diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3db75fa7e336cf73619c03cdebdf4227adaf76e5..edf2268c4a30ab695e80c4593351411d265fbd28 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@ Coq development, but not every API-breaking change is listed.  Changes marked
 
 ## Iris master
 
+**Changes in the theory of Iris itself:**
+
+* [#] Redefine invariants as "semantic invariants" so that they support
+  splitting and other forms of weakening.
+
 **Changes in Coq:**
 
 * A new tactic `iStopProof` to turn the proof mode entailment into an ordinary
diff --git a/theories/base_logic/lib/invariants.v b/theories/base_logic/lib/invariants.v
index 0b6d69a7263531496d2bc29bb6aacb5a92d6f124..6671535a205186d778bdb4308125051db322466c 100644
--- a/theories/base_logic/lib/invariants.v
+++ b/theories/base_logic/lib/invariants.v
@@ -6,123 +6,184 @@ From iris.base_logic.lib Require Import wsat.
 Set Default Proof Using "Type".
 Import uPred.
 
-(** Derived forms and lemmas about them. *)
+(** Semantic Invariants *)
 Definition inv_def `{!invG Î£} (N : namespace) (P : iProp Î£) : iProp Î£ :=
-  (âˆƒ i P', âŒœi âˆˆ (â†‘N:coPset)âŒ âˆ§ â–· â–¡ (P' â†” P) âˆ§ ownI i P')%I.
+  (â–¡ âˆ€ E, âŒœâ†‘N âŠ† EâŒ â†’ |={E,E âˆ– â†‘N}=> â–· P âˆ— (â–· P ={E âˆ– â†‘N,E}=âˆ— True))%I.
 Definition inv_aux : seal (@inv_def). by eexists. Qed.
 Definition inv {Î£ i} := inv_aux.(unseal) Î£ i.
 Definition inv_eq : @inv = @inv_def := inv_aux.(seal_eq).
 Instance: Params (@inv) 3 := {}.
 Typeclasses Opaque inv.
 
+(** * Invariants *)
 Section inv.
-Context `{!invG Î£}.
-Implicit Types i : positive.
-Implicit Types N : namespace.
-Implicit Types P Q R : iProp Î£.
-
-Global Instance inv_contractive N : Contractive (inv N).
-Proof. rewrite inv_eq. solve_contractive. Qed.
-
-Global Instance inv_ne N : NonExpansive (inv N).
-Proof. apply contractive_ne, _. Qed.
-
-Global Instance inv_proper N : Proper ((âŠ£âŠ¢) ==> (âŠ£âŠ¢)) (inv N).
-Proof. apply ne_proper, _. Qed.
-
-Global Instance inv_persistent N P : Persistent (inv N P).
-Proof. rewrite inv_eq /inv; apply _. Qed.
-
-Lemma inv_iff N P Q : â–· â–¡ (P â†” Q) -âˆ— inv N P -âˆ— inv N Q.
-Proof.
-  iIntros "#HPQ". rewrite inv_eq. iDestruct 1 as (i P') "(?&#HP&?)".
-  iExists i, P'. iFrame. iNext; iAlways; iSplit.
-  - iIntros "HP'". iApply "HPQ". by iApply "HP".
-  - iIntros "HQ". iApply "HP". by iApply "HPQ".
-Qed.
-
-Lemma fresh_inv_name (E : gset positive) N : âˆƒ i, i âˆ‰ E âˆ§ i âˆˆ (â†‘N:coPset).
-Proof.
-  exists (coPpick (â†‘ N âˆ– gset_to_coPset E)).
-  rewrite -elem_of_gset_to_coPset (comm and) -elem_of_difference.
-  apply coPpick_elem_of=> Hfin.
-  eapply nclose_infinite, (difference_finite_inv _ _), Hfin.
-  apply gset_to_coPset_finite.
-Qed.
-
-Lemma inv_alloc N E P : â–· P ={E}=âˆ— inv N P.
-Proof.
-  rewrite inv_eq /inv_def uPred_fupd_eq. iIntros "HP [Hw $]".
-  iMod (ownI_alloc (.âˆˆ (â†‘N : coPset)) P with "[$HP $Hw]")
-    as (i ?) "[$ ?]"; auto using fresh_inv_name.
-  do 2 iModIntro. iExists i, P. rewrite -(iff_refl True%I). auto.
-Qed.
-
-Lemma inv_alloc_open N E P :
-  â†‘N âŠ† E â†’ (|={E, Eâˆ–â†‘N}=> inv N P âˆ— (â–·P ={Eâˆ–â†‘N, E}=âˆ— True))%I.
-Proof.
-  rewrite inv_eq /inv_def uPred_fupd_eq. iIntros (Sub) "[Hw HE]".
