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(* Copyright (c) 2012-2013, Robbert Krebbers. *)
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(* This file is distributed under the terms of the BSD license. *)
(** Finite maps associate data to keys. This file defines an interface for
finite maps and collects some theory on it. Most importantly, it proves useful
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induction principles for finite maps and implements the tactic
[simplify_map_equality] to simplify goals involving finite maps. *)
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Require Import Permutation.
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Require Export ars vector orders.

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(** * Axiomatization of finite maps *)
(** We require Leibniz equality to be extensional on finite maps. This of
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course limits the space of finite map implementations, but since we are mainly
interested in finite maps with numbers as indexes, we do not consider this to
be a serious limitation. The main application of finite maps is to implement
the memory, where extensionality of Leibniz equality is very important for a
convenient use in the assertions of our axiomatic semantics. *)
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(** Finiteness is axiomatized by requiring that each map can be translated
to an association list. The translation to association lists is used to
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prove well founded recursion on finite maps. *)
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(** Finite map implementations are required to implement the [merge] function
which enables us to give a generic implementation of [union_with],
[intersection_with], and [difference_with]. *)
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Class FinMapToList K A M := map_to_list: M  list (K * A).
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Class FinMap K M `{!FMap M}
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    `{ A, Lookup K A (M A)} `{ A, Empty (M A)} `{ A, PartialAlter K A (M A)}
    `{!Merge M} `{ A, FinMapToList K A (M A)}
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    `{ i j : K, Decision (i = j)} := {
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  map_eq {A} (m1 m2 : M A) : ( i, m1 !! i = m2 !! i)  m1 = m2;
  lookup_empty {A} i : ( : M A) !! i = None;
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  lookup_partial_alter {A} f (m : M A) i :
    partial_alter f i m !! i = f (m !! i);
  lookup_partial_alter_ne {A} f (m : M A) i j :
    i  j  partial_alter f i m !! j = m !! j;
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  lookup_fmap {A B} (f : A  B) (m : M A) i : (f <$> m) !! i = f <$> m !! i;
  map_to_list_nodup {A} (m : M A) : NoDup (map_to_list m);
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  elem_of_map_to_list {A} (m : M A) i x :
    (i,x)  map_to_list m  m !! i = Some x;
  lookup_merge {A B C} (f : option A  option B  option C)
      `{!PropHolds (f None None = None)} m1 m2 i :
    merge f m1 m2 !! i = f (m1 !! i) (m2 !! i)
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}.

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(** * Derived operations *)
(** All of the following functions are defined in a generic way for arbitrary
finite map implementations. These generic implementations do not cause a
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significant performance loss to make including them in the finite map interface
worthwhile. *)
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Instance map_insert `{PartialAlter K A M} : Insert K A M :=
  λ i x, partial_alter (λ _, Some x) i.
Instance map_alter `{PartialAlter K A M} : Alter K A M :=
  λ f, partial_alter (fmap f).
Instance map_delete `{PartialAlter K A M} : Delete K M :=
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  partial_alter (λ _, None).
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Instance map_singleton `{PartialAlter K A M}
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  `{Empty M} : Singleton (K * A) M := λ p, <[fst p:=snd p]>.
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Definition map_of_list `{Insert K A M} `{Empty M}
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  (l : list (K * A)) : M := insert_list l .
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Instance map_union_with `{Merge M} {A} : UnionWith A (M A) :=
  λ f, merge (union_with f).
Instance map_intersection_with `{Merge M} {A} : IntersectionWith A (M A) :=
  λ f, merge (intersection_with f).
Instance map_difference_with `{Merge M} {A} : DifferenceWith A (M A) :=
  λ f, merge (difference_with f).
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(** The relation [intersection_forall R] on finite maps describes that the
relation [R] holds for each pair in the intersection. *)
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Definition map_forall `{Lookup K A M} (P : K  A  Prop) : M  Prop :=
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  λ m,  i x, m !! i = Some x  P i x.
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Definition map_intersection_forall `{Lookup K A M}
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    (R : relation A) : relation M := λ m1 m2,
   i x1 x2, m1 !! i = Some x1  m2 !! i = Some x2  R x1 x2.
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Instance map_disjoint `{ A, Lookup K A (M A)} : Disjoint (M A) :=
  λ A, map_intersection_forall (λ _ _, False).
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(** The union of two finite maps only has a meaningful definition for maps
that are disjoint. However, as working with partial functions is inconvenient
in Coq, we define the union as a total function. In case both finite maps
have a value at the same index, we take the value of the first map. *)
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Instance map_union `{Merge M} {A} : Union (M A) := union_with (λ x _, Some x).
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Instance map_intersection `{Merge M} {A} : Intersection (M A) :=
  intersection_with (λ x _, Some x).

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(** The difference operation removes all values from the first map whose
index contains a value in the second map as well. *)
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Instance map_difference `{Merge M} {A} : Difference (M A) :=
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  difference_with (λ _ _, None).
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(** * Theorems *)
Section theorems.
Context `{FinMap K M}.

Global Instance map_subseteq {A} : SubsetEq (M A) := λ m1 m2,
   i x, m1 !! i = Some x  m2 !! i = Some x.
Global Instance: BoundedPreOrder (M A).
Proof. split; [firstorder |]. intros m i x. by rewrite lookup_empty. Qed.
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Global Instance : PartialOrder (@subseteq (M A) _).
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Proof.
  split; [apply _ |].
  intros ????. apply map_eq. intros i. apply option_eq. naive_solver.
Qed.

Lemma lookup_weaken {A} (m1 m2 : M A) i x :
  m1 !! i = Some x  m1  m2  m2 !! i = Some x.
Proof. auto. Qed.
Lemma lookup_weaken_is_Some {A} (m1 m2 : M A) i :
  is_Some (m1 !! i)  m1  m2  is_Some (m2 !! i).
Proof. inversion 1. eauto using lookup_weaken. Qed.
Lemma lookup_weaken_None {A} (m1 m2 : M A) i :
  m2 !! i = None  m1  m2  m1 !! i = None.
Proof.
  rewrite eq_None_not_Some. intros Hm2 Hm1m2.
  specialize (Hm1m2 i). destruct (m1 !! i); naive_solver.
Qed.

