(* 052_the_number_of_subsets_of_a_set — rocq *)

(* (c) Copyright 2006-2016 Microsoft Corporation and Inria.                  *)
(* Distributed under the terms of CeCILL-B.                                  *)
From HB Require Import structures.
From mathcomp Require Import ssreflect ssrbool ssrfun eqtype ssrnat div seq.
From mathcomp Require Import choice fintype finfun bigop.

(******************************************************************************)
(* This file defines a type for sets over a finite Type, similar to the type  *)
(* of functions over a finite Type defined in finfun.v (indeed, based in it): *)
(* {set T} where T must have a finType structure.                             *)
(* We equip {set T} itself with a finType structure, hence Leibnitz and       *)
(* extensional equalities coincide on {set T}, and we can form {set {set T}}. *)
(*   If A, B : {set T} and P : {set {set T}}, we define:                      *)
(*           x \in A == x belongs to A (i.e., {set T} implements predType,    *)
(*                      by coercion to pred_sort)                             *)
(*             mem A == the predicate corresponding to A                      *)
(*          finset p == the set corresponding to a predicate p                *)
(*       [set x | P] == the set containing the x such that P is true (x may   *)
(*                      appear in P)                                          *)
(*   [set x | P & Q] := [set x | P && Q]                                      *)
(*      [set x in A] == the set containing the x in a collective predicate A  *)
(*  [set x in A | P] == the set containing the x in A such that P is true     *)
(* [set x in A | P & Q] := [set x in A | P && Q]                              *)
(*  All these have typed variants [set x : T | P], [set x : T in A], etc.     *)
(*              set0 == the empty set                                         *)
(*  [set: T] or setT == the full set (the A containing all x : T)             *)
(*           [set x] == the singleton {x}                                     *)
(*          [set~ x] == the complement of the singleton {x}                   *)
(*         [set:: s] == the set spanned by the sequence s                     *)
(* [set a1; a2;...; an] := a1 |: [set a2] :|: ... :|: [set an]                *)
(*           A :|: B == the union of A and B                                  *)
(*            x |: A == A with the element x added (:= [set x] :|: A)         *)
(*           A :&: B == the intersection of A and B                           *)
(*              ~: A == the complement of A                                   *)
(*           A :\: B == the difference A minus B                              *)
(*            A :\ x == A with the element x removed (:= A :\: [set x])       *)
(* \bigcup_<range> A == the union of all A, for i in <range> (i is bound in   *)
(*                      A, see bigop.v)                                       *)
(* \bigcap_<range> A == the intersection of all A, for i in <range>           *)
(*           cover P == the union of the set of sets P                        *)
(*        trivIset P <=> the elements of P are pairwise disjoint              *)
(*     partition P A <=> P is a partition of A                                *)
(*        pblock P x == a block of P containing x, or else set0               *)
(* equivalence_partition R D == the partition induced on D by the relation R  *)
(*                       (provided R is an equivalence relation in D)         *)
(* preim_partition f D == the partition induced on D by the equivalence       *)
(*                      [rel x y | f x == f y]                                *)
(* is_transversal X P D <=> X is a transversal of the partition P of D        *)
(*   transversal P D == a transversal of P, provided P is a partition of D    *)
(* transversal_repr x0 X B == a representative of B \in P selected by the     *)
(*                      transversal X of P, or else x0                        *)
(*        powerset A == the set of all subset of the set A                    *)
(*          P ::&: A == those sets in P that are subsets of the set A         *)
(*        setX A1 A2 == cartesian product of A1 and A2                        *)
(*                   := [set u | u.1 \in A1 & u.2 \in A2]                     *)
(*       setXn I f A == indexed cartesian product of                          *)
(*                      A : forall i : I, {set f i}                           *)
(*         f @^-1: A == the preimage of the collective predicate A under f    *)
(*            f @: A == the image set of the collective predicate A by f      *)
(*       f @2:(A, B) == the image set of A x B by the binary function f       *)
(*  [set E | x in A] == the set of all the values of the expression E, for x  *)
(*                      drawn from the collective predicate A                 *)
(* [set E | x in A & P] == the set of values of E for x drawn from A, such    *)
(*                      that P is true                                        *)
(* [set E | x in A, y in B] == the set of values of E for x drawn from A and  *)
(*                      and y drawn from B; B may depend on x                 *)
(* [set E | x in A, y in B & P] == the set of values of E for x drawn from A  *)
(*                      y drawn from B, such that P is true                   *)
(*   [set E | x : T] == the set of all values of E, with x in type T          *)
(* [set E | x : T & P] == the set of values of E for x : T s.t. P is true     *)
(* [set E | x : T, y : U in B], [set E | x : T, y : U in B & P],              *)
(* [set E | x : T in A, y : U], [set E | x : T in A, y : U & P],              *)
(* [set E | x : T, y : U], [set E | x : T, y : U & P]                         *)
(*                   == type-ranging versions of the binary comprehensions    *)
(* [set E | x : T in A], [set E | x in A, y], [set E | x, y & P], etc.        *)
(*                   == typed and untyped variants of the comprehensions above*)
(*                      The types may be required as type inference processes *)
(*                      E before considering A or B. Note that type casts in  *)
(*                      the binary comprehension must either be both present  *)
(*                      or absent and that there are no untyped variants for  *)
(*                      single-type comprehension as Coq parsing confuses     *)
(*                      [x | P] and [E | x].                                  *)
(*        minset p A == A is a minimal set satisfying p                       *)
(*        maxset p A == A is a maximal set satisfying p                       *)
(*          unset1 A == [pick x in A] if #|A| == 1, else None                 *)
(* fprod_pick I T_ p == pick a function of type (forall i : I, T_ i) provided *)
(*                      a proof p of 0 < #|fprod I T_| is given               *)
(* ftagged I T_ p f i == untag (fprod_pick I T_ p) i (fun x=>x) (f i), useful *)
(*   to lift f : {ffun I -> {i : I & T_ i}} (akin to FProd's building blocks) *)
(*   to a vanilla dependent function of type (forall i : I, T_ i).            *)
(* Provided a monotonous function F : {set T} -> {set T}, we get fixpoints    *)
(*      fixset F := iter #|T| F set0                                          *)
(*               == the least fixpoint of F                                   *)
(*               == the minimal set such that F X == X                        *)
(* fix_order F x == the minimum number of iterations so that                  *)
(*                  x is in iter (fix_order F x) F set0                       *)
(*     funsetC F := fun X => ~: F (~: X)                                      *)
(*    cofixset F == the greatest fixpoint of F                                *)
(*               == the maximal set such that F X == X                        *)
(*               := ~: fixset (funsetC F)                                     *)
(* We also provide notations A :=: B, A :<>: B, A :==: B, A :!=: B, A :=P: B  *)
(* that specialize A = B, A <> B, A == B, etc., to {set _}. This is useful    *)
(* for subtypes of {set T}, such as {group T}, that coerce to {set T}.        *)
(*   We give many lemmas on these operations, on card, and on set inclusion.  *)
(* In addition to the standard suffixes described in ssrbool.v, we associate  *)
(* the following suffixes to set operations:                                  *)
(*  0 -- the empty set, as in in_set0 : (x \in set0) = false                  *)
(*  T -- the full set, as in in_setT : x \in [set: T]                         *)
(*  1 -- a singleton set, as in in_set1 : (x \in [set a]) = (x == a)          *)
(*  2 -- an unordered pair, as in                                             *)
(*          in_set2 : (x \in [set a; b]) = (x == a) || (x == b)               *)
(*  C -- complement, as in setCK : ~: ~: A = A                                *)
(*  I -- intersection, as in setIid : A :&: A = A                             *)
(*  U -- union, as in setUid : A :|: A = A                                    *)
(*  D -- difference, as in setDv : A :\: A = set0                             *)
(*  S -- a subset argument, as in                                             *)
(*         setIS: B \subset C -> A :&: B \subset A :&: C                      *)
(* These suffixes are sometimes preceded with an `s' to distinguish them from *)
(* their basic ssrbool interpretation, e.g.,                                  *)
(*  card1 : #|pred1 x| = 1 and cards1 : #|[set x]| = 1                        *)
(* We also use a trailing `r' to distinguish a right-hand complement from     *)
(* commutativity, e.g.,                                                       *)
(*  setIC : A :&: B = B :&: A and setICr : A :&: ~: A = set0.                 *)
(******************************************************************************)

Set Implicit Arguments.
Unset Strict Implicit.
Unset Printing Implicit Defensive.

