(************************************************************************)
(*         *      The Rocq Prover / The Rocq Development Team           *)
(*  v      *         Copyright INRIA, CNRS and contributors             *)
(* <O___,, * (see version control and CREDITS file for authors & dates) *)
(*   \VV/  **************************************************************)
(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
(*         *     (see LICENSE file for the text of the license)         *)
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(** * Finite set library *)
(** Set interfaces, inspired by the one of Ocaml. When compared with Ocaml, the main differences are: - the lack of [iter] function, useless since Coq is purely functional - the use of [option] types instead of [Not_found] exceptions - the use of [nat] instead of [int] for the [cardinal] function  Several variants of the set interfaces are available: - [WSetsOn] : functorial signature for weak sets - [WSets]   : self-contained version of [WSets] - [SetsOn]  : functorial signature for ordered sets - [Sets]    : self-contained version of [Sets] - [WRawSets] : a signature for weak sets that may be ill-formed - [RawSets]  : same for ordered sets  If unsure, [S = Sets] is probably what you're looking for: most other signatures are subsets of it, while [Sets] can be obtained from [RawSets] via the use of a subset type (see (W)Raw2Sets below). *)
Require Export Bool SetoidList RelationClasses Morphisms
RelationPairs Equalities Orders OrdersFacts.
Set Implicit Arguments.
Unset Strict Implicit.
Module Type TypElt.
Parameters t elt : Type.
End TypElt.
Module Type HasWOps (Import T:TypElt).
Parameter empty : t.
(** The empty set. *)
Parameter is_empty : t -> bool.
(** Test whether a set is empty or not. *)
Parameter mem : elt -> t -> bool.
(** [mem x s] tests whether [x] belongs to the set [s]. *)
Parameter add : elt -> t -> t.
(** [add x s] returns a set containing all elements of [s], plus [x]. If [x] was already in [s], [s] is returned unchanged. *)
Parameter singleton : elt -> t.
(** [singleton x] returns the one-element set containing only [x]. *)
Parameter remove : elt -> t -> t.
(** [remove x s] returns a set containing all elements of [s], except [x]. If [x] was not in [s], [s] is returned unchanged. *)
Parameter union : t -> t -> t.
(** Set union. *)
Parameter inter : t -> t -> t.
(** Set intersection. *)
Parameter diff : t -> t -> t.
(** Set difference. *)
Parameter equal : t -> t -> bool.
(** [equal s1 s2] tests whether the sets [s1] and [s2] are equal, that is, contain equal elements. *)
Parameter subset : t -> t -> bool.
(** [subset s1 s2] tests whether the set [s1] is a subset of the set [s2]. *)
Parameter fold : forall A : Type, (elt -> A -> A) -> t -> A -> A.
(** [fold f s a] computes [(f xN ... (f x2 (f x1 a))...)], where [x1 ... xN] are the elements of [s]. The order in which elements of [s] are presented to [f] is unspecified. *)
Parameter for_all : (elt -> bool) -> t -> bool.
(** [for_all p s] checks if all elements of the set satisfy the predicate [p]. *)
Parameter exists_ : (elt -> bool) -> t -> bool.
(** [exists p s] checks if at least one element of the set satisfies the predicate [p]. *)
Parameter filter : (elt -> bool) -> t -> t.
(** [filter p s] returns the set of all elements in [s] that satisfy predicate [p]. *)
Parameter partition : (elt -> bool) -> t -> t * t.
(** [partition p s] returns a pair of sets [(s1, s2)], where [s1] is the set of all the elements of [s] that satisfy the predicate [p], and [s2] is the set of all the elements of [s] that do not satisfy [p]. *)
Parameter cardinal : t -> nat.
(** Return the number of elements of a set. *)
Parameter elements : t -> list elt.
(** Return the list of all elements of the given set, in any order. *)
Parameter choose : t -> option elt.