Lemma lookup_weaken_inv {A} (m1 m2 : M A) i x y :
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  m1 !! i = Some x  m1  m2  m2 !! i = Some y  x = y.
Proof. intros Hm1 ? Hm2. eapply lookup_weaken in Hm1; eauto. congruence. Qed.
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Lemma lookup_ne {A} (m : M A) i j : m !! i  m !! j  i  j.
Proof. congruence. Qed.
Lemma map_empty {A} (m : M A) : ( i, m !! i = None)  m = .
Proof. intros Hm. apply map_eq. intros. by rewrite Hm, lookup_empty. Qed.
Lemma lookup_empty_is_Some {A} i : ¬is_Some (( : M A) !! i).
Proof. rewrite lookup_empty. by inversion 1. Qed.
Lemma lookup_empty_Some {A} i (x : A) : ¬ !! i = Some x.
Proof. by rewrite lookup_empty. Qed.

Lemma map_subset_empty {A} (m : M A) : m  .
Proof. intros [? []]. intros i x. by rewrite lookup_empty. Qed.

(** ** Properties of the [partial_alter] operation *)
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Lemma partial_alter_ext {A} (f g : option A  option A) (m : M A) i :
  ( x, m !! i = x  f x = g x)  partial_alter f i m = partial_alter g i m.
Proof.
  intros Hfg. apply map_eq. intros j. destruct (decide (i = j)); subst.
  * rewrite !lookup_partial_alter. by apply Hfg.
  * by rewrite !lookup_partial_alter_ne.
Qed.
Lemma partial_alter_compose {A} f g (m : M A) i:
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  partial_alter (f  g) i m = partial_alter f i (partial_alter g i m).
Proof.
  intros. apply map_eq. intros ii. case (decide (i = ii)).
  * intros. subst. by rewrite !lookup_partial_alter.
  * intros. by rewrite !lookup_partial_alter_ne.
Qed.
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Lemma partial_alter_commute {A} f g (m : M A) i j :
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  i  j  partial_alter f i (partial_alter g j m) =
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    partial_alter g j (partial_alter f i m).
Proof.
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  intros. apply map_eq. intros jj. destruct (decide (jj = j)).
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  * subst. by rewrite lookup_partial_alter_ne,
      !lookup_partial_alter, lookup_partial_alter_ne.
  * destruct (decide (jj = i)).
    + subst. by rewrite lookup_partial_alter,
       !lookup_partial_alter_ne, lookup_partial_alter by congruence.
    + by rewrite !lookup_partial_alter_ne by congruence.
Qed.
Lemma partial_alter_self_alt {A} (m : M A) i x :
  x = m !! i  partial_alter (λ _, x) i m = m.
Proof.
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  intros. apply map_eq. intros ii. destruct (decide (i = ii)).
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  * subst. by rewrite lookup_partial_alter.
  * by rewrite lookup_partial_alter_ne.
Qed.
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Lemma partial_alter_self {A} (m : M A) i : partial_alter (λ _, m !! i) i m = m.
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Proof. by apply partial_alter_self_alt. Qed.

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Lemma partial_alter_subseteq {A} f (m : M A) i :
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  m !! i = None  m  partial_alter f i m.
Proof. intros Hi j x Hj. rewrite lookup_partial_alter_ne; congruence. Qed.
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Lemma partial_alter_subset {A} f (m : M A) i :
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  m !! i = None  is_Some (f (m !! i))  m  partial_alter f i m.
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Proof.
  intros Hi Hfi. split.
  * by apply partial_alter_subseteq.
  * inversion Hfi as [x Hx]. intros Hm.
    apply (Some_ne_None x). rewrite <-(Hm i x); [done|].
    by rewrite lookup_partial_alter.
Qed.

(** ** Properties of the [alter] operation *)
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Lemma alter_ext {A} (f g : A  A) (m : M A) i :
  ( x, m !! i = Some x  f x = g x)  alter f i m = alter g i m.
Proof. intro. apply partial_alter_ext. intros [x|] ?; simpl; f_equal; auto. Qed.

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Lemma lookup_alter {A} (f : A  A) m i : alter f i m !! i = f <$> m !! i.
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Proof. apply lookup_partial_alter. Qed.
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Lemma lookup_alter_ne {A} (f : A  A) m i j : i  j  alter f i m !! j = m !! j.
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Proof. apply lookup_partial_alter_ne. Qed.

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Lemma alter_compose {A} (f g : A  A) (m : M A) i:
  alter (f  g) i m = alter f i (alter g i m).
Proof.
  unfold alter, map_alter. rewrite <-partial_alter_compose.
  apply partial_alter_ext. by intros [?|].
Qed.

Lemma alter_commute {A} (f g : A  A) (m : M A) i j :
  i  j  alter f i (alter g j m) = alter g j (alter f i m).
Proof. apply partial_alter_commute. Qed.

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Lemma lookup_alter_Some {A} (f : A  A) m i j y :
  alter f i m !! j = Some y 
    (i = j   x, m !! j = Some x  y = f x)  (i  j  m !! j = Some y).
Proof.
  destruct (decide (i = j)); subst.
  * rewrite lookup_alter. naive_solver (simplify_option_equality; eauto).
  * rewrite lookup_alter_ne by done. naive_solver.
Qed.
Lemma lookup_alter_None {A} (f : A  A) m i j :
  alter f i m !! j = None  m !! j = None.
Proof.
  destruct (decide (i = j)); subst.
  * by rewrite lookup_alter, fmap_None.
  * by rewrite lookup_alter_ne.
Qed.

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Lemma alter_None {A} (f : A  A) m i : m !! i = None  alter f i m = m.
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Proof.
  intros Hi. apply map_eq. intros j. destruct (decide (i = j)); subst.
  * by rewrite lookup_alter, !Hi.
  * by rewrite lookup_alter_ne.
Qed.