Declare Scope set_scope.

Section SetType.

Variable T : finType.

Inductive set_type : predArgType := FinSet of {ffun pred T}.
Definition finfun_of_set A := let: FinSet f := A in f.
Definition set_of := set_type.
Identity Coercion type_of_set_of : set_of >-> set_type.

Definition set_isSub := Eval hnf in [isNew for finfun_of_set].
HB.instance Definition _ := set_isSub.
HB.instance Definition _ := [Finite of set_type by <:].

End SetType.

Delimit Scope set_scope with SET.
Bind Scope set_scope with set_type.
Bind Scope set_scope with set_of.
Open Scope set_scope.
Arguments set_of T%_type.
Arguments finfun_of_set {T} A%_SET.

Notation "{ 'set' T }" := (set_of T) (format "{ 'set'  T }") : type_scope.

(* We later define several subtypes that coerce to set; for these it is       *)
(* preferable to state equalities at the {set _} level, even when comparing   *)
(* subtype values, because the primitive "injection" tactic tends to diverge  *)
(* on complex types (e.g., quotient groups). We provide some parse-only       *)
(* notation to make this technicality less obstructive.                       *)
Notation "A :=: B" := (A = B :> {set _})
  (at level 70, no associativity, only parsing) : set_scope.
Notation "A :<>: B" := (A <> B :> {set _})
  (at level 70, no associativity, only parsing) : set_scope.
Notation "A :==: B" := (A == B :> {set _})
  (at level 70, no associativity, only parsing) : set_scope.
Notation "A :!=: B" := (A != B :> {set _})
  (at level 70, no associativity, only parsing) : set_scope.
Notation "A :=P: B" := (A =P B :> {set _})
  (at level 70, no associativity, only parsing) : set_scope.


HB.lock
Definition finset (T : finType) (P : pred T) : {set T} := @FinSet T (finfun P).
Canonical finset_unlock := Unlockable finset.unlock.

(* The weird type of pred_of_set is imposed by the syntactic restrictions on  *)
(* coercion declarations; it is unfortunately not possible to use a functor   *)
(* to retype the declaration, because this triggers an ugly bug in the Coq    *)
(* coercion chaining code.                                                    *)
HB.lock
Definition pred_of_set T (A : set_type T) : fin_pred_sort (predPredType T)
:= val A.
Canonical pred_of_set_unlock := Unlockable pred_of_set.unlock.

Notation "[ 'set' x : T | P ]" := (finset (fun x : T => P%B))
  (x at level 99, only parsing) : set_scope.
Notation "[ 'set' x | P ]" := [set x : _ | P]
  (P at level 99, format "[ 'set'  x  |  P ]") : set_scope.
Notation "[ 'set' x 'in' A ]" := [set x | x \in A]
  (format "[ 'set'  x  'in'  A ]") : set_scope.
Notation "[ 'set' x : T 'in' A ]" := [set x : T | x \in A]
  (only parsing) : set_scope.
Notation "[ 'set' x : T | P & Q ]" := [set x : T | P && Q]
  (only parsing) : set_scope.
Notation "[ 'set' x | P & Q ]" := [set x | P && Q ]
  (P at level 99, format "[ 'set'  x  |  P  &  Q ]") : set_scope.
Notation "[ 'set' x : T 'in' A | P ]" := [set x : T | x \in A & P]
  (only parsing) : set_scope.
Notation "[ 'set' x 'in' A | P ]" := [set x | x \in A & P]
  (format "[ 'set'  x  'in'  A  |  P ]") : set_scope.
Notation "[ 'set' x 'in' A | P & Q ]" := [set x in A | P && Q]
  (format "[ 'set'  x  'in'  A  |  P  &  Q ]") : set_scope.
Notation "[ 'set' x : T 'in' A | P & Q ]" := [set x : T in A | P && Q]
  (only parsing) : set_scope.

Notation "[ 'set' :: s ]" := (finset [in pred_of_seq s])
  (format "[ 'set' ::  s ]") : set_scope.

(* This lets us use set and subtypes of set, like group or coset_of, both as  *)
(* collective predicates and as arguments of the \pi(_) notation.             *)
Coercion pred_of_set: set_type >-> fin_pred_sort.

(* Declare pred_of_set as a canonical instance of topred, but use the         *)
(* coercion to resolve mem A to @mem (predPredType T) (pred_of_set A).        *)
Canonical set_predType T := @PredType _ (unkeyed (set_type T)) (@pred_of_set T).

Section BasicSetTheory.

Variable T : finType.
Implicit Types (x : T) (A B : {set T}) (pA : pred T).

HB.instance Definition _ := Finite.on {set T}.

Lemma in_set pA x : (x \in finset pA) = pA x.
Proof. by rewrite [@finset]unlock unlock [x \in _]ffunE. Qed.

Lemma setP A B : A =i B <-> A = B.
Proof.
by split=> [eqAB|-> //]; apply/val_inj/ffunP=> x; have:= eqAB x; rewrite unlock.
Qed.

Definition set0 := [set x : T | false].
Definition setTfor := [set x : T | true].

Lemma in_setT x : x \in setTfor.
Proof. by rewrite in_set. Qed.

Lemma eqsVneq A B : eq_xor_neq A B (B == A) (A == B).
Proof. exact: eqVneq. Qed.

Lemma eq_finset (pA pB : pred T) : pA =1 pB -> finset pA = finset pB.
Proof. by move=> eq_p; apply/setP => x; rewrite !(in_set, inE) eq_p. Qed.

End BasicSetTheory.

Arguments eqsVneq {T} A B, {T A B}.

Arguments set0 {T}.
Arguments setTfor T%_type.
Arguments eq_finset {T} [pA] pB eq_pAB.
#[global] Hint Resolve in_setT : core.

Notation "[ 'set' : T ]" := (setTfor T) (format "[ 'set' :  T ]") : set_scope.

Notation setT := [set: _] (only parsing).

HB.lock
Definition set1 (T : finType) (a : T) := [set x | x == a].

Section setOpsDefs.

Variable T : finType.
Implicit Types (a x : T) (A B D : {set T}) (P : {set {set T}}).

Definition setU A B := [set x | (x \in A) || (x \in B)].
Definition setI A B := [set x in A | x \in B].
Definition setC A := [set x | x \notin A].
Definition setD A B := [set x | x \notin B & x \in A].
Definition ssetI P D := [set A in P | A \subset D].
Definition powerset D := [set A : {set T} | A \subset D].

End setOpsDefs.

Notation "[ 'set' a ]" := (set1 a)
  (a at level 99, format "[ 'set'  a ]") : set_scope.
Notation "[ 'set' a : T ]" := [set (a : T)]
  (a at level 99, format "[ 'set'  a   :  T ]") : set_scope.
Notation "A :|: B" := (setU A B) : set_scope.
Notation "a |: A" := ([set a] :|: A) : set_scope.
(* This is left-associative due to historical limitations of the .. Notation. *)
Notation "[ 'set' a1 ; a2 ; .. ; an ]" := (setU .. (a1 |: [set a2]) .. [set an])
  (format "[ 'set'  a1 ;  a2 ;  .. ;  an ]") : set_scope.
Notation "A :&: B" := (setI A B) : set_scope.
Notation "~: A" := (setC A) (at level 35, right associativity) : set_scope.
Notation "[ 'set' ~ a ]" := (~: [set a])
  (format "[ 'set' ~  a ]") : set_scope.
Notation "A :\: B" := (setD A B) : set_scope.
Notation "A :\ a" := (A :\: [set a]) : set_scope.
Notation "P ::&: D" := (ssetI P D) (at level 48) : set_scope.

Section setOps.