(** Return one element of the given set, or [None] if the set is empty. Which element is chosen is unspecified. Equal sets could return different elements. *)
End HasWOps.
Module Type WOps (E : DecidableType).
Definition elt := E.t.
Parameter t : Type. (** the abstract type of sets *)
Include HasWOps.
End WOps.
(** ** Functorial signature for weak sets  Weak sets are sets without ordering on base elements, only a decidable equality. *)
Module Type WSetsOn (E : DecidableType).
(** First, we ask for all the functions *)
Include WOps E.
(** Logical predicates *)
Parameter In : elt -> t -> Prop.
#[global]
Declare Instance In_compat : Proper (E.eq==>eq==>iff) In.
Definition Equal s s' := forall a : elt, In a s <-> In a s'.
Definition Subset s s' := forall a : elt, In a s -> In a s'.
Definition Empty s := forall a : elt, ~ In a s.
Definition For_all (P : elt -> Prop) s := forall x, In x s -> P x.
Definition Exists (P : elt -> Prop) s := exists x, In x s /\ P x.
Notation "s  [=]  t" := (Equal s t) (at level 70, no associativity).
Notation "s  [<=]  t" := (Subset s t) (at level 70, no associativity).
Definition eq : t -> t -> Prop := Equal.
Include IsEq. (** [eq] is obviously an equivalence, for subtyping only *)
Include HasEqDec.
(** Specifications of set operators *)
Section Spec.
Variable s s': t.
Variable x y : elt.
Variable f : elt -> bool.
Notation compatb := (Proper (E.eq==>Logic.eq)) (only parsing).
Parameter mem_spec : mem x s = true <-> In x s.
Parameter equal_spec : equal s s' = true <-> s[=]s'.
Parameter subset_spec : subset s s' = true <-> s[<=]s'.
Parameter empty_spec : Empty empty.
Parameter is_empty_spec : is_empty s = true <-> Empty s.
Parameter add_spec : In y (add x s) <-> E.eq y x \/ In y s.
Parameter remove_spec : In y (remove x s) <-> In y s /\ ~E.eq y x.
Parameter singleton_spec : In y (singleton x) <-> E.eq y x.
Parameter union_spec : In x (union s s') <-> In x s \/ In x s'.
Parameter inter_spec : In x (inter s s') <-> In x s /\ In x s'.
Parameter diff_spec : In x (diff s s') <-> In x s /\ ~In x s'.
Parameter fold_spec : forall (A : Type) (i : A) (f : elt -> A -> A),
fold f s i = fold_left (flip f) (elements s) i.
Parameter cardinal_spec : cardinal s = length (elements s).
Parameter filter_spec : compatb f ->
(In x (filter f s) <-> In x s /\ f x = true).
Parameter for_all_spec : compatb f ->
(for_all f s = true <-> For_all (fun x => f x = true) s).
Parameter exists_spec : compatb f ->
(exists_ f s = true <-> Exists (fun x => f x = true) s).
Parameter partition_spec1 : compatb f ->
fst (partition f s) [=] filter f s.
Parameter partition_spec2 : compatb f ->
snd (partition f s) [=] filter (fun x => negb (f x)) s.
Parameter elements_spec1 : InA E.eq x (elements s) <-> In x s.
(** When compared with ordered sets, here comes the only property that is really weaker: *)
Parameter elements_spec2w : NoDupA E.eq (elements s).
Parameter choose_spec1 : choose s = Some x -> In x s.
Parameter choose_spec2 : choose s = None -> Empty s.
End Spec.
End WSetsOn.
(** ** Static signature for weak sets  Similar to the functorial signature [WSetsOn], except that the module [E] of base elements is incorporated in the signature. *)
Module Type WSets.
Declare Module E : DecidableType.
Include WSetsOn E.
End WSets.
(** ** Functorial signature for sets on ordered elements  Based on [WSetsOn], plus ordering on sets and [min_elt] and [max_elt] and some stronger specifications for other functions. *)
Module Type HasOrdOps (Import T:TypElt).