(** ** Properties of the [delete] operation *)
Lemma lookup_delete {A} (m : M A) i : delete i m !! i = None.
Proof. apply lookup_partial_alter. Qed.
Lemma lookup_delete_ne {A} (m : M A) i j : i  j  delete i m !! j = m !! j.
Proof. apply lookup_partial_alter_ne. Qed.

Lemma lookup_delete_Some {A} (m : M A) i j y :
  delete i m !! j = Some y  i  j  m !! j = Some y.
Proof.
  split.
  * destruct (decide (i = j)); subst;
      rewrite ?lookup_delete, ?lookup_delete_ne; intuition congruence.
  * intros [??]. by rewrite lookup_delete_ne.
Qed.
Lemma lookup_delete_None {A} (m : M A) i j :
  delete i m !! j = None  i = j  m !! j = None.
Proof.
  destruct (decide (i = j)).
  * subst. rewrite lookup_delete. tauto.
  * rewrite lookup_delete_ne; tauto.
Qed.

Lemma delete_empty {A} i : delete i ( : M A) = .
Proof. rewrite <-(partial_alter_self ) at 2. by rewrite lookup_empty. Qed.
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Lemma delete_singleton {A} i (x : A) : delete i {[i, x]} = .
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Proof. setoid_rewrite <-partial_alter_compose. apply delete_empty. Qed.
Lemma delete_commute {A} (m : M A) i j :
  delete i (delete j m) = delete j (delete i m).
Proof. destruct (decide (i = j)). by subst. by apply partial_alter_commute. Qed.
Lemma delete_insert_ne {A} (m : M A) i j x :
  i  j  delete i (<[j:=x]>m) = <[j:=x]>(delete i m).
Proof. intro. by apply partial_alter_commute. Qed.

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Lemma delete_notin {A} (m : M A) i : m !! i = None  delete i m = m.
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Proof.
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  intros. apply map_eq. intros j. destruct (decide (i = j)).
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  * subst. by rewrite lookup_delete.
  * by apply lookup_delete_ne.
Qed.

Lemma delete_partial_alter {A} (m : M A) i f :
  m !! i = None  delete i (partial_alter f i m) = m.
Proof.
  intros. unfold delete, map_delete. rewrite <-partial_alter_compose.
  unfold compose. by apply partial_alter_self_alt.
Qed.
Lemma delete_insert {A} (m : M A) i x :
  m !! i = None  delete i (<[i:=x]>m) = m.
Proof. apply delete_partial_alter. Qed.
Lemma insert_delete {A} (m : M A) i x :
  m !! i = Some x  <[i:=x]>(delete i m) = m.
Proof.
  intros Hmi. unfold delete, map_delete, insert, map_insert.
  rewrite <-partial_alter_compose. unfold compose. rewrite <-Hmi.
  by apply partial_alter_self_alt.
Qed.

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Lemma delete_subseteq {A} (m : M A) i : delete i m  m.
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Proof. intros j x. rewrite lookup_delete_Some. tauto. Qed.
Lemma delete_subseteq_compat {A} (m1 m2 : M A) i :
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  m1  m2  delete i m1  delete i m2.
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Proof. intros ? j x. rewrite !lookup_delete_Some. intuition eauto. Qed.
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Lemma delete_subset_alt {A} (m : M A) i x : m !! i = Some x  delete i m  m.
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Proof.
  split.
  * apply delete_subseteq.
  * intros Hi. apply (None_ne_Some x).
    by rewrite <-(lookup_delete m i), (Hi i x).
Qed.
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Lemma delete_subset {A} (m : M A) i : is_Some (m !! i)  delete i m  m.
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Proof. inversion 1. eauto using delete_subset_alt. Qed.

(** ** Properties of the [insert] operation *)
Lemma lookup_insert {A} (m : M A) i x : <[i:=x]>m !! i = Some x.
Proof. unfold insert. apply lookup_partial_alter. Qed.
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Lemma lookup_insert_rev {A}  (m : M A) i x y : <[i:=x]>m !! i = Some y  x = y.
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Proof. rewrite lookup_insert. congruence. Qed.
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Lemma lookup_insert_ne {A} (m : M A) i j x : i  j  <[i:=x]>m !! j = m !! j.
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Proof. unfold insert. apply lookup_partial_alter_ne. Qed.
Lemma insert_commute {A} (m : M A) i j x y :
  i  j  <[i:=x]>(<[j:=y]>m) = <[j:=y]>(<[i:=x]>m).
Proof. apply partial_alter_commute. Qed.

Lemma lookup_insert_Some {A} (m : M A) i j x y :
  <[i:=x]>m !! j = Some y  (i = j  x = y)  (i  j  m !! j = Some y).
Proof.
  split.
  * destruct (decide (i = j)); subst;
      rewrite ?lookup_insert, ?lookup_insert_ne; intuition congruence.
  * intros [[??]|[??]].
    + subst. apply lookup_insert.
    + by rewrite lookup_insert_ne.
Qed.
Lemma lookup_insert_None {A} (m : M A) i j x :
  <[i:=x]>m !! j = None  m !! j = None  i  j.
Proof.
  split.
  * destruct (decide (i = j)); subst;
      rewrite ?lookup_insert, ?lookup_insert_ne; intuition congruence.
  * intros [??]. by rewrite lookup_insert_ne.
Qed.

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Lemma insert_subseteq {A} (m : M A) i x : m !! i = None  m  <[i:=x]>m.
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Proof. apply partial_alter_subseteq. Qed.
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Lemma insert_subset {A} (m : M A) i x : m !! i = None  m  <[i:=x]>m.
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Proof. intro. apply partial_alter_subset; eauto. Qed.
Lemma insert_subseteq_r {A} (m1 m2 : M A) i x :
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  m1 !! i = None  m1  m2  m1  <[i:=x]>m2.
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Proof.
  intros ?? j ?. destruct (decide (j = i)); subst.
  * congruence.
  * rewrite lookup_insert_ne; auto.
Qed.