Variable T : finType.
Implicit Types (a x : T) (A B C D : {set T}) (pA pB pC : pred T).

Lemma eqEsubset A B : (A == B) = (A \subset B) && (B \subset A).
Proof. by apply/eqP/subset_eqP=> /setP. Qed.

Lemma subEproper A B : (A \subset B) = (A == B) || (A \proper B).
Proof. by rewrite eqEsubset -andb_orr orbN andbT. Qed.

Lemma eqVproper A B : A \subset B -> A = B \/ A \proper B.
Proof. by rewrite subEproper => /predU1P. Qed.

Lemma properEneq A B : (A \proper B) = (A != B) && (A \subset B).
Proof. by rewrite andbC eqEsubset negb_and andb_orr andbN. Qed.

Lemma proper_neq A B : A \proper B -> A != B.
Proof. by rewrite properEneq; case/andP. Qed.

Lemma eqEproper A B : (A == B) = (A \subset B) && ~~ (A \proper B).
Proof. by rewrite negb_and negbK andb_orr andbN eqEsubset. Qed.

Lemma eqEcard A B : (A == B) = (A \subset B) && (#|B| <= #|A|).
Proof.
rewrite eqEsubset; apply: andb_id2l => sAB.
by rewrite (geq_leqif (subset_leqif_card sAB)).
Qed.

Lemma properEcard A B : (A \proper B) = (A \subset B) && (#|A| < #|B|).
Proof. by rewrite properEneq ltnNge andbC eqEcard; case: (A \subset B). Qed.

Lemma subset_leqif_cards A B : A \subset B -> (#|A| <= #|B| ?= iff (A == B)).
Proof. by move=> sAB; rewrite eqEsubset sAB; apply: subset_leqif_card. Qed.

Lemma in_set0 x : (x \in set0) = false.
Proof. by rewrite in_set. Qed.

Lemma sub0set A : set0 \subset A.
Proof. by apply/subsetP=> x; rewrite in_set. Qed.

Lemma subset0 A : (A \subset set0) = (A == set0).
Proof. by rewrite eqEsubset sub0set andbT. Qed.

Lemma proper0 A : (set0 \proper A) = (A != set0).
Proof. by rewrite properE sub0set subset0. Qed.

Lemma subset_neq0 A B : A \subset B -> A != set0 -> B != set0.
Proof. by rewrite -!proper0 => sAB /proper_sub_trans->. Qed.

Lemma set_0Vmem A : (A = set0) + {x : T | x \in A}.
Proof.
case: (pickP (mem A)) => [x Ax | A0]; [by right; exists x | left].
by apply/setP=> x; rewrite in_set; apply: A0.
Qed.

Lemma set_enum A : [set x | x \in enum A] = A.
Proof. by apply/setP => x; rewrite in_set mem_enum. Qed.

Lemma enum_set0 : enum set0 = [::] :> seq T.
Proof. by rewrite (eq_enum (in_set _)) enum0. Qed.

Lemma subsetT A : A \subset setT.
Proof. by apply/subsetP=> x; rewrite in_set. Qed.

Lemma subsetT_hint mA : subset mA (mem [set: T]).
Proof. by rewrite unlock; apply/pred0P=> x; rewrite !inE in_set. Qed.
Hint Resolve subsetT_hint : core.

Lemma subTset A : (setT \subset A) = (A == setT).
Proof. by rewrite eqEsubset subsetT. Qed.

Lemma properT A : (A \proper setT) = (A != setT).
Proof. by rewrite properEneq subsetT andbT. Qed.

Lemma set1P x a : reflect (x = a) (x \in [set a]).
Proof. by rewrite set1.unlock in_set; apply: eqP. Qed.

Lemma enum_setT : enum [set: T] = Finite.enum T.
Proof. by rewrite (eq_enum (in_set _)) enumT. Qed.

Lemma in_set1 x a : (x \in [set a]) = (x == a).
Proof. by rewrite set1.unlock in_set. Qed.

Definition inE := (in_set, in_set1, inE).

Lemma set11 x : x \in [set x].
Proof. by rewrite !inE. Qed.

Lemma set1_inj : injective (@set1 T).
Proof. by move=> a b eqsab; apply/set1P; rewrite -eqsab set11. Qed.

Lemma enum_set1 a : enum [set a] = [:: a].
Proof. by rewrite set1.unlock (eq_enum (in_set _)) enum1. Qed.

Lemma setU1P x a B : reflect (x = a \/ x \in B) (x \in a |: B).
Proof. by rewrite !inE; apply: predU1P. Qed.

Lemma in_setU1 x a B : (x \in a |: B) = (x == a) || (x \in B).
Proof. by rewrite !inE. Qed.

Lemma set_nil : [set:: nil] = @set0 T. Proof. by rewrite -enum_set0 set_enum. Qed.

Lemma set_seq1 a : [set:: [:: a]] = [set a].
Proof. by rewrite -enum_set1 set_enum. Qed.

Lemma set_cons a s : [set:: a :: s] = a |: [set:: s].
Proof. by apply/setP=> x; rewrite !inE. Qed.

Lemma setU11 x B : x \in x |: B.
Proof. by rewrite !inE eqxx. Qed.

Lemma setU1r x a B : x \in B -> x \in a |: B.
Proof. by move=> Bx; rewrite !inE predU1r. Qed.

(* We need separate lemmas for the explicit enumerations since they *)
(* associate on the left.                                           *)
Lemma set1Ul x A b : x \in A -> x \in A :|: [set b].
Proof. by move=> Ax; rewrite !inE Ax. Qed.

Lemma set1Ur A b : b \in A :|: [set b].
Proof. by rewrite !inE eqxx orbT. Qed.

Lemma in_setC1 x a : (x \in [set~ a]) = (x != a).
Proof. by rewrite !inE. Qed.

Lemma setC11 x : (x \in [set~ x]) = false.
Proof. by rewrite !inE eqxx. Qed.

Lemma setD1P x A b : reflect (x != b /\ x \in A) (x \in A :\ b).
Proof. by rewrite !inE; apply: andP. Qed.

Lemma in_setD1 x A b : (x \in A :\ b) = (x != b) && (x \in A) .
Proof. by rewrite !inE. Qed.

Lemma setD11 b A : (b \in A :\ b) = false.
Proof. by rewrite !inE eqxx. Qed.

Lemma setD1K a A : a \in A -> a |: (A :\ a) = A.
Proof. by move=> Aa; apply/setP=> x /[!inE]; case: eqP => // ->. Qed.

Lemma setU1K a B : a \notin B -> (a |: B) :\ a = B.
Proof.
by move/negPf=> nBa; apply/setP=> x /[!inE]; case: eqP => // ->.
Qed.

Lemma set2P x a b : reflect (x = a \/ x = b) (x \in [set a; b]).
Proof. by rewrite !inE; apply: pred2P. Qed.

Lemma in_set2 x a b : (x \in [set a; b]) = (x == a) || (x == b).
Proof. by rewrite !inE. Qed.

Lemma set21 a b : a \in [set a; b].
Proof. by rewrite !inE eqxx. Qed.

Lemma set22 a b : b \in [set a; b].
Proof. by rewrite !inE eqxx orbT. Qed.

Lemma disjoint_set1l pA x : [disjoint [set x] & pA] = (x \notin pA).
Proof.
apply/pred0P/idP=> [/(_ x)/=|]; first by rewrite inE eqxx /= => ->.
by move=> xNA y; rewrite !inE; case: eqP => //= ->; apply/negbTE.
Qed.

Lemma disjoint_set1r pA x : [disjoint pA & [set x]] = (x \notin pA).
Proof. by rewrite disjoint_sym disjoint_set1l. Qed.

Lemma setUP x A B : reflect (x \in A \/ x \in B) (x \in A :|: B).
Proof. by rewrite !inE; apply: orP. Qed.

Lemma in_setU x A B : (x \in A :|: B) = (x \in A) || (x \in B).
Proof. exact: in_set. Qed.

Lemma setUC A B : A :|: B = B :|: A.
Proof. by apply/setP => x; rewrite !inE orbC. Qed.