-  iMod (ownI_alloc_open (.âˆˆ (â†‘N : coPset)) P with "Hw")
-    as (i ?) "(Hw & #Hi & HD)"; auto using fresh_inv_name.
-  iAssert (ownE {[i]} âˆ— ownE (â†‘ N âˆ– {[i]}) âˆ— ownE (E âˆ– â†‘ N))%I
-    with "[HE]" as "(HEi & HEN\i & HE\N)".
-  { rewrite -?ownE_op; [|set_solver..].
-    rewrite assoc_L -!union_difference_L //. set_solver. }
-  do 2 iModIntro. iFrame "HE\N". iSplitL "Hw HEi"; first by iApply "Hw".
-  iSplitL "Hi".
-  { iExists i, P. rewrite -(iff_refl True%I). auto. }
-  iIntros "HP [Hw HE\N]".
-  iDestruct (ownI_close with "[$Hw $Hi $HP $HD]") as "[$ HEi]".
-  do 2 iModIntro. iSplitL; [|done].
-  iCombine "HEi HEN\i HE\N" as "HEN".
-  rewrite -?ownE_op; [|set_solver..].
-  rewrite assoc_L -!union_difference_L //; set_solver.
-Qed.
-
-Lemma inv_open E N P :
-  â†‘N âŠ† E â†’ inv N P ={E,Eâˆ–â†‘N}=âˆ— â–· P âˆ— (â–· P ={Eâˆ–â†‘N,E}=âˆ— True).
-Proof.
-  rewrite inv_eq /inv_def uPred_fupd_eq /uPred_fupd_def.
-  iDestruct 1 as (i P') "(Hi & #HP' & #HiP)".
-  iDestruct "Hi" as % ?%elem_of_subseteq_singleton.
-  rewrite {1 4}(union_difference_L (â†‘ N) E) // ownE_op; last set_solver.
-  rewrite {1 5}(union_difference_L {[ i ]} (â†‘ N)) // ownE_op; last set_solver.
-  iIntros "(Hw & [HE $] & $) !> !>".
-  iDestruct (ownI_open i with "[$Hw $HE $HiP]") as "($ & HP & HD)".
-  iDestruct ("HP'" with "HP") as "$".
-  iIntros "HP [Hw $] !> !>". iApply (ownI_close _ P'). iFrame "HD Hw HiP".
-  iApply "HP'". iFrame.
-Qed.
-
-Lemma inv_open_strong E N P :
-  â†‘N âŠ† E â†’ inv N P ={E,Eâˆ–â†‘N}=âˆ— â–· P âˆ— âˆ€ E', â–· P ={E',â†‘N âˆª E'}=âˆ— True.
-Proof.
-  iIntros (?) "Hinv".
-  iPoseProof (inv_open (â†‘ N) N P with "Hinv") as "H"; first done.
-  rewrite difference_diag_L.
-  iPoseProof (fupd_mask_frame_r _ _ (E âˆ– â†‘ N) with "H") as "H"; first set_solver.
-  rewrite left_id_L -union_difference_L //. iMod "H" as "[$ H]"; iModIntro.
-  iIntros (E') "HP".
-  iPoseProof (fupd_mask_frame_r _ _ E' with "(H HP)") as "H"; first set_solver.
-  by rewrite left_id_L.
-Qed.
-
-Global Instance into_inv_inv N P : IntoInv (inv N P) N := {}.
-
-Global Instance into_acc_inv E N P :
-  IntoAcc (X:=unit) (inv N P) 
-          (â†‘N âŠ† E) True (fupd E (Eâˆ–â†‘N)) (fupd (Eâˆ–â†‘N) E)
-          (Î» _, â–· P)%I (Î» _, â–· P)%I (Î» _, None)%I.
-Proof.
-  rewrite /IntoAcc /accessor exist_unit.
-  iIntros (?) "#Hinv _". iApply inv_open; done.
-Qed.
-
-Lemma inv_open_timeless E N P `{!Timeless P} :
-  â†‘N âŠ† E â†’ inv N P ={E,Eâˆ–â†‘N}=âˆ— P âˆ— (P ={Eâˆ–â†‘N,E}=âˆ— True).
-Proof.
-  iIntros (?) "Hinv". iMod (inv_open with "Hinv") as "[>HP Hclose]"; auto.
-  iIntros "!> {$HP} HP". iApply "Hclose"; auto.
-Qed.
+  Context `{!invG Î£}.
+  Implicit Types i : positive.
+  Implicit Types N : namespace.
+  Implicit Types E : coPset.
+  Implicit Types P Q R : iProp Î£.
+
+  (** ** Internal model of invariants *)
+  Definition own_inv (N : namespace) (P : iProp Î£) : iProp Î£ :=
+    (âˆƒ i P', âŒœi âˆˆ (â†‘N:coPset)âŒ âˆ§ â–· â–¡ (P' â†” P) âˆ§ ownI i P')%I.