Lemma insert_delete_subseteq {A} (m1 m2 : M A) i x :
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  m1 !! i = None  <[i:=x]> m1  m2  m1  delete i m2.
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Proof.
  intros Hi Hix j y Hj. destruct (decide (i = j)); subst.
  * congruence.
  * rewrite lookup_delete_ne by done. apply Hix.
    by rewrite lookup_insert_ne by done.
Qed.
Lemma delete_insert_subseteq {A} (m1 m2 : M A) i x :
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  m1 !! i = Some x  delete i m1  m2  m1  <[i:=x]> m2.
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Proof.
  intros Hix Hi j y Hj. destruct (decide (i = j)); subst.
  * rewrite lookup_insert. congruence.
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  * rewrite lookup_insert_ne by done. apply Hi. by rewrite lookup_delete_ne.
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Qed.

Lemma insert_delete_subset {A} (m1 m2 : M A) i x :
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  m1 !! i = None  <[i:=x]> m1  m2  m1  delete i m2.
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Proof.
  intros ? [Hm12 Hm21]. split.
  * eauto using insert_delete_subseteq.
  * contradict Hm21. apply delete_insert_subseteq; auto.
    apply Hm12. by rewrite lookup_insert.
Qed.

Lemma insert_subset_inv {A} (m1 m2 : M A) i x :
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  m1 !! i = None  <[i:=x]> m1  m2 
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   m2', m2 = <[i:=x]>m2'  m1  m2'  m2' !! i = None.
Proof.
  intros Hi Hm1m2. exists (delete i m2). split_ands.
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  * rewrite insert_delete. done. eapply lookup_weaken, strict_include; eauto.
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    by rewrite lookup_insert.
  * eauto using insert_delete_subset.
  * by rewrite lookup_delete.
Qed.

(** ** Properties of the singleton maps *)
Lemma lookup_singleton_Some {A} i j (x y : A) :
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  {[i, x]} !! j = Some y  i = j  x = y.
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Proof.
  unfold singleton, map_singleton.
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  rewrite lookup_insert_Some, lookup_empty. simpl. intuition congruence.
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Qed.
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Lemma lookup_singleton_None {A} i j (x : A) : {[i, x]} !! j = None  i  j.
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Proof.
  unfold singleton, map_singleton.
  rewrite lookup_insert_None, lookup_empty. simpl. tauto.
Qed.
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Lemma lookup_singleton {A} i (x : A) : {[i, x]} !! i = Some x.
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Proof. by rewrite lookup_singleton_Some. Qed.
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Lemma lookup_singleton_ne {A} i j (x : A) : i  j  {[i, x]} !! j = None.
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Proof. by rewrite lookup_singleton_None. Qed.

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Lemma insert_singleton {A} i (x y : A) : <[i:=y]>{[i, x]} = {[i, y]}.
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Proof.
  unfold singleton, map_singleton, insert, map_insert.
  by rewrite <-partial_alter_compose.
Qed.
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Lemma alter_singleton {A} (f : A  A) i x : alter f i {[i,x]} = {[i, f x]}.
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Proof.
  intros. apply map_eq. intros i'. destruct (decide (i = i')); subst.
  * by rewrite lookup_alter, !lookup_singleton.
  * by rewrite lookup_alter_ne, !lookup_singleton_ne.
Qed.
Lemma alter_singleton_ne {A} (f : A  A) i j x :
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  i  j  alter f i {[j,x]} = {[j,x]}.
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Proof.
  intros. apply map_eq. intros i'. destruct (decide (i = i')); subst.
  * by rewrite lookup_alter, lookup_singleton_ne.
  * by rewrite lookup_alter_ne.
Qed.

(** ** Properties of conversion to lists *)
Lemma map_to_list_unique {A} (m : M A) i x y :
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  (i,x)  map_to_list m  (i,y)  map_to_list m  x = y.
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Proof. rewrite !elem_of_map_to_list. congruence. Qed.
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Lemma map_to_list_key_nodup {A} (m : M A) : NoDup (fst <$> map_to_list m).
Proof. eauto using NoDup_fmap_fst, map_to_list_unique, map_to_list_nodup. Qed.
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Lemma elem_of_map_of_list_1 {A} (l : list (K * A)) i x :
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  NoDup (fst <$> l)  (i,x)  l  map_of_list l !! i = Some x.
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Proof.
  induction l as [|[j y] l IH]; simpl.
  { by rewrite elem_of_nil. }
  rewrite NoDup_cons, elem_of_cons, elem_of_list_fmap.
  intros [Hl ?] [?|?]; simplify_equality.
  { by rewrite lookup_insert. }
  destruct (decide (i = j)); simplify_equality.
  * destruct Hl. by exists (j,x).
  * rewrite lookup_insert_ne; auto.
Qed.
Lemma elem_of_map_of_list_2 {A} (l : list (K * A)) i x :
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  map_of_list l !! i = Some x  (i,x)  l.
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Proof.
  induction l as [|[j y] l IH]; simpl.
  { by rewrite lookup_empty. }
  rewrite elem_of_cons. destruct (decide (i = j)); simplify_equality.
  * rewrite lookup_insert; intuition congruence.
  * rewrite lookup_insert_ne; intuition congruence.
Qed.
Lemma elem_of_map_of_list {A} (l : list (K * A)) i x :
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  NoDup (fst <$> l)  (i,x)  l  map_of_list l !! i = Some x.
Proof. split; auto using elem_of_map_of_list_1, elem_of_map_of_list_2. Qed.
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Lemma not_elem_of_map_of_list_1 {A} (l : list (K * A)) i :
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  i  fst <$> l  map_of_list l !! i = None.
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Proof.
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  rewrite elem_of_list_fmap, eq_None_not_Some.
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  intros Hi [x ?]. destruct Hi. exists (i,x). simpl.
  auto using elem_of_map_of_list_2.
Qed.
Lemma not_elem_of_map_of_list_2 {A} (l : list (K * A)) i :
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  map_of_list l !! i = None  i  fst <$> l.
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Proof.
  induction l as [|[j y] l IH]; simpl.
  { rewrite elem_of_nil. tauto. }
  rewrite elem_of_cons. destruct (decide (i = j)); simplify_equality.
  * by rewrite lookup_insert.
  * by rewrite lookup_insert_ne; intuition.
Qed.
Lemma not_elem_of_map_of_list {A} (l : list (K * A)) i :
  i  fst <$> l  map_of_list l !! i = None.
Proof.
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  split; auto using not_elem_of_map_of_list_1, not_elem_of_map_of_list_2.
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Qed.