Lemma setUS A B C : A \subset B -> C :|: A \subset C :|: B.
Proof.
move=> sAB; apply/subsetP=> x; rewrite !inE.
by case: (x \in C) => //; apply: (subsetP sAB).
Qed.

Lemma setSU A B C : A \subset B -> A :|: C \subset B :|: C.
Proof. by move=> sAB; rewrite -!(setUC C) setUS. Qed.

Lemma setUSS A B C D : A \subset C -> B \subset D -> A :|: B \subset C :|: D.
Proof. by move=> /(setSU B) /subset_trans sAC /(setUS C)/sAC. Qed.

Lemma set0U A : set0 :|: A = A.
Proof. by apply/setP => x; rewrite !inE orFb. Qed.

Lemma setU0 A : A :|: set0 = A.
Proof. by rewrite setUC set0U. Qed.

Lemma setUA A B C : A :|: (B :|: C) = A :|: B :|: C.
Proof. by apply/setP => x; rewrite !inE orbA. Qed.

Lemma setUCA A B C : A :|: (B :|: C) = B :|: (A :|: C).
Proof. by rewrite !setUA (setUC B). Qed.

Lemma setUAC A B C : A :|: B :|: C = A :|: C :|: B.
Proof. by rewrite -!setUA (setUC B). Qed.

Lemma setUACA A B C D : (A :|: B) :|: (C :|: D) = (A :|: C) :|: (B :|: D).
Proof. by rewrite -!setUA (setUCA B). Qed.

Lemma setTU A : setT :|: A = setT.
Proof. by apply/setP => x; rewrite !inE orTb. Qed.

Lemma setUT A : A :|: setT = setT.
Proof. by rewrite setUC setTU. Qed.

Lemma setUid A : A :|: A = A.
Proof. by apply/setP=> x; rewrite inE orbb. Qed.

Lemma setUUl A B C : A :|: B :|: C = (A :|: C) :|: (B :|: C).
Proof. by rewrite setUA !(setUAC _ C) -(setUA _ C) setUid. Qed.

Lemma setUUr A B C : A :|: (B :|: C) = (A :|: B) :|: (A :|: C).
Proof. by rewrite !(setUC A) setUUl. Qed.

(* intersection *)

(* setIdP is a generalisation of setIP that applies to comprehensions. *)
Lemma setIdP x pA pB : reflect (pA x /\ pB x) (x \in [set y | pA y & pB y]).
Proof. by rewrite !inE; apply: andP. Qed.

Lemma setId2P x pA pB pC :
  reflect [/\ pA x, pB x & pC x] (x \in [set y | pA y & pB y && pC y]).
Proof. by rewrite !inE; apply: and3P. Qed.

Lemma setIdE A pB : [set x in A | pB x] = A :&: [set x | pB x].
Proof. by apply/setP=> x; rewrite !inE. Qed.

Lemma setIP x A B : reflect (x \in A /\ x \in B) (x \in A :&: B).
Proof. exact: (iffP (@setIdP _ _ _)). Qed.

Lemma in_setI x A B : (x \in A :&: B) = (x \in A) && (x \in B).
Proof. exact: in_set. Qed.

Lemma setIC A B : A :&: B = B :&: A.
Proof. by apply/setP => x; rewrite !inE andbC. Qed.

Lemma setIS A B C : A \subset B -> C :&: A \subset C :&: B.
Proof.
move=> sAB; apply/subsetP=> x; rewrite !inE.
by case: (x \in C) => //; apply: (subsetP sAB).
Qed.

Lemma setSI A B C : A \subset B -> A :&: C \subset B :&: C.
Proof. by move=> sAB; rewrite -!(setIC C) setIS. Qed.

Lemma setISS A B C D : A \subset C -> B \subset D -> A :&: B \subset C :&: D.
Proof. by move=> /(setSI B) /subset_trans sAC /(setIS C) /sAC. Qed.

Lemma setTI A : setT :&: A = A.
Proof. by apply/setP => x; rewrite !inE andTb. Qed.

Lemma setIT A : A :&: setT = A.
Proof. by rewrite setIC setTI. Qed.

Lemma set0I A : set0 :&: A = set0.
Proof. by apply/setP => x; rewrite !inE andFb. Qed.

Lemma setI0 A : A :&: set0 = set0.
Proof. by rewrite setIC set0I. Qed.

Lemma setIA A B C : A :&: (B :&: C) = A :&: B :&: C.
Proof. by apply/setP=> x; rewrite !inE andbA. Qed.

Lemma setICA A B C : A :&: (B :&: C) = B :&: (A :&: C).
Proof. by rewrite !setIA (setIC A). Qed.

Lemma setIAC A B C : A :&: B :&: C = A :&: C :&: B.
Proof. by rewrite -!setIA (setIC B). Qed.

Lemma setIACA A B C D : (A :&: B) :&: (C :&: D) = (A :&: C) :&: (B :&: D).
Proof. by rewrite -!setIA (setICA B). Qed.

Lemma setIid A : A :&: A = A.
Proof. by apply/setP=> x; rewrite inE andbb. Qed.

Lemma setIIl A B C : A :&: B :&: C = (A :&: C) :&: (B :&: C).
Proof. by rewrite setIA !(setIAC _ C) -(setIA _ C) setIid. Qed.

Lemma setIIr A B C : A :&: (B :&: C) = (A :&: B) :&: (A :&: C).
Proof. by rewrite !(setIC A) setIIl. Qed.

(* distribute /cancel *)

Lemma setIUr A B C : A :&: (B :|: C) = (A :&: B) :|: (A :&: C).
Proof. by apply/setP=> x; rewrite !inE andb_orr. Qed.

Lemma setIUl A B C : (A :|: B) :&: C = (A :&: C) :|: (B :&: C).
Proof. by apply/setP=> x; rewrite !inE andb_orl. Qed.

Lemma setUIr A B C : A :|: (B :&: C) = (A :|: B) :&: (A :|: C).
Proof. by apply/setP=> x; rewrite !inE orb_andr. Qed.

Lemma setUIl A B C : (A :&: B) :|: C = (A :|: C) :&: (B :|: C).
Proof. by apply/setP=> x; rewrite !inE orb_andl. Qed.

Lemma setUK A B : (A :|: B) :&: A = A.
Proof. by apply/setP=> x; rewrite !inE orbK. Qed.

Lemma setKU A B : A :&: (B :|: A) = A.
Proof. by apply/setP=> x; rewrite !inE orKb. Qed.

Lemma setIK A B : (A :&: B) :|: A = A.
Proof. by apply/setP=> x; rewrite !inE andbK. Qed.

Lemma setKI A B : A :|: (B :&: A) = A.
Proof. by apply/setP=> x; rewrite !inE andKb. Qed.

(* complement *)

Lemma setCP x A : reflect (~ x \in A) (x \in ~: A).
Proof. by rewrite !inE; apply: negP. Qed.

Lemma in_setC x A : (x \in ~: A) = (x \notin A).
Proof. exact: in_set. Qed.

Lemma setCK : involutive (@setC T).
Proof. by move=> A; apply/setP=> x; rewrite !inE negbK. Qed.

Lemma setC_inj : injective (@setC T).
Proof. exact: can_inj setCK. Qed.

Lemma subsets_disjoint A B : (A \subset B) = [disjoint A & ~: B].
Proof. by rewrite subset_disjoint; apply: eq_disjoint_r => x; rewrite !inE. Qed.

Lemma disjoints_subset A B : [disjoint A & B] = (A \subset ~: B).
Proof. by rewrite subsets_disjoint setCK. Qed.

Lemma powersetCE A B : (A \in powerset (~: B)) = [disjoint A & B].
Proof. by rewrite inE disjoints_subset. Qed.

Lemma setCS A B : (~: A \subset ~: B) = (B \subset A).
Proof. by rewrite !subsets_disjoint setCK disjoint_sym. Qed.

Lemma setCU A B : ~: (A :|: B) = ~: A :&: ~: B.
Proof. by apply/setP=> x; rewrite !inE negb_or. Qed.