Parameter compare : t -> t -> comparison.
(** Total ordering between sets. Can be used as the ordering function for doing sets of sets. *)
Parameter min_elt : t -> option elt.
(** Return the smallest element of the given set (with respect to the [E.compare] ordering), or [None] if the set is empty. *)
Parameter max_elt : t -> option elt.
(** Same as [min_elt], but returns the largest element of the given set. *)
End HasOrdOps.
Module Type Ops (E : OrderedType) := WOps E <+ HasOrdOps.
Module Type SetsOn (E : OrderedType).
Include WSetsOn E <+ HasOrdOps <+ HasLt <+ IsStrOrder.
Section Spec.
Variable s s': t.
Variable x y : elt.
Parameter compare_spec : CompSpec eq lt s s' (compare s s').
(** Additional specification of [elements] *)
Parameter elements_spec2 : sort E.lt (elements s).
(** Remark: since [fold] is specified via [elements], this stronger specification of [elements] has an indirect impact on [fold], which can now be proved to receive elements in increasing order. *)
Parameter min_elt_spec1 : min_elt s = Some x -> In x s.
Parameter min_elt_spec2 : min_elt s = Some x -> In y s -> ~ E.lt y x.
Parameter min_elt_spec3 : min_elt s = None -> Empty s.
Parameter max_elt_spec1 : max_elt s = Some x -> In x s.
Parameter max_elt_spec2 : max_elt s = Some x -> In y s -> ~ E.lt x y.
Parameter max_elt_spec3 : max_elt s = None -> Empty s.
(** Additional specification of [choose] *)
Parameter choose_spec3 : choose s = Some x -> choose s' = Some y ->
Equal s s' -> E.eq x y.
End Spec.
End SetsOn.
(** ** Static signature for sets on ordered elements  Similar to the functorial signature [SetsOn], except that the module [E] of base elements is incorporated in the signature. *)
Module Type Sets.
Declare Module E : OrderedType.
Include SetsOn E.
End Sets.
Module Type S := Sets.
(** ** Some subtyping tests << WSetsOn ---> WSets |           | |           | V           V SetsOn  ---> Sets  Module S_WS (M : Sets) <: WSets := M. Module Sfun_WSfun (E:OrderedType)(M : SetsOn E) <: WSetsOn E := M. Module S_Sfun (M : Sets) <: SetsOn M.E := M. Module WS_WSfun (M : WSets) <: WSetsOn M.E := M. >> *)
(** ** Signatures for set representations with ill-formed values.  Motivation:  For many implementation of finite sets (AVL trees, sorted lists, lists without duplicates), we use the same two-layer approach:  - A first module deals with the datatype (eg. list or tree) without any restriction on the values we consider. In this module (named "Raw" in the past), some results are stated under the assumption that some invariant (e.g. sortedness) holds for the input sets. We also prove that this invariant is preserved by set operators.  - A second module implements the exact Sets interface by using a subtype, for instance [{ l : list A | sorted l }]. This module is a mere wrapper around the first Raw module.  With the interfaces below, we give some respectability to the "Raw" modules. This allows the interested users to directly access them via the interfaces. Even better, we can build once and for all a functor doing the transition between Raw and usual Sets.  Description:  The type [t] of sets may contain ill-formed values on which our set operators may give wrong answers. In particular, [mem] may not see a element in a ill-formed set (think for instance of a unsorted list being given to an optimized [mem] that stops its search as soon as a strictly larger element is encountered).  Unlike optimized operators, the [In] predicate is supposed to always be correct, even on ill-formed sets. Same for [Equal] and other logical predicates.  A predicate parameter [Ok] is used to discriminate between well-formed and ill-formed values. Some lemmas hold only on sets validating [Ok]. This predicate [Ok] is required to be preserved by set operators. Moreover, a boolean function [isok] should exist for identifying (at least some of) the well-formed sets.  *)
Module Type WRawSets (E : DecidableType).