Lemma map_of_list_proper {A} (l1 l2 : list (K * A)) :
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  NoDup (fst <$> l1)  l1  l2  map_of_list l1 = map_of_list l2.
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Proof.
  intros ? Hperm. apply map_eq. intros i. apply option_eq. intros x.
  by rewrite <-!elem_of_map_of_list; rewrite <-?Hperm.
Qed.
Lemma map_of_list_inj {A} (l1 l2 : list (K * A)) :
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  NoDup (fst <$> l1)  NoDup (fst <$> l2) 
  map_of_list l1 = map_of_list l2  l1  l2.
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Proof.
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  intros ?? Hl1l2. apply NoDup_Permutation; auto using (fmap_nodup_1 fst).
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  intros [i x]. by rewrite !elem_of_map_of_list, Hl1l2.
Qed.
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Lemma map_of_to_list {A} (m : M A) : map_of_list (map_to_list m) = m.
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Proof.
  apply map_eq. intros i. apply option_eq. intros x.
  by rewrite <-elem_of_map_of_list, elem_of_map_to_list
    by auto using map_to_list_key_nodup.
Qed.
Lemma map_to_of_list {A} (l : list (K * A)) :
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  NoDup (fst <$> l)  map_to_list (map_of_list l)  l.
Proof. auto using map_of_list_inj, map_to_list_key_nodup, map_of_to_list. Qed.
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Lemma map_to_list_inj {A} (m1 m2 : M A) :
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  map_to_list m1  map_to_list m2  m1 = m2.
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Proof.
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  intros. rewrite <-(map_of_to_list m1), <-(map_of_to_list m2).
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  auto using map_of_list_proper, map_to_list_key_nodup.
Qed.

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Lemma map_to_list_empty {A} : map_to_list  = @nil (K * A).
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Proof.
  apply elem_of_nil_inv. intros [i x].
  rewrite elem_of_map_to_list. apply lookup_empty_Some.
Qed.
Lemma map_to_list_insert {A} (m : M A) i x :
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  m !! i = None  map_to_list (<[i:=x]>m)  (i,x) :: map_to_list m.
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Proof.
  intros. apply map_of_list_inj; simpl.
  * apply map_to_list_key_nodup.
  * constructor; auto using map_to_list_key_nodup.
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    rewrite elem_of_list_fmap. intros [[??] [? Hlookup]]; subst; simpl in *.
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    rewrite elem_of_map_to_list in Hlookup. congruence.
  * by rewrite !map_of_to_list.
Qed.

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Lemma map_of_list_nil {A} : map_of_list (@nil (K * A)) = .
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Proof. done. Qed.
Lemma map_of_list_cons {A} (l : list (K * A)) i x :
  map_of_list ((i, x) :: l) = <[i:=x]>(map_of_list l).
Proof. done. Qed.

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Lemma map_to_list_empty_inv_alt {A}  (m : M A) : map_to_list m  []  m = .
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Proof. rewrite <-map_to_list_empty. apply map_to_list_inj. Qed.
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Lemma map_to_list_empty_inv {A} (m : M A) : map_to_list m = []  m = .
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Proof. intros Hm. apply map_to_list_empty_inv_alt. by rewrite Hm. Qed.

Lemma map_to_list_insert_inv {A} (m : M A) l i x :
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  map_to_list m  (i,x) :: l  m = <[i:=x]>(map_of_list l).
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Proof.
  intros Hperm. apply map_to_list_inj.
  assert (NoDup (fst <$> (i, x) :: l)) as Hnodup.
  { rewrite <-Hperm. auto using map_to_list_key_nodup. }
  simpl in Hnodup. rewrite NoDup_cons in Hnodup. destruct Hnodup.
  rewrite Hperm, map_to_list_insert, map_to_of_list;
    auto using not_elem_of_map_of_list_1.
Qed.

(** * Induction principles *)
Lemma map_ind {A} (P : M A  Prop) :
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  P   ( i x m, m !! i = None  P m  P (<[i:=x]>m))   m, P m.
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Proof.
  intros Hemp Hins.
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  cut ( l, NoDup (fst <$> l)   m, map_to_list m  l  P m).
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  { intros help m.
    apply (help (map_to_list m)); auto using map_to_list_key_nodup. }
  induction l as [|[i x] l IH]; intros Hnodup m Hml.
  { apply map_to_list_empty_inv_alt in Hml. by subst. }
  inversion_clear Hnodup.
  apply map_to_list_insert_inv in Hml. subst. apply Hins.
  * by apply not_elem_of_map_of_list_1.
  * apply IH; auto using map_to_of_list.
Qed.

Lemma map_to_list_length {A} (m1 m2 : M A) :
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  m1  m2  length (map_to_list m1) < length (map_to_list m2).
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Proof.
  revert m2. induction m1 as [|i x m ? IH] using map_ind.
  { intros m2 Hm2. rewrite map_to_list_empty. simpl.
    apply neq_0_lt. intros Hlen. symmetry in Hlen.
    apply nil_length, map_to_list_empty_inv in Hlen.
    rewrite Hlen in Hm2. destruct (irreflexivity ()  Hm2). }
  intros m2 Hm2.
  destruct (insert_subset_inv m m2 i x) as (m2'&?&?&?); auto; subst.
  rewrite !map_to_list_insert; simpl; auto with arith.
Qed.

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Lemma map_wf {A} : wf (strict (@subseteq (M A) _)).
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Proof.
  apply (wf_projected (<) (length  map_to_list)).
  * by apply map_to_list_length.
  * by apply lt_wf.
Qed.

(** ** Properties of the [map_forall] predicate *)
Section map_forall.
Context {A} (P : K  A  Prop).