Lemma setCI A B : ~: (A :&: B) = ~: A :|: ~: B.
Proof. by apply/setP=> x; rewrite !inE negb_and. Qed.

Lemma setUCr A : A :|: ~: A = setT.
Proof. by apply/setP=> x; rewrite !inE orbN. Qed.

Lemma setICr A : A :&: ~: A = set0.
Proof. by apply/setP=> x; rewrite !inE andbN. Qed.

Lemma setC0 : ~: set0 = [set: T].
Proof. by apply/setP=> x; rewrite !inE. Qed.

Lemma setCT : ~: [set: T] = set0.
Proof. by rewrite -setC0 setCK. Qed.

Lemma properC A B : (~: B \proper ~: A) = (A \proper B).
Proof. by rewrite !properE !setCS. Qed.

(* difference *)

Lemma setDP A B x : reflect (x \in A /\ x \notin B) (x \in A :\: B).
Proof. by rewrite inE andbC; apply: andP. Qed.

Lemma in_setD A B x : (x \in A :\: B) = (x \notin B) && (x \in A).
Proof. exact: in_set. Qed.

Lemma setDE A B : A :\: B = A :&: ~: B.
Proof. by apply/setP => x; rewrite !inE andbC. Qed.

Lemma setSD A B C : A \subset B -> A :\: C \subset B :\: C.
Proof. by rewrite !setDE; apply: setSI. Qed.

Lemma setDS A B C : A \subset B -> C :\: B \subset C :\: A.
Proof. by rewrite !setDE -setCS; apply: setIS. Qed.

Lemma setDSS A B C D : A \subset C -> D \subset B -> A :\: B \subset C :\: D.
Proof. by move=> /(setSD B) /subset_trans sAC /(setDS C) /sAC. Qed.

Lemma setD0 A : A :\: set0 = A.
Proof. by apply/setP=> x; rewrite !inE. Qed.

Lemma set0D A : set0 :\: A = set0.
Proof. by apply/setP=> x; rewrite !inE andbF. Qed.

Lemma setDT A : A :\: setT = set0.
Proof. by apply/setP=> x; rewrite !inE. Qed.

Lemma setTD A : setT :\: A = ~: A.
Proof. by apply/setP=> x; rewrite !inE andbT. Qed.

Lemma setDv A : A :\: A = set0.
Proof. by apply/setP=> x; rewrite !inE andNb. Qed.

Lemma setCD A B : ~: (A :\: B) = ~: A :|: B.
Proof. by rewrite !setDE setCI setCK. Qed.

Lemma setID A B : A :&: B :|: A :\: B = A.
Proof. by rewrite setDE -setIUr setUCr setIT. Qed.

Lemma setDUl A B C : (A :|: B) :\: C = (A :\: C) :|: (B :\: C).
Proof. by rewrite !setDE setIUl. Qed.

Lemma setDUr A B C : A :\: (B :|: C) = (A :\: B) :&: (A :\: C).
Proof. by rewrite !setDE setCU setIIr. Qed.

Lemma setDIl A B C : (A :&: B) :\: C = (A :\: C) :&: (B :\: C).
Proof. by rewrite !setDE setIIl. Qed.

Lemma setIDA A B C : A :&: (B :\: C) = (A :&: B) :\: C.
Proof. by rewrite !setDE setIA. Qed.

Lemma setIDAC A B C : (A :\: B) :&: C = (A :&: C) :\: B.
Proof. by rewrite !setDE setIAC. Qed.

Lemma setDIr A B C : A :\: (B :&: C) = (A :\: B) :|: (A :\: C).
Proof. by rewrite !setDE setCI setIUr. Qed.

Lemma setDDl A B C : (A :\: B) :\: C = A :\: (B :|: C).
Proof. by rewrite !setDE setCU setIA. Qed.

Lemma setDDr A B C : A :\: (B :\: C) = (A :\: B) :|: (A :&: C).
Proof. by rewrite !setDE setCI setIUr setCK. Qed.

Lemma setUD B A C : B \subset A -> C \subset B ->
  (A :\: B) :|: (B :\: C) = (A :\: C).
Proof.
move=> subBA subCB; apply/setP=> x; rewrite !inE.
have /implyP  := subsetP subBA x; have /implyP  := subsetP subCB x.
by do !case: (_ \in _).
Qed.

Lemma setUDl A B: A :|: B :\: A = A :|: B.
Proof. by apply/setP=> x; rewrite !inE; do !case: (_ \in _). Qed.

(* powerset *)

Lemma powersetE A B : (A \in powerset B) = (A \subset B).
Proof. by rewrite inE. Qed.

Lemma powersetS A B : (powerset A \subset powerset B) = (A \subset B).
Proof.
apply/subsetP/idP=> [sAB | sAB C /[!inE]/subset_trans->//].
by rewrite -powersetE sAB // inE.
Qed.

Lemma powerset0 : powerset set0 = [set set0] :> {set {set T}}.
Proof. by apply/setP=> A; rewrite set1.unlock !inE subset0. Qed.

Lemma powersetT : powerset [set: T] = [set: {set T}].
Proof. by apply/setP=> A; rewrite !inE subsetT. Qed.

Lemma setI_powerset P A : P :&: powerset A = P ::&: A.
Proof. by apply/setP=> B; rewrite !inE. Qed.

(* cardinal lemmas for sets *)

Lemma cardsE pA : #|[set x in pA]| = #|pA|.
Proof. exact/eq_card/in_set. Qed.

Lemma sum1dep_card pA : \sum_(x | pA x) 1 = #|[set x | pA x]|.
Proof. by rewrite sum1_card cardsE. Qed.

Lemma sum_nat_cond_const pA n : \sum_(x | pA x) n = #|[set x | pA x]| * n.
Proof. by rewrite sum_nat_const cardsE. Qed.

Lemma cards0 : #|@set0 T| = 0.
Proof. by rewrite cardsE card0. Qed.

Lemma cards_eq0 A : (#|A| == 0) = (A == set0).
Proof. by rewrite (eq_sym A) eqEcard sub0set cards0 leqn0. Qed.

Lemma set0Pn A : reflect (exists x, x \in A) (A != set0).
Proof. by rewrite -cards_eq0; apply: existsP. Qed.

Lemma set0_Nexists A : (A == set0) = ~~ [exists x, x \in A].
Proof. by rewrite -(sameP (set0Pn _) existsP) negbK.  Qed.

Lemma card_gt0 A : (0 < #|A|) = (A != set0).
Proof. by rewrite lt0n cards_eq0. Qed.

Lemma cards0_eq A : #|A| = 0 -> A = set0.
Proof. by move=> A_0; apply/setP=> x; rewrite inE (card0_eq A_0). Qed.

Lemma cards1 x : #|[set x]| = 1.
Proof. by rewrite set1.unlock cardsE card1. Qed.

Lemma cardsUI A B : #|A :|: B| + #|A :&: B| = #|A| + #|B|.
Proof. by rewrite !cardsE cardUI. Qed.

Lemma cardsU A B : #|A :|: B| = #|A| + #|B| - #|A :&: B|.
Proof. by rewrite -cardsUI addnK. Qed.

Lemma cardsI A B : #|A :&: B| = #|A| + #|B| - #|A :|: B|.
Proof. by rewrite -cardsUI addKn. Qed.

Lemma cardsT : #|[set: T]| = #|T|.
Proof. by rewrite cardsE. Qed.

Lemma cardsID B A : #|A :&: B| + #|A :\: B| = #|A|.
Proof. by rewrite !cardsE cardID. Qed.

Lemma cardsD A B : #|A :\: B| = #|A| - #|A :&: B|.
Proof. by rewrite -(cardsID B A) addKn. Qed.

Lemma cardsC A : #|A| + #|~: A| = #|T|.
Proof. by rewrite cardsE cardC. Qed.

Lemma cardsCs A : #|A| = #|T| - #|~: A|.
Proof. by rewrite -(cardsC A) addnK. Qed.

Lemma cardsU1 a A : #|a |: A| = (a \notin A) + #|A|.
Proof. by rewrite -cardU1; apply: eq_card=> x; rewrite !inE. Qed.

