diff --git a/theories/fin_maps.v b/theories/fin_maps.v
index fc357d44bc8b938c3d1c61d512c0565bbbb09e53..447b6751a052cb5e272fea91da58f8d08ef662b6 100644
--- a/theories/fin_maps.v
+++ b/theories/fin_maps.v
@@ -1132,6 +1132,17 @@ Section map_filter.
+ rewrite Eq, Hm, lookup_insert. naive_solver.
+ by rewrite lookup_insert_ne.
Qed.
+ Lemma map_filter_lookup_Some_11 m i x :
+ filter P m !! i = Some x → m !! i = Some x.
+ Proof. apply map_filter_lookup_Some. Qed.
+ Lemma map_filter_lookup_Some_12 m i x :
+ filter P m !! i = Some x → P (i,x).
+ Proof. apply map_filter_lookup_Some. Qed.
+ Lemma map_filter_lookup_Some_2 m i x :
+ m !! i = Some x →
+ P (i, x) →
+ filter P m !! i = Some x.
+ Proof. intros. by apply map_filter_lookup_Some. Qed.
Lemma map_filter_lookup_None m i :
filter P m !! i = None ↔ m !! i = None ∨ ∀ x, m !! i = Some x → ¬ P (i,x).
@@ -1139,6 +1150,14 @@ Section map_filter.
rewrite eq_None_not_Some. unfold is_Some.
setoid_rewrite map_filter_lookup_Some. naive_solver.
Qed.
+ Lemma map_filter_lookup_None_1 m i :
+ filter P m !! i = None →
+ m !! i = None ∨ ∀ x, m !! i = Some x → ¬ P (i,x).
+ Proof. apply map_filter_lookup_None. Qed.
+ Lemma map_filter_lookup_None_2 m i :
+ m !! i = None ∨ (∀ x : A, m !! i = Some x → ¬ P (i, x)) →
+ filter P m !! i = None.
+ Proof. apply map_filter_lookup_None. Qed.
Lemma map_filter_lookup_eq m1 m2 :
(∀ k x, P (k,x) → m1 !! k = Some x ↔ m2 !! k = Some x) →
@@ -1170,6 +1189,14 @@ Section map_filter.
(∀ y, ¬ P (i, y)) → filter P (<[i:=x]> m) = filter P m.
Proof. intros HP. by apply map_filter_insert_not'. Qed.
+ Lemma map_filter_insert_not_delete m i x :
+ ¬ P (i, x) → filter P (<[i:=x]> m) = filter P (delete i m).
+ Proof.
+ intros. rewrite <-insert_delete by done.
+ rewrite map_filter_insert_not'; [done..|].
+ rewrite lookup_delete; done.
+ Qed.
+
Lemma map_filter_delete m i : filter P (delete i m) = delete i (filter P m).
Proof.
apply map_eq. intros j. apply option_eq; intros y.
@@ -1200,6 +1227,24 @@ Section map_filter.
Qed.
End map_filter.
+Lemma map_filter_fmap {A A2} (P : K * A → Prop) `{!∀ x, Decision (P x)}
+ (f : A2 → A) (m : M A2) :
+ filter P (f <$> m) = f <$> filter (λ '(k, v), P (k, (f v))) m.
+Proof.
+ apply map_eq. intros i. apply option_eq; intros x.
+ repeat (rewrite lookup_fmap, fmap_Some || setoid_rewrite map_filter_lookup_Some).
+ naive_solver.
+Qed.
+
+Lemma map_filter_iff {A} (P1 P2 : K * A → Prop)
+ `{!∀ x, Decision (P1 x), !∀ x, Decision (P2 x)} (m : M A) :
+ (∀ x, P1 x ↔ P2 x) →
+ filter P1 m = filter P2 m.
+Proof.
+ intros HPiff. rewrite !map_filter_alt.
+ f_equal. apply list_filter_iff. done.
+Qed.
+
(** ** Properties of the [map_Forall] predicate *)
Section map_Forall.
Context {A} (P : K → A → Prop).
diff --git a/theories/list.v b/theories/list.v
index ed104007b8bf902aa99f94b207206883c202a44c..669c28aab083a3b0eee19ccb5f83cc10de1f78e9 100644
--- a/theories/list.v
+++ b/theories/list.v
@@ -1791,6 +1791,17 @@ Section filter.
Qed.
End filter.
+Lemma list_filter_iff (P1 P2 : A → Prop)
+ `{!∀ x, Decision (P1 x), !∀ x, Decision (P2 x)} (l : list A) :
+ (∀ x, P1 x ↔ P2 x) →
+ filter P1 l = filter P2 l.
+Proof.
+ intros HPiff. induction l as [|a l IH]; [done|].
+ destruct (decide (P1 a)).
+ - rewrite !filter_cons_True by naive_solver. by rewrite IH.
+ - rewrite !filter_cons_False by naive_solver. by rewrite IH.
+Qed.
+
(** ** Properties of the [prefix] and [suffix] predicates *)
Global Instance: PreOrder (@prefix A).
Proof.