+
+  Lemma own_inv_open E N P :
+    â†‘N âŠ† E â†’ own_inv N P ={E,Eâˆ–â†‘N}=âˆ— â–· P âˆ— (â–· P ={Eâˆ–â†‘N,E}=âˆ— True).
+  Proof.
+    rewrite uPred_fupd_eq /uPred_fupd_def.
+    iDestruct 1 as (i P') "(Hi & #HP' & #HiP)".
+    iDestruct "Hi" as % ?%elem_of_subseteq_singleton.
+    rewrite {1 4}(union_difference_L (â†‘ N) E) // ownE_op; last set_solver.
+    rewrite {1 5}(union_difference_L {[ i ]} (â†‘ N)) // ownE_op; last set_solver.
+    iIntros "(Hw & [HE $] & $) !> !>".
+    iDestruct (ownI_open i with "[$Hw $HE $HiP]") as "($ & HP & HD)".
+    iDestruct ("HP'" with "HP") as "$".
+    iIntros "HP [Hw $] !> !>". iApply (ownI_close _ P'). iFrame "HD Hw HiP".
+    iApply "HP'". iFrame.
+  Qed.
+
+  Lemma fresh_inv_name (E : gset positive) N : âˆƒ i, i âˆ‰ E âˆ§ i âˆˆ (â†‘N:coPset).
+  Proof.
+    exists (coPpick (â†‘ N âˆ– gset_to_coPset E)).
+    rewrite -elem_of_gset_to_coPset (comm and) -elem_of_difference.
+    apply coPpick_elem_of=> Hfin.
+    eapply nclose_infinite, (difference_finite_inv _ _), Hfin.
+    apply gset_to_coPset_finite.
+  Qed.
+
+  Lemma own_inv_alloc N E P : â–· P ={E}=âˆ— own_inv N P.
+  Proof.
+    rewrite uPred_fupd_eq. iIntros "HP [Hw $]".
+    iMod (ownI_alloc (.âˆˆ (â†‘N : coPset)) P with "[$HP $Hw]")
+      as (i ?) "[$ ?]"; auto using fresh_inv_name.
+    do 2 iModIntro. iExists i, P. rewrite -(iff_refl True%I). auto.
+  Qed.
+
+  Lemma own_inv_alloc_open N E P :
+    â†‘N âŠ† E â†’ (|={E, Eâˆ–â†‘N}=> own_inv N P âˆ— (â–·P ={Eâˆ–â†‘N, E}=âˆ— True))%I.
+  Proof.
+    rewrite uPred_fupd_eq. iIntros (Sub) "[Hw HE]".
+    iMod (ownI_alloc_open (.âˆˆ (â†‘N : coPset)) P with "Hw")
+      as (i ?) "(Hw & #Hi & HD)"; auto using fresh_inv_name.
+    iAssert (ownE {[i]} âˆ— ownE (â†‘ N âˆ– {[i]}) âˆ— ownE (E âˆ– â†‘ N))%I
+      with "[HE]" as "(HEi & HEN\i & HE\N)".
+    { rewrite -?ownE_op; [|set_solver..].
+      rewrite assoc_L -!union_difference_L //. set_solver. }
+    do 2 iModIntro. iFrame "HE\N". iSplitL "Hw HEi"; first by iApply "Hw".
+    iSplitL "Hi".
+    { iExists i, P. rewrite -(iff_refl True%I). auto. }
+    iIntros "HP [Hw HE\N]".
+    iDestruct (ownI_close with "[$Hw $Hi $HP $HD]") as "[$ HEi]".
+    do 2 iModIntro. iSplitL; [|done].
+    iCombine "HEi HEN\i HE\N" as "HEN".
+    rewrite -?ownE_op; [|set_solver..].
+    rewrite assoc_L -!union_difference_L //; set_solver.
+  Qed.
+
+  Lemma own_inv_to_inv M P: own_inv M P  -âˆ— inv M P.
+  Proof.
+    iIntros "#I". rewrite inv_eq. iIntros (E H).
+    iPoseProof (own_inv_open with "I") as "H"; eauto.
+  Qed.
+
+  (** ** Public API of invariants *)
+  Global Instance inv_contractive N : Contractive (inv N).
+  Proof. rewrite inv_eq. solve_contractive. Qed.
+
+  Global Instance inv_ne N : NonExpansive (inv N).
+  Proof. apply contractive_ne, _. Qed.
+
+  Global Instance inv_proper N : Proper (equiv ==> equiv) (inv N).
+  Proof. apply ne_proper, _. Qed.
+
+  Global Instance inv_persistent N P : Persistent (inv N P).
+  Proof. rewrite inv_eq. apply _. Qed.
+
+  Lemma inv_acc N P Q:
+    inv N P -âˆ— â–· â–¡ (P -âˆ— Q âˆ— (Q -âˆ— P)) -âˆ— inv N Q.