Lemma cards2 a b : #|[set a; b]| = (a != b).+1.
Proof. by rewrite -card2; apply: eq_card=> x; rewrite !inE. Qed.

Lemma cardsC1 a : #|[set~ a]| = #|T|.-1.
Proof. by rewrite -(cardC1 a); apply: eq_card=> x; rewrite !inE. Qed.

Lemma cardsD1 a A : #|A| = (a \in A) + #|A :\ a|.
Proof.
by rewrite (cardD1 a); congr (_ + _); apply: eq_card => x; rewrite !inE.
Qed.

(* other inclusions *)

Lemma subsetIl A B : A :&: B \subset A.
Proof. by apply/subsetP=> x /[!inE] /andP[]. Qed.

Lemma subsetIr A B : A :&: B \subset B.
Proof. by apply/subsetP=> x /[!inE] /andP[]. Qed.

Lemma subsetUl A B : A \subset A :|: B.
Proof. by apply/subsetP=> x /[!inE] ->. Qed.

Lemma subsetUr A B : B \subset A :|: B.
Proof. by apply/subsetP=> x; rewrite inE orbC => ->. Qed.

Lemma subsetU1 x A : A \subset x |: A.
Proof. exact: subsetUr. Qed.

Lemma subsetDl A B : A :\: B \subset A.
Proof. by rewrite setDE subsetIl. Qed.

Lemma subD1set A x : A :\ x \subset A.
Proof. by rewrite subsetDl. Qed.

Lemma subsetDr A B : A :\: B \subset ~: B.
Proof. by rewrite setDE subsetIr. Qed.

Lemma sub1set A x : ([set x] \subset A) = (x \in A).
Proof. by rewrite -subset_pred1; apply: eq_subset=> y; rewrite !inE. Qed.

Variant cards_eq_spec A : seq T -> {set T} -> nat -> Type :=
| CardEq (s : seq T) & uniq s : cards_eq_spec A s [set x | x \in s] (size s).

Lemma cards_eqP A : cards_eq_spec A (enum A) A #|A|.
Proof.
by move: (enum A) (cardE A) (set_enum A) (enum_uniq A) => s -> <-; constructor.
Qed.

Lemma cards1P A : reflect (exists x, A = [set x]) (#|A| == 1).
Proof.
apply: (iffP idP) => [|[x ->]]; last by rewrite cards1.
by have [[|x []]// _] := cards_eqP; exists x; apply/setP => y; rewrite !inE.
Qed.

Lemma cards2P A : reflect (exists x y : T, x != y /\ A = [set x; y])
                          (#|A| == 2).
Proof.
apply: (iffP idP) => [|[x] [y] [xy ->]]; last by rewrite cards2 xy.
have [[|x [|y []]]//=] := cards_eqP; rewrite !inE andbT => neq_xy.
by exists x, y; split=> //; apply/setP => z; rewrite !inE.
Qed.

Lemma subset1 A x : (A \subset [set x]) = (A == [set x]) || (A == set0).
Proof.
rewrite eqEcard cards1 -cards_eq0 orbC andbC.
by case: posnP => // A0; rewrite (cards0_eq A0) sub0set.
Qed.

Lemma powerset1 x : powerset [set x] = [set set0; [set x]].
Proof. by apply/setP=> A; rewrite inE subset1 orbC set1.unlock !inE. Qed.

Lemma setIidPl A B : reflect (A :&: B = A) (A \subset B).
Proof.
apply: (iffP subsetP) => [sAB | <- x /setIP[] //].
by apply/setP=> x /[1!inE]; apply/andb_idr/sAB.
Qed.
Arguments setIidPl {A B}.

Lemma setIidPr A B : reflect (A :&: B = B) (B \subset A).
Proof. by rewrite setIC; apply: setIidPl. Qed.

Lemma cardsDS A B : B \subset A -> #|A :\: B| = #|A| - #|B|.
Proof. by rewrite cardsD => /setIidPr->. Qed.

Lemma setUidPl A B : reflect (A :|: B = A) (B \subset A).
Proof.
by rewrite -setCS (sameP setIidPl eqP) -setCU (inj_eq setC_inj); apply: eqP.
Qed.

Lemma setUidPr A B : reflect (A :|: B = B) (A \subset B).
Proof. by rewrite setUC; apply: setUidPl. Qed.

Lemma setDidPl A B : reflect (A :\: B = A) [disjoint A & B].
Proof. by rewrite setDE disjoints_subset; apply: setIidPl. Qed.

Lemma subIset A B C : (B \subset A) || (C \subset A) -> (B :&: C \subset A).
Proof. by case/orP; apply: subset_trans; rewrite (subsetIl, subsetIr). Qed.

Lemma subsetI A B C : (A \subset B :&: C) = (A \subset B) && (A \subset C).
Proof.
rewrite !(sameP setIidPl eqP) setIA; have [-> //|] := eqVneq (A :&: B) A.
by apply: contraNF => /eqP <-; rewrite -setIA -setIIl setIAC.
Qed.

Lemma subsetIP A B C : reflect (A \subset B /\ A \subset C) (A \subset B :&: C).
Proof. by rewrite subsetI; apply: andP. Qed.

Lemma subsetIidl A B : (A \subset A :&: B) = (A \subset B).
Proof. by rewrite subsetI subxx. Qed.

Lemma subsetIidr A B : (B \subset A :&: B) = (B \subset A).
Proof. by rewrite setIC subsetIidl. Qed.

Lemma powersetI A B : powerset (A :&: B) = powerset A :&: powerset B.
Proof. by apply/setP=> C; rewrite !inE subsetI. Qed.

Lemma subUset A B C : (B :|: C \subset A) = (B \subset A) && (C \subset A).
Proof. by rewrite -setCS setCU subsetI !setCS. Qed.

Lemma subsetU A B C : (A \subset B) || (A \subset C) -> A \subset B :|: C.
Proof. by rewrite -!(setCS _ A) setCU; apply: subIset. Qed.

Lemma subUsetP A B C : reflect (A \subset C /\ B \subset C) (A :|: B \subset C).
Proof. by rewrite subUset; apply: andP. Qed.

Lemma subsetC A B : (A \subset ~: B) = (B \subset ~: A).
Proof. by rewrite -setCS setCK. Qed.

Lemma subCset A B : (~: A \subset B) = (~: B \subset A).
Proof. by rewrite -setCS setCK. Qed.

Lemma subsetD A B C : (A \subset B :\: C) = (A \subset B) && [disjoint A & C].
Proof. by rewrite setDE subsetI -disjoints_subset. Qed.

Lemma subDset A B C : (A :\: B \subset C) = (A \subset B :|: C).
Proof.
apply/subsetP/subsetP=> sABC x; rewrite !inE.
  by case Bx: (x \in B) => // Ax; rewrite sABC ?inE ?Bx.
by case Bx: (x \in B) => // /sABC; rewrite inE Bx.
Qed.

Lemma subsetDP A B C :
  reflect (A \subset B /\ [disjoint A & C]) (A \subset B :\: C).
Proof. by rewrite subsetD; apply: andP. Qed.

Lemma setU_eq0 A B : (A :|: B == set0) = (A == set0) && (B == set0).
Proof. by rewrite -!subset0 subUset. Qed.

Lemma setD_eq0 A B : (A :\: B == set0) = (A \subset B).
Proof. by rewrite -subset0 subDset setU0. Qed.

Lemma setI_eq0 A B : (A :&: B == set0) = [disjoint A & B].
Proof. by rewrite disjoints_subset -setD_eq0 setDE setCK. Qed.

Lemma eq0_subset B A : (A == set0) = (A \subset B) && (A \subset ~: B).
Proof. by rewrite -subsetI setICr subset0. Qed.

Lemma disjoint_setI0 A B : [disjoint A & B] -> A :&: B = set0.
Proof. by rewrite -setI_eq0; move/eqP. Qed.

Lemma subsetC_disjoint A B : [disjoint A & B] ->
  forall C, C != set0 -> C \subset A -> ~~ (C \subset B).
Proof.
move=> dAB C + CA; apply: contra_neqN => CB.
by apply/eqP; rewrite -subset0 -(disjoint_setI0 dAB) subsetI CA CB.
Qed.

