sepMS_empty' `{!BiAffine PROP} P Φ : P ⊢ [∗ mset] x ∈ ∅, Φ x.
   Proof. rewrite big_sepMS_empty. apply: affine. Qed.
 
-  Lemma big_sepMS_union Φ X Y :
-    ([∗ mset] y ∈ X ∪ Y, Φ y) ⊣⊢ ([∗ mset] y ∈ X, Φ y) ∗ [∗ mset] y ∈ Y, Φ y.
-  Proof. apply big_opMS_union. Qed.
+  Lemma big_sepMS_disj_union Φ X Y :
+    ([∗ mset] y ∈ X ⊎ Y, Φ y) ⊣⊢ ([∗ mset] y ∈ X, Φ y) ∗ [∗ mset] y ∈ Y, Φ y.
+  Proof. apply big_opMS_disj_union. Qed.
 
   Lemma big_sepMS_delete Φ X x :
     x ∈ X → ([∗ mset] y ∈ X, Φ y) ⊣⊢ Φ x ∗ [∗ mset] y ∈ X ∖ {[ x ]}, Φ y.
diff --git a/theories/proofmode/class_instances_bi.v b/theories/proofmode/class_instances_bi.v
index b4c2bf994098f9e66d4d67c884db37c70f20fe9e..c753f95c9f7ec3aae2b42d17be3bfbdac1808445 100644
--- a/theories/proofmode/class_instances_bi.v
+++ b/theories/proofmode/class_instances_bi.v
@@ -591,10 +591,11 @@ Proof.
   apply wand_elim_l', big_sepL2_app.
 Qed.
 
-Global Instance from_and_big_sepMS_union_persistent `{Countable A} (Φ : A → PROP) X1 X2 :
+Global Instance from_and_big_sepMS_disj_union_persistent
+    `{Countable A} (Φ : A → PROP) X1 X2 :
   (∀ y, Persistent (Φ y)) →
-  FromAnd ([∗ mset] y ∈ X1 ∪ X2, Φ y) ([∗ mset] y ∈ X1, Φ y) ([∗ mset] y ∈ X2, Φ y).
-Proof. intros. by rewrite /FromAnd big_sepMS_union persistent_and_sep_1. Qed.
+  FromAnd ([∗ mset] y ∈ X1 ⊎ X2, Φ y) ([∗ mset] y ∈ X1, Φ y) ([∗ mset] y ∈ X2, Φ y).
+Proof. intros. by rewrite /FromAnd big_sepMS_disj_union persistent_and_sep_1. Qed.
 
 (** FromSep *)
 Global Instance from_sep_sep P1 P2 : FromSep (P1 ∗ P2) P1 P2 | 100.
@@ -649,9 +650,9 @@ Global Instance from_sep_big_sepL2_app {A B} (Φ : nat → A → B → PROP)
     ([∗ list] k ↦ y1;y2 ∈ l1'';l2'', Φ (length l1' + k) y1 y2).
 Proof. rewrite /IsApp=>-> ->. apply wand_elim_l', big_sepL2_app. Qed.
 
-Global Instance from_sep_big_sepMS_union `{Countable A} (Φ : A → PROP) X1 X2 :
-  FromSep ([∗ mset] y ∈ X1 ∪ X2, Φ y) ([∗ mset] y ∈ X1, Φ y) ([∗ mset] y ∈ X2, Φ y).
-Proof. by rewrite /FromSep big_sepMS_union. Qed.
+Global Instance from_sep_big_sepMS_disj_union `{Countable A} (Φ : A → PROP) X1 X2 :
+  FromSep ([∗ mset] y ∈ X1 ⊎ X2, Φ y) ([∗ mset] y ∈ X1, Φ y) ([∗ mset] y ∈ X2, Φ y).
+Proof. by rewrite /FromSep big_sepMS_disj_union. Qed.
 
 Global Instance from_sep_bupd `{BiBUpd PROP} P Q1 Q2 :
   FromSep P Q1 Q2 → FromSep (|==> P) (|==> Q1) (|==> Q2).
@@ -802,9 +803,9 @@ Global Instance into_sep_big_sepL2_cons {A B}
     (Φ 0 x1 x2) ([∗ list] k ↦ y1;y2 ∈ l1';l2', Φ (S k) y1 y2).
 Proof. rewrite /IsCons=>-> ->. by rewrite /IntoSep big_sepL2_cons. Qed.
 
-Global Instance into_sep_big_sepMS_union `{Countable A} (Φ : A → PROP) X1 X2 :
-  IntoSep ([∗ mset] y ∈ X1 ∪ X2, Φ y) ([∗ mset] y ∈ X1, Φ y) ([∗ mset] y ∈ X2, Φ y).
-Proof. by rewrite /IntoSep big_sepMS_union. Qed.
+Global Instance into_sep_big_sepMS_disj_union `{Countable A} (Φ : A → PROP) X1 X2 :
+  IntoSep ([∗ mset] y ∈ X1 ⊎ X2, Φ y) ([∗ mset] y ∈ X1, Φ y) ([∗ mset] y ∈ X2, Φ y).
+Proof. by rewrite /IntoSep big_sepMS_disj_union. Qed.
 
 (** FromOr *)
 Global Instance from_or_or P1 P2 : FromOr (P1 ∨ P2) P1 P2.
diff --git a/theories/proofmode/frame_instances.v b/theories/proofmode/frame_instances.v
index 9a5c852043f724e7caba86485f5c055416f6680e..278bcbf90eada13840fdd961f9bc015bcb0341c0 100644
--- a/theories/proofmode/frame_instances.v
+++ b/theories/proofmode/frame_instances.v
@@ -105,10 +105,10 @@ Global Instance frame_big_sepL2_app {A B} p (Φ : nat → A → B → PROP)
   Frame p R ([∗ list] k ↦ y1;y2 ∈ l1;l2, Φ k y1 y2) Q.
 Proof. rewrite /IsApp /Frame=>-> -> ->. apply wand_elim_l', big_sepL2_app. Qed.
 
-Global Instance frame_big_sepMS_union `{Countable A} p (Φ : A → PROP) R Q X1 X2 :
+Global Instance frame_big_sepMS_disj_union `{Countable A} p (Φ : A → PROP) R Q X1 X2 :
   Frame p R (([∗ mset] y ∈ X1, Φ y) ∗ [∗ mset] y ∈ X2, Φ y) Q →
-  Frame p R ([∗ mset] y ∈ X1 ∪ X2, Φ y) Q.
-Proof. by rewrite /Frame big_sepMS_union. Qed.
+  Frame p R ([∗ mset] y ∈ X1 ⊎ X2, Φ y) Q.
+Proof. by rewrite /Frame big_sepMS_disj_union. Qed.
 
 Global Instance make_and_true_l P : KnownLMakeAnd True P P.
 Proof. apply left_id, _. Qed.