(** First, we ask for all the functions *)
Include WOps E.
(** Is a set well-formed or ill-formed ? *)
Parameter IsOk : t -> Prop.
Class Ok (s:t) : Prop := ok : IsOk s.
(** In order to be able to validate (at least some) particular sets as well-formed, we ask for a boolean function for (semi-)deciding predicate [Ok]. If [Ok] isn't decidable, [isok] may be the always-false function. *)
Parameter isok : t -> bool.
(** MS: Dangerous instance, the [isok s = true] hypothesis cannot be discharged with typeclass resolution. Is it really an instance? *)
#[global]
Declare Instance isok_Ok s `(isok s = true) : Ok s | 10.
(** Logical predicates *)
Parameter In : elt -> t -> Prop.
#[global]
Declare Instance In_compat : Proper (E.eq==>eq==>iff) In.
Definition Equal s s' := forall a : elt, In a s <-> In a s'.
Definition Subset s s' := forall a : elt, In a s -> In a s'.
Definition Empty s := forall a : elt, ~ In a s.
Definition For_all (P : elt -> Prop) s := forall x, In x s -> P x.
Definition Exists (P : elt -> Prop) s := exists x, In x s /\ P x.
Notation "s  [=]  t" := (Equal s t) (at level 70, no associativity).
Notation "s  [<=]  t" := (Subset s t) (at level 70, no associativity).
Definition eq : t -> t -> Prop := Equal.
#[global]
Declare Instance eq_equiv : Equivalence eq.
(** First, all operations are compatible with the well-formed predicate. *)
#[global]
Declare Instance empty_ok : Ok empty.
#[global]
Declare Instance add_ok s x `(Ok s) : Ok (add x s).
#[global]
Declare Instance remove_ok s x `(Ok s) : Ok (remove x s).
#[global]
Declare Instance singleton_ok x : Ok (singleton x).
#[global]
Declare Instance union_ok s s' `(Ok s, Ok s') : Ok (union s s').
#[global]
Declare Instance inter_ok s s' `(Ok s, Ok s') : Ok (inter s s').
#[global]
Declare Instance diff_ok s s' `(Ok s, Ok s') : Ok (diff s s').
#[global]
Declare Instance filter_ok s f `(Ok s) : Ok (filter f s).
#[global]
Declare Instance partition_ok1 s f `(Ok s) : Ok (fst (partition f s)).
#[global]
Declare Instance partition_ok2 s f `(Ok s) : Ok (snd (partition f s)).
(** Now, the specifications, with constraints on the input sets. *)
Section Spec.
Variable s s': t.
Variable x y : elt.
Variable f : elt -> bool.
Notation compatb := (Proper (E.eq==>Logic.eq)) (only parsing).
Parameter mem_spec : forall `{Ok s}, mem x s = true <-> In x s.
Parameter equal_spec : forall `{Ok s, Ok s'},
equal s s' = true <-> s[=]s'.
Parameter subset_spec : forall `{Ok s, Ok s'},
subset s s' = true <-> s[<=]s'.
Parameter empty_spec : Empty empty.
Parameter is_empty_spec : is_empty s = true <-> Empty s.
Parameter add_spec : forall `{Ok s},
In y (add x s) <-> E.eq y x \/ In y s.
Parameter remove_spec : forall `{Ok s},
In y (remove x s) <-> In y s /\ ~E.eq y x.
Parameter singleton_spec : In y (singleton x) <-> E.eq y x.
Parameter union_spec : forall `{Ok s, Ok s'},
In x (union s s') <-> In x s \/ In x s'.
Parameter inter_spec : forall `{Ok s, Ok s'},
In x (inter s s') <-> In x s /\ In x s'.
Parameter diff_spec : forall `{Ok s, Ok s'},
In x (diff s s') <-> In x s /\ ~In x s'.