Lemma disjoints1 A x : [disjoint [set x] & A] = (x \notin A).
Proof. by rewrite (@eq_disjoint1 _ x) // => y; rewrite !inE. Qed.

Lemma subsetD1 A B x : (A \subset B :\ x) = (A \subset B) && (x \notin A).
Proof. by rewrite setDE subsetI subsetC sub1set inE. Qed.

Lemma subsetD1P A B x : reflect (A \subset B /\ x \notin A) (A \subset B :\ x).
Proof. by rewrite subsetD1; apply: andP. Qed.

Lemma properD1 A x : x \in A -> A :\ x \proper A.
Proof.
move=> Ax; rewrite properE subsetDl; apply/subsetPn; exists x=> //.
by rewrite in_setD1 Ax eqxx.
Qed.

Lemma properIr A B : ~~ (B \subset A) -> A :&: B \proper B.
Proof. by move=> nsAB; rewrite properE subsetIr subsetI negb_and nsAB. Qed.

Lemma properIl A B : ~~ (A \subset B) -> A :&: B \proper A.
Proof. by move=> nsBA; rewrite properE subsetIl subsetI negb_and nsBA orbT. Qed.

Lemma properUr A B : ~~ (A \subset B) ->  B \proper A :|: B.
Proof. by rewrite properE subsetUr subUset subxx /= andbT. Qed.

Lemma properUl A B : ~~ (B \subset A) ->  A \proper A :|: B.
Proof. by move=> not_sBA; rewrite setUC properUr. Qed.

Lemma proper1set A x : ([set x] \proper A) -> (x \in A).
Proof. by move/proper_sub; rewrite sub1set. Qed.

Lemma properIset A B C : (B \proper A) || (C \proper A) -> (B :&: C \proper A).
Proof. by case/orP; apply: sub_proper_trans; rewrite (subsetIl, subsetIr). Qed.

Lemma properI A B C : (A \proper B :&: C) -> (A \proper B) && (A \proper C).
Proof.
move=> pAI; apply/andP.
by split; apply: (proper_sub_trans pAI); rewrite (subsetIl, subsetIr).
Qed.

Lemma properU A B C : (B :|: C \proper A) -> (B \proper A) && (C \proper A).
Proof.
move=> pUA; apply/andP.
by split; apply: sub_proper_trans pUA; rewrite (subsetUr, subsetUl).
Qed.

Lemma properD A B C : (A \proper B :\: C) -> (A \proper B) && [disjoint A & C].
Proof. by rewrite setDE disjoints_subset => /properI/andP[-> /proper_sub]. Qed.

Lemma properCr A B : (A \proper ~: B) = (B \proper ~: A).
Proof. by rewrite -properC setCK. Qed.

Lemma properCl A B : (~: A \proper B) = (~: B \proper A).
Proof. by rewrite -properC setCK. Qed.

(* relationship with seq *)

Lemma enum_setU A B : perm_eq (enum (A :|: B)) (undup (enum A ++ enum B)).
Proof.
apply: uniq_perm; rewrite ?enum_uniq ?undup_uniq//.
by move=> i; rewrite mem_undup mem_enum inE mem_cat !mem_enum.
Qed.

Lemma enum_setI A B : perm_eq (enum (A :&: B)) (filter [in B] (enum A)).
Proof.
apply: uniq_perm; rewrite ?enum_uniq// 1?filter_uniq// ?enum_uniq//.
by move=> x; rewrite /= mem_enum mem_filter inE mem_enum andbC.
Qed.

Lemma has_set1 pA A a : has pA (enum [set a]) = pA a.
Proof. by rewrite enum_set1 has_seq1. Qed.

Lemma has_setU pA A B :
  has pA (enum (A :|: B)) = (has pA (enum A)) || (has pA (enum B)).
Proof. by rewrite (perm_has _ (enum_setU _ _)) has_undup has_cat. Qed.

Lemma all_set1 pA A a : all pA (enum [set a]) = pA a.
Proof. by rewrite enum_set1 all_seq1. Qed.

Lemma all_setU pA A B :
  all pA (enum (A :|: B)) = (all pA (enum A)) && (all pA (enum B)).
Proof. by rewrite (perm_all _ (enum_setU _ _)) all_undup all_cat. Qed.

End setOps.

Arguments set1P {T x a}.
Arguments set1_inj {T} [x1 x2].
Arguments set2P {T x a b}.
Arguments setIdP {T x pA pB}.
Arguments setIP {T x A B}.
Arguments setU1P {T x a B}.
Arguments setD1P {T x A b}.
Arguments setUP {T x A B}.
Arguments setDP {T A B x}.
Arguments cards1P {T A}.
Arguments setCP {T x A}.
Arguments setIidPl {T A B}.
Arguments setIidPr {T A B}.
Arguments setUidPl {T A B}.
Arguments setUidPr {T A B}.
Arguments setDidPl {T A B}.
Arguments subsetIP {T A B C}.
Arguments subUsetP {T A B C}.
Arguments subsetDP {T A B C}.
Arguments subsetD1P {T A B x}.
Prenex Implicits set1.
#[global] Hint Extern 0 (is_true (subset _ (mem (pred_of_set (setTfor _))))) =>
  solve [apply: subsetT_hint] : core.

Section setOpsAlgebra.

Import Monoid.

Variable T : finType.

HB.instance Definition _ := isComLaw.Build {set T} [set: T] (@setI T)
  (@setIA T) (@setIC T) (@setTI T).

HB.instance Definition _ := isMulLaw.Build {set T} set0 (@setI T)
  (@set0I T) (@setI0 T).

HB.instance Definition _ := isComLaw.Build {set T} set0 (@setU T)
  (@setUA T) (@setUC T) (@set0U T).

HB.instance Definition _ := isMulLaw.Build {set T} [set: T] (@setU T)
  (@setTU T) (@setUT T).

HB.instance Definition _ := isAddLaw.Build {set T} (@setU T) (@setI T)
  (@setUIl T) (@setUIr T).

HB.instance Definition _ := isAddLaw.Build {set T} (@setI T) (@setU T)
  (@setIUl T) (@setIUr T).

End setOpsAlgebra.

Section CartesianProd.

Variables fT1 fT2 : finType.
Variables (A1 : {set fT1}) (A2 : {set fT2}).

Definition setX := [set u | u.1 \in A1 & u.2 \in A2].

Lemma in_setX x1 x2 : ((x1, x2) \in setX) = (x1 \in A1) && (x2 \in A2).
Proof. by rewrite inE. Qed.

Lemma setXP x1 x2 : reflect (x1 \in A1 /\ x2 \in A2) ((x1, x2) \in setX).
Proof. by rewrite inE; apply: andP. Qed.

Lemma cardsX : #|setX| = #|A1| * #|A2|.
Proof. by rewrite cardsE cardX. Qed.

End CartesianProd.

Arguments setXP {fT1 fT2 A1 A2 x1 x2}.

Section CartesianNProd.

Variables (I : finType) (fT : I -> finType).
Variables (A : forall i, {set fT i}).
Implicit Types (x : {dffun forall i, fT i}).

Definition setXn := [set x : {dffun _} in family A].

Lemma in_setXn x : (x \in setXn) = [forall i, x i \in A i].
Proof. by rewrite inE. Qed.

Lemma setXnP x : reflect (forall i, x i \in A i) (x \in setXn).
Proof. by rewrite inE; apply: forallP. Qed.

Lemma cardsXn : #|setXn| = \prod_i #|A i|.
Proof. by rewrite cardsE card_family foldrE big_map big_enum. Qed.

End CartesianNProd.

Arguments setXnP {I fT A x}.

HB.lock
Definition imset (aT rT : finType) f mD := [set y in @image_mem aT rT f mD].
Canonical imset_unlock := Unlockable imset.unlock.