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Lemma map_forall_to_list m : map_forall P m  Forall (curry P) (map_to_list m).
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Proof.
  rewrite Forall_forall. split.
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  * intros Hforall [i x]. rewrite elem_of_map_to_list. by apply (Hforall i x).
  * intros Hforall i x. rewrite <-elem_of_map_to_list. by apply (Hforall (i,x)).
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Qed.

Context `{ i x, Decision (P i x)}.
Global Instance map_forall_dec m : Decision (map_forall P m).
Proof.
  refine (cast_if (decide (Forall (curry P) (map_to_list m))));
    by rewrite map_forall_to_list.
Defined.

Lemma map_not_forall (m : M A) :
  ¬map_forall P m   i x, m !! i = Some x  ¬P i x.
Proof.
  split.
  * rewrite map_forall_to_list. intros Hm.
    apply (not_Forall_Exists _), Exists_exists in Hm.
    destruct Hm as ([i x]&?&?). exists i x. by rewrite <-elem_of_map_to_list.
  * intros (i&x&?&?) Hm. specialize (Hm i x). tauto.
Qed.
End map_forall.

(** ** Properties of the [merge] operation *)
Lemma merge_Some {A B C} (f : option A  option B  option C)
    `{!PropHolds (f None None = None)} m1 m2 m :
  ( i, m !! i = f (m1 !! i) (m2 !! i))  merge f m1 m2 = m.
Proof.
  split; [| intro; subst; apply (lookup_merge _) ].
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  intros Hlookup. apply map_eq. intros. rewrite Hlookup. apply (lookup_merge _).
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Qed.

Section merge.
Context {A} (f : option A  option A  option A).

Global Instance: LeftId (=) None f  LeftId (=)  (merge f).
Proof.
  intros ??. apply map_eq. intros.
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  by rewrite !(lookup_merge f), lookup_empty, (left_id_L None f).
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Qed.
Global Instance: RightId (=) None f  RightId (=)  (merge f).
Proof.
  intros ??. apply map_eq. intros.
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  by rewrite !(lookup_merge f), lookup_empty, (right_id_L None f).
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Qed.

Context `{!PropHolds (f None None = None)}.

Lemma merge_commutative m1 m2 :
  ( i, f (m1 !! i) (m2 !! i) = f (m2 !! i) (m1 !! i)) 
  merge f m1 m2 = merge f m2 m1.
Proof. intros. apply map_eq. intros. by rewrite !(lookup_merge f). Qed.
Global Instance: Commutative (=) f  Commutative (=) (merge f).
Proof.
  intros ???. apply merge_commutative. intros. by apply (commutative f).
Qed.
Lemma merge_associative m1 m2 m3 :
  ( i, f (m1 !! i) (f (m2 !! i) (m3 !! i)) =
        f (f (m1 !! i) (m2 !! i)) (m3 !! i)) 
  merge f m1 (merge f m2 m3) = merge f (merge f m1 m2) m3.
Proof. intros. apply map_eq. intros. by rewrite !(lookup_merge f). Qed.
Global Instance: Associative (=) f  Associative (=) (merge f).
Proof.
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  intros ????. apply merge_associative. intros. by apply (associative_L f).
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Qed.
Lemma merge_idempotent m1 :
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  ( i, f (m1 !! i) (m1 !! i) = m1 !! i)  merge f m1 m1 = m1.
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Proof. intros. apply map_eq. intros. by rewrite !(lookup_merge f). Qed.
Global Instance: Idempotent (=) f  Idempotent (=) (merge f).
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Proof. intros ??. apply merge_idempotent. intros. by apply (idempotent f). Qed.
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Lemma partial_alter_merge (g g1 g2 : option A  option A) m1 m2 i :
  g (f (m1 !! i) (m2 !! i)) = f (g1 (m1 !! i)) (g2 (m2 !! i)) 
  partial_alter g i (merge f m1 m2) =
    merge f (partial_alter g1 i m1) (partial_alter g2 i m2).
Proof.
  intro. apply map_eq. intros j. destruct (decide (i = j)); subst.
  * by rewrite (lookup_merge _), !lookup_partial_alter, !(lookup_merge _).
  * by rewrite (lookup_merge _), !lookup_partial_alter_ne, (lookup_merge _).
Qed.
Lemma partial_alter_merge_l (g g1 : option A  option A) m1 m2 i :
  g (f (m1 !! i) (m2 !! i)) = f (g1 (m1 !! i)) (m2 !! i) 
  partial_alter g i (merge f m1 m2) = merge f (partial_alter g1 i m1) m2.
Proof.
  intro. apply map_eq. intros j. destruct (decide (i = j)); subst.
  * by rewrite (lookup_merge _), !lookup_partial_alter, !(lookup_merge _).
  * by rewrite (lookup_merge _), !lookup_partial_alter_ne, (lookup_merge _).
Qed.
Lemma partial_alter_merge_r (g g2 : option A  option A) m1 m2 i :
  g (f (m1 !! i) (m2 !! i)) = f (m1 !! i) (g2 (m2 !! i)) 
  partial_alter g i (merge f m1 m2) = merge f m1 (partial_alter g2 i m2).
Proof.
  intro. apply map_eq. intros j. destruct (decide (i = j)); subst.
  * by rewrite (lookup_merge _), !lookup_partial_alter, !(lookup_merge _).
  * by rewrite (lookup_merge _), !lookup_partial_alter_ne, (lookup_merge _).
Qed.

Lemma insert_merge_l m1 m2 i x :
  f (Some x) (m2 !! i) = Some x 
  <[i:=x]>(merge f m1 m2) = merge f (<[i:=x]>m1) m2.
Proof.
  intros. unfold insert, map_insert, alter, map_alter.
  by apply partial_alter_merge_l.
Qed.
Lemma insert_merge_r m1 m2 i x :
  f (m1 !! i) (Some x) = Some x 
  <[i:=x]>(merge f m1 m2) = merge f m1 (<[i:=x]>m2).
Proof.
  intros. unfold insert, map_insert, alter, map_alter.
  by apply partial_alter_merge_r.
Qed.
End merge.