Parameter fold_spec : forall (A : Type) (i : A) (f : elt -> A -> A),
fold f s i = fold_left (flip f) (elements s) i.
Parameter cardinal_spec : forall `{Ok s},
cardinal s = length (elements s).
Parameter filter_spec : compatb f ->
(In x (filter f s) <-> In x s /\ f x = true).
Parameter for_all_spec : compatb f ->
(for_all f s = true <-> For_all (fun x => f x = true) s).
Parameter exists_spec : compatb f ->
(exists_ f s = true <-> Exists (fun x => f x = true) s).
Parameter partition_spec1 : compatb f ->
fst (partition f s) [=] filter f s.
Parameter partition_spec2 : compatb f ->
snd (partition f s) [=] filter (fun x => negb (f x)) s.
Parameter elements_spec1 : InA E.eq x (elements s) <-> In x s.
Parameter elements_spec2w : forall `{Ok s}, NoDupA E.eq (elements s).
Parameter choose_spec1 : choose s = Some x -> In x s.
Parameter choose_spec2 : choose s = None -> Empty s.
End Spec.
End WRawSets.
(** From weak raw sets to weak usual sets *)
Module WRaw2SetsOn (E:DecidableType)(M:WRawSets E) <: WSetsOn E.
(** We avoid creating induction principles for the Record *)
Local Unset Elimination Schemes.
Definition elt := E.t.
Record t_ := Mkt {this :> M.t; is_ok : M.Ok this}.
Definition t := t_.
Arguments Mkt this {is_ok}.
#[global]
Hint Resolve is_ok : typeclass_instances.
Definition In (x : elt)(s : t) := M.In x (this s).
Definition Equal (s s' : t) := forall a : elt, In a s <-> In a s'.
Definition Subset (s s' : t) := forall a : elt, In a s -> In a s'.
Definition Empty (s : t) := forall a : elt, ~ In a s.
Definition For_all (P : elt -> Prop)(s : t) := forall x, In x s -> P x.
Definition Exists (P : elt -> Prop)(s : t) := exists x, In x s /\ P x.
Definition mem (x : elt)(s : t) := M.mem x s.
Definition add (x : elt)(s : t) : t := Mkt (M.add x s).
Definition remove (x : elt)(s : t) : t := Mkt (M.remove x s).
Definition singleton (x : elt) : t := Mkt (M.singleton x).
Definition union (s s' : t) : t := Mkt (M.union s s').
Definition inter (s s' : t) : t := Mkt (M.inter s s').
Definition diff (s s' : t) : t := Mkt (M.diff s s').
Definition equal (s s' : t) := M.equal s s'.
Definition subset (s s' : t) := M.subset s s'.
Definition empty : t := Mkt M.empty.
Definition is_empty (s : t) := M.is_empty s.
Definition elements (s : t) : list elt := M.elements s.
Definition choose (s : t) : option elt := M.choose s.
Definition fold (A : Type)(f : elt -> A -> A)(s : t) : A -> A := M.fold f s.
Definition cardinal (s : t) := M.cardinal s.
Definition filter (f : elt -> bool)(s : t) : t := Mkt (M.filter f s).
Definition for_all (f : elt -> bool)(s : t) := M.for_all f s.
Definition exists_ (f : elt -> bool)(s : t) := M.exists_ f s.
Definition partition (f : elt -> bool)(s : t) : t * t :=
let p := M.partition f s in (Mkt (fst p), Mkt (snd p)).
#[global]
Instance In_compat : Proper (E.eq==>eq==>iff) In.
#[global]
Instance lt_compat : Proper (eq==>eq==>iff) lt.
Section Spec.
Variable s s' s'' : t.
Variable x y : elt.

(* Specifications: *)
Lemma compare_spec : CompSpec eq lt s s' (compare s s').
Definition Below x s := forall y, In y s -> O.lt y x.