+  Proof.
+    rewrite inv_eq. iIntros "#HI #Acc !>" (E H).
+    iMod ("HI" $! E H) as "[HP Hclose]".
+    iDestruct ("Acc" with "HP") as "[$ HQP]".
+    iIntros "!> HQ". iApply "Hclose". iApply "HQP". done.
+  Qed.
+
+  Lemma inv_iff N P Q : â–· â–¡ (P â†” Q) -âˆ— inv N P -âˆ— inv N Q.
+  Proof.
+    iIntros "#HPQ #HI". iApply (inv_acc with "HI").
+    iIntros "!> !# HP". iSplitL "HP".
+    - by iApply "HPQ".
+    - iIntros "HQ". by iApply "HPQ".
+  Qed.
+
+  Lemma inv_alloc N E P : â–· P ={E}=âˆ— inv N P.
+  Proof.
+    iIntros "HP". iApply own_inv_to_inv.
+    iApply (own_inv_alloc N E with "HP").
+  Qed.
+
+  Lemma inv_alloc_open N E P :
+    â†‘N âŠ† E â†’ (|={E, Eâˆ–â†‘N}=> inv N P âˆ— (â–·P ={Eâˆ–â†‘N, E}=âˆ— True))%I.
+  Proof.
+    iIntros (?). iMod own_inv_alloc_open as "[HI $]"; first done.
+    iApply own_inv_to_inv. done.
+  Qed.
+
+  Lemma inv_open E N P :
+    â†‘N âŠ† E â†’ inv N P ={E,Eâˆ–â†‘N}=âˆ— â–· P âˆ— (â–· P ={Eâˆ–â†‘N,E}=âˆ— True).
+  Proof.
+    rewrite inv_eq /inv_def; iIntros (?) "#HI". by iApply "HI".
+  Qed.
+
+  (** ** Proof mode integration *)
+  Global Instance into_inv_inv N P : IntoInv (inv N P) N := {}.
+
+  Global Instance into_acc_inv N P E:
+    IntoAcc (X := unit) (inv N P)
+            (â†‘N âŠ† E) True (fupd E (E âˆ– â†‘N)) (fupd (E âˆ– â†‘N) E)
+            (Î» _ : (), (â–· P)%I) (Î» _ : (), (â–· P)%I) (Î» _ : (), None).
+  Proof.
+    rewrite inv_eq /IntoAcc /accessor bi.exist_unit.
+    iIntros (?) "#Hinv _". iApply "Hinv"; done.
+  Qed.
+
+  (** ** Derived properties *)
+  Lemma inv_open_strong E N P :
+    â†‘N âŠ† E â†’ inv N P ={E,Eâˆ–â†‘N}=âˆ— â–· P âˆ— âˆ€ E', â–· P ={E',â†‘N âˆª E'}=âˆ— True.
+  Proof.
+    iIntros (?) "Hinv".
+    iPoseProof (inv_open (â†‘ N) N P with "Hinv") as "H"; first done.
+    rewrite difference_diag_L.
+    iPoseProof (fupd_mask_frame_r _ _ (E âˆ– â†‘ N) with "H") as "H"; first set_solver.
+    rewrite left_id_L -union_difference_L //. iMod "H" as "[$ H]"; iModIntro.
+    iIntros (E') "HP".
+    iPoseProof (fupd_mask_frame_r _ _ E' with "(H HP)") as "H"; first set_solver.
+    by rewrite left_id_L.
+  Qed.
+
+  Lemma inv_open_timeless E N P `{!Timeless P} :
+    â†‘N âŠ† E â†’ inv N P ={E,Eâˆ–â†‘N}=âˆ— P âˆ— (P ={Eâˆ–â†‘N,E}=âˆ— True).
+  Proof.
+    iIntros (?) "Hinv". iMod (inv_open with "Hinv") as "[>HP Hclose]"; auto.
+    iIntros "!> {$HP} HP". iApply "Hclose"; auto.
+  Qed.
+
+  Lemma inv_sep_l N P Q : inv N (P âˆ— Q) -âˆ— inv N P.
+  Proof.
+    iIntros "#HI". iApply inv_acc; eauto.
+    iIntros "!> !# [$ $] $".
+  Qed.
+
+  Lemma inv_sep_r N P Q : inv N (P âˆ— Q) -âˆ— inv N Q.
+  Proof.
+    rewrite (comm _ P Q). eapply inv_sep_l.
+  Qed.
+
+  Lemma inv_sep N P Q : inv N (P âˆ— Q) -âˆ— inv N P âˆ— inv N Q.
+  Proof.
+    iIntros "#H".
+    iPoseProof (inv_sep_l with "H") as "$".
+    iPoseProof (inv_sep_r with "H") as "$".
+  Qed.
 
 End inv.