(** ** Properties on the [map_intersection_forall] relation *)
Section intersection_forall.
Context {A} (R : relation A).

Global Instance map_intersection_forall_sym:
  Symmetric R  Symmetric (map_intersection_forall R).
Proof. firstorder auto. Qed.
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Lemma map_intersection_forall_empty_l (m : M A) : map_intersection_forall R  m.
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Proof. intros ???. by rewrite lookup_empty. Qed.
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Lemma map_intersection_forall_empty_r (m : M A) : map_intersection_forall R m .
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Proof. intros ???. by rewrite lookup_empty. Qed.

Lemma map_intersection_forall_alt (m1 m2 : M A) :
  map_intersection_forall R m1 m2 
    map_forall (λ _, curry R) (merge (λ x y,
      match x, y with
      | Some x, Some y => Some (x,y)
      | _, _ => None
      end) m1 m2).
Proof.
  split.
  * intros Hm12 i [x y]. rewrite lookup_merge by done. intros.
    destruct (m1 !! i) eqn:?, (m2 !! i) eqn:?; simplify_equality.
    eapply Hm12; eauto.
  * intros Hm12 i x y ??. apply (Hm12 i (x,y)).
    rewrite lookup_merge by done. by simplify_option_equality.
Qed.

(** Due to the finiteness of finite maps, we can extract a witness if the
relation does not hold. *)
Lemma map_not_intersection_forall `{ x y, Decision (R x y)} (m1 m2 : M A) :
  ¬map_intersection_forall R m1 m2
      i x1 x2, m1 !! i = Some x1  m2 !! i = Some x2  ¬R x1 x2.
Proof.
  split.
  * rewrite map_intersection_forall_alt, (map_not_forall _).
    intros (i & [x y] & Hm12 & ?). rewrite lookup_merge in Hm12 by done.
    exists i x y. by destruct (m1 !! i), (m2 !! i); simplify_equality.
  * intros (i & x1 & x2 & Hx1 & Hx2 & Hx1x2) Hm12.
    by apply Hx1x2, (Hm12 i x1 x2).
Qed.
End intersection_forall.

(** ** Properties on the disjoint maps *)
Lemma map_disjoint_alt {A} (m1 m2 : M A) :
  m1  m2   i, m1 !! i = None  m2 !! i = None.
Proof.
  split; intros Hm1m2 i; specialize (Hm1m2 i);
    destruct (m1 !! i), (m2 !! i); naive_solver.
Qed.
Lemma map_not_disjoint {A} (m1 m2 : M A) :
  ¬m1  m2   i x1 x2, m1 !! i = Some x1  m2 !! i = Some x2.
Proof.
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  unfold disjoint, map_disjoint. rewrite map_not_intersection_forall.
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  * naive_solver.
  * right. auto.
Qed.

Global Instance: Symmetric (@disjoint (M A) _).
Proof. intro. apply map_intersection_forall_sym. auto. Qed.
Lemma map_disjoint_empty_l {A} (m : M A) :   m.
Proof. apply map_intersection_forall_empty_l. Qed.
Lemma map_disjoint_empty_r {A} (m : M A) : m  .
Proof. apply map_intersection_forall_empty_r. Qed.

Lemma map_disjoint_weaken {A} (m1 m1' m2 m2' : M A) :
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  m1'  m2'  m1  m1'  m2  m2'  m1  m2.
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Proof.
  intros Hdisjoint Hm1 Hm2 i x1 x2 Hx1 Hx2.
  destruct (Hdisjoint i x1 x2); auto.
Qed.
Lemma map_disjoint_weaken_l {A} (m1 m1' m2  : M A) :
  m1'  m2  m1  m1'  m1  m2.
Proof. eauto using map_disjoint_weaken. Qed.
Lemma map_disjoint_weaken_r {A} (m1 m2 m2' : M A) :
  m1  m2'  m2  m2'  m1  m2.
Proof. eauto using map_disjoint_weaken. Qed.

Lemma map_disjoint_Some_l {A} (m1 m2 : M A) i x:
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  m1  m2  m1 !! i = Some x  m2 !! i = None.
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Proof.
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  intros Hdisjoint ?. rewrite eq_None_not_Some.
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  intros [x2 ?]. by apply (Hdisjoint i x x2).
Qed.
Lemma map_disjoint_Some_r {A} (m1 m2 : M A) i x:
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  m1  m2  m2 !! i = Some x  m1 !! i = None.
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Proof. rewrite (symmetry_iff ()). apply map_disjoint_Some_l. Qed.

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Lemma map_disjoint_singleton_l {A} (m : M A) i x : {[i, x]}  m  m !! i = None.
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Proof.
  split.
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  * intro. apply (map_disjoint_Some_l {[i, x]} _ _ x);
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      auto using lookup_singleton.
  * intros ? j y1 y2. destruct (decide (i = j)); subst.
    + rewrite lookup_singleton. intuition congruence.
    + by rewrite lookup_singleton_ne.
Qed.
Lemma map_disjoint_singleton_r {A} (m : M A) i x :
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  m  {[i, x]}  m !! i = None.
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Proof. by rewrite (symmetry_iff ()), map_disjoint_singleton_l. Qed.

Lemma map_disjoint_singleton_l_2 {A} (m : M A) i x :
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  m !! i = None  {[i, x]}  m.
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Proof. by rewrite map_disjoint_singleton_l. Qed.
Lemma map_disjoint_singleton_r_2 {A} (m : M A) i x :
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  m !! i = None  m  {[i, x]}.
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Proof. by rewrite map_disjoint_singleton_r. Qed.

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Lemma map_disjoint_delete_l {A} (m1 m2 : M A) i : m1  m2  delete i m1  m2.
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Proof.
  rewrite !map_disjoint_alt.
  intros Hdisjoint j. destruct (Hdisjoint j); auto.
  rewrite lookup_delete_None. tauto.
Qed.
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Lemma map_disjoint_delete_r {A} (m1 m2 : M A) i : m1  m2  m1  delete i m2.
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Proof. symmetry. by apply map_disjoint_delete_l. Qed.