HB.lock
Definition imset2 (aT1 aT2 rT : finType) f (D1 : mem_pred aT1) (D2 : _ -> mem_pred aT2) :=
  [set y in @image_mem _ rT (uncurry f) (mem [pred u | D1 u.1 & D2 u.1 u.2])].
Canonical imset2_unlock := Unlockable imset2.unlock.

Definition preimset (aT : finType) rT f (R : mem_pred rT) :=
  [set x : aT | in_mem (f x) R].

Notation "f @^-1: A" := (preimset f (mem A)) (at level 24) : set_scope.
Notation "f @: A" := (imset f (mem A)) (at level 24) : set_scope.
Notation "f @2: ( A , B )" := (imset2 f (mem A) (fun _ => mem B))
  (at level 24, format "f  @2:  ( A ,  B )") : set_scope.

(* Comprehensions *)
Notation "[ 'set' E | x 'in' A ]" := ((fun x => E) @: A)
  (format "[ '[hv' 'set'  E '/ '  |  x  'in'  A ] ']'") : set_scope.
Notation "[ 'set' E | x 'in' A & P ]" := [set E | x in pred_of_set [set x in A | P]]
  (format "[ '[hv' 'set'  E '/ '  |  x  'in'  A '/ '  &  P ] ']'") : set_scope.
Notation "[ 'set' E | x 'in' A , y 'in' B ]" :=
  (imset2 (fun x y => E) (mem A) (fun x => mem B))
  (y at level 99, format
   "[ '[hv' 'set'  E '/ '  |  x  'in'  A , '/   '  y  'in'  B ] ']'"
  ) : set_scope.
Notation "[ 'set' E | x 'in' A , y 'in' B & P ]" :=
  [set E | x in A, y in pred_of_set [set y in B | P]]
  (format
   "[ '[hv' 'set'  E '/ '  |  x  'in'  A , '/   '  y  'in'  B '/ '  &  P ] ']'"
  ) : set_scope.

(* Typed variants *)
Notation "[ 'set' E | x : T 'in' A ]" := ((fun x : T => E) @: A)
  (only parsing) : set_scope.
Notation "[ 'set' E | x : T 'in' A & P ]" :=
  [set E | x : T in [set x : T in A | P]]
  (only parsing) : set_scope.
Notation "[ 'set' E | x : T 'in' A , y : U 'in' B ]" :=
  (imset2 (fun (x : T) (y : U) => E) (mem A) (fun (x : T) => mem B))
  (y at level 99, only parsing) : set_scope.
Notation "[ 'set' E | x : T 'in' A , y : U 'in' B & P ]" :=
  [set E | x : T in A, y : U in [set y : U in B | P]]
  (only parsing) : set_scope.

(* Comprehensions over a type *)
Local Notation predOfType T := (pred_of_simpl (@pred_of_argType T)).
Notation "[ 'set' E | x : T ]" := [set E | x : T in predOfType T]
  (format "[ '[hv' 'set'  E '/ '  |  x  :  T ] ']'") : set_scope.
Notation "[ 'set' E | x : T & P ]" :=
  [set E | x : T in pred_of_set [set x : T | P]]
  (format "[ '[hv' 'set'  E '/ '  |  x  :  T '/ '  &  P ] ']'") : set_scope.
Notation "[ 'set' E | x : T , y : U 'in' B ]" :=
  [set E | x : T in predOfType T, y : U in B]
  (y at level 99, format
   "[ '[hv' 'set'  E '/ '  |  x  :  T , '/   '  y  :  U  'in'  B ] ']'")
   : set_scope.
Notation "[ 'set' E | x : T , y : U 'in' B & P ]" :=
  [set E | x : T, y : U in pred_of_set [set y in B | P]]
  (format
 "[ '[hv ' 'set'  E '/'  |  x  :  T , '/  '  y  :  U  'in'  B '/'  &  P ] ']'"
  ) : set_scope.
Notation "[ 'set' E | x : T 'in' A , y : U ]" :=
  [set E | x : T in A, y : U in predOfType U]
  (format
   "[ '[hv' 'set'  E '/ '  |  x  :  T  'in'  A , '/   '  y  :  U ] ']'")
   : set_scope.
Notation "[ 'set' E | x : T 'in' A , y : U & P ]" :=
  [set E | x : T in A, y : U in pred_of_set [set y in P]]
  (format
   "[ '[hv' 'set'  E '/ '  |  x  :  T  'in'  A , '/   '  y  :  U  &  P ] ']'")
   : set_scope.
Notation "[ 'set' E | x : T , y : U ]" :=
  [set E | x : T, y : U in predOfType U]
  (format
   "[ '[hv' 'set'  E '/ '  |  x  :  T , '/   '  y  :  U ] ']'")
   : set_scope.
Notation "[ 'set' E | x : T , y : U & P ]" :=
  [set E | x : T, y : U in pred_of_set [set y in P]]
  (format
   "[ '[hv' 'set'  E '/ '  |  x  :  T , '/   '  y  :  U  &  P ] ']'")
   : set_scope.

(* Untyped variants *)
Notation "[ 'set' E | x , y 'in' B ]" := [set E | x : _, y : _ in B]
  (y at level 99, only parsing) : set_scope.
Notation "[ 'set' E | x , y 'in' B & P ]" := [set E | x : _, y : _ in B & P]
  (only parsing) : set_scope.
Notation "[ 'set' E | x 'in' A , y ]" := [set E | x : _ in A, y : _]
  (only parsing) : set_scope.
Notation "[ 'set' E | x 'in' A , y & P ]" := [set E | x : _ in A, y : _ & P]
  (only parsing) : set_scope.
Notation "[ 'set' E | x , y ]" := [set E | x : _, y : _]
  (only parsing) : set_scope.
Notation "[ 'set' E | x , y & P ]" := [set E | x : _, y : _ & P ]
  (only parsing) : set_scope.

Section FunImage.

Variables aT aT2 : finType.

Section ImsetTheory.

Variable rT : finType.

Section ImsetProp.

Variables (f : aT -> rT) (f2 : aT -> aT2 -> rT).

Lemma imsetP D y : reflect (exists2 x, in_mem x D & y = f x) (y \in imset f D).
Proof. by rewrite [@imset]unlock inE; apply: imageP. Qed.

Variant imset2_spec D1 D2 y : Prop :=
  Imset2spec x1 x2 of in_mem x1 D1 & in_mem x2 (D2 x1) & y = f2 x1 x2.

Lemma imset2P D1 D2 y : reflect (imset2_spec D1 D2 y) (y \in imset2 f2 D1 D2).
Proof.
rewrite [@imset2]unlock inE.
apply: (iffP imageP) => [[[x1 x2] Dx12] | [x1 x2 Dx1 Dx2]] -> {y}.
  by case/andP: Dx12; exists x1 x2.
by exists (x1, x2); rewrite //= !inE Dx1.
Qed.

Lemma imset_f (D : {pred aT}) x : x \in D -> f x \in f @: D.
Proof. by move=> Dx; apply/imsetP; exists x. Qed.

Lemma mem_imset (D : {pred aT}) x : injective f -> (f x \in f @: D) = (x \in D).
Proof.
by move=> f_inj; apply/imsetP/idP;[case=> [y] ? /f_inj -> | move=> ?; exists x].
Qed.

Lemma imset0 : f @: set0 = set0.
Proof. by apply/setP => y /[!inE]; apply/imsetP => -[x /[!inE]]. Qed.

Lemma imset_eq0 (A : {set aT}) : (f @: A == set0) = (A == set0).
Proof.
have [-> | [x Ax]] := set_0Vmem A; first by rewrite imset0 !eqxx.
by rewrite -!cards_eq0 (cardsD1 x) Ax (cardsD1 (f x)) imset_f.
Qed.

Lemma imset_set1 x : f @: [set x] = [set f x].
Proof.
apply/setP => y.
by apply/imsetP/set1P=> [[x' /set1P-> //]| ->]; exists x; rewrite ?set11.
Qed.

Lemma imset_inj : injective f -> injective (fun A : {set aT} => f @: A).
Proof.
move=> inj_f A B => /setP E; apply/setP => x.
by rewrite -(mem_imset A x inj_f) E mem_imset.
Qed.