(** ** Properties of the [union_with] operation *)
Section union_with.
Context {A} (f : A  A  option A).

Lemma lookup_union_with m1 m2 i z :
  union_with f m1 m2 !! i = z 
    (m1 !! i = None  m2 !! i = None  z = None) 
    ( x, m1 !! i = Some x  m2 !! i = None  z = Some x) 
    ( y, m1 !! i = None  m2 !! i = Some y  z = Some y) 
    ( x y, m1 !! i = Some x  m2 !! i = Some y  z = f x y).
Proof.
  unfold union_with, map_union_with. rewrite (lookup_merge _).
  destruct (m1 !! i), (m2 !! i); compute; naive_solver.
Qed.
Lemma lookup_union_with_Some m1 m2 i z :
  union_with f m1 m2 !! i = Some z 
    (m1 !! i = Some z  m2 !! i = None) 
    (m1 !! i = None  m2 !! i = Some z) 
    ( x y, m1 !! i = Some x  m2 !! i = Some y  f x y = Some z).
Proof. rewrite lookup_union_with. naive_solver. Qed.
Lemma lookup_union_with_None m1 m2 i :
  union_with f m1 m2 !! i = None 
    (m1 !! i = None  m2 !! i = None) 
    ( x y, m1 !! i = Some x  m2 !! i = Some y  f x y = None).
Proof. rewrite lookup_union_with. naive_solver. Qed.

Lemma lookup_union_with_Some_lr m1 m2 i x y z :
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  m1 !! i = Some x  m2 !! i = Some y  f x y = Some z 
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  union_with f m1 m2 !! i = Some z.
Proof. rewrite lookup_union_with. naive_solver. Qed.
Lemma lookup_union_with_Some_l m1 m2 i x :
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  m1 !! i = Some x  m2 !! i = None  union_with f m1 m2 !! i = Some x.
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Proof. rewrite lookup_union_with. naive_solver. Qed.
Lemma lookup_union_with_Some_r m1 m2 i y :
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  m1 !! i = None  m2 !! i = Some y  union_with f m1 m2 !! i = Some y.
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Proof. rewrite lookup_union_with. naive_solver. Qed.

Global Instance: LeftId (@eq (M A))  (union_with f).
Proof. unfold union_with, map_union_with. apply _. Qed.
Global Instance: RightId (@eq (M A))  (union_with f).
Proof. unfold union_with, map_union_with. apply _. Qed.

Lemma union_with_commutative m1 m2 :
  ( i x y, m1 !! i = Some x  m2 !! i = Some y  f x y = f y x) 
  union_with f m1 m2 = union_with f m2 m1.
Proof.
  intros. apply (merge_commutative _). intros i.
  destruct (m1 !! i) eqn:?, (m2 !! i) eqn:?; simpl; eauto.
Qed.
Global Instance: Commutative (=) f  Commutative (@eq (M A)) (union_with f).
Proof. intros ???. apply union_with_commutative. eauto. Qed.

Lemma union_with_idempotent m :
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  ( i x, m !! i = Some x  f x x = Some x)  union_with f m m = m.
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Proof.
  intros. apply (merge_idempotent _). intros i.
  destruct (m !! i) eqn:?; simpl; eauto.
Qed.

Lemma alter_union_with (g : A  A) m1 m2 i :
  ( x y, m1 !! i = Some x  m2 !! i = Some y  g <$> f x y = f (g x) (g y)) 
  alter g i (union_with f m1 m2) =
    union_with f (alter g i m1) (alter g i m2).
Proof.
  intros. apply (partial_alter_merge _).
  destruct (m1 !! i) eqn:?, (m2 !! i) eqn:?; simpl; eauto.
Qed.
Lemma alter_union_with_l (g : A  A) m1 m2 i :
  ( x y, m1 !! i = Some x  m2 !! i = Some y  g <$> f x y = f (g x) y) 
  ( y, m1 !! i = None  m2 !! i = Some y  g y = y) 
  alter g i (union_with f m1 m2) = union_with f (alter g i m1) m2.
Proof.
  intros. apply (partial_alter_merge_l _).
  destruct (m1 !! i) eqn:?, (m2 !! i) eqn:?; simpl; eauto using f_equal.
Qed.
Lemma alter_union_with_r (g : A  A) m1 m2 i :
  ( x y, m1 !! i = Some x  m2 !! i = Some y  g <$> f x y = f x (g y)) 
  ( x, m1 !! i = Some x  m2 !! i = None  g x = x) 
  alter g i (union_with f m1 m2) = union_with f m1 (alter g i m2).
Proof.
  intros. apply (partial_alter_merge_r _).
  destruct (m1 !! i) eqn:?, (m2 !! i) eqn:?; simpl; eauto using f_equal.
Qed.

Lemma delete_union_with m1 m2 i :
  delete i (union_with f m1 m2) = union_with f (delete i m1) (delete i m2).
Proof. by apply (partial_alter_merge _). Qed.

Lemma delete_list_union_with (m1 m2 : M A) is :
  delete_list is (union_with f m1 m2) =
    union_with f (delete_list is m1) (delete_list is m2).
Proof. induction is; simpl. done. by rewrite IHis, delete_union_with. Qed.

Lemma insert_union_with m1 m2 i x :
  ( x, f x x = Some x) 
  <[i:=x]>(union_with f m1 m2) = union_with f (<[i:=x]>m1) (<[i:=x]>m2).
Proof. intros. apply (partial_alter_merge _). simpl. auto. Qed.
Lemma insert_union_with_l m1 m2 i x :
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  m2 !! i = None  <[i:=x]>(union_with f m1 m2) = union_with f (<[i:=x]>m1) m2.
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Proof.
  intros Hm2. unfold union_with, map_union_with.
  rewrite (insert_merge_l _). done. by rewrite Hm2.
Qed.
Lemma insert_union_with_r m1 m2 i x :
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  m1 !! i = None  <[i:=x]>(union_with f m1 m2) = union_with f m1 (<[i:=x]>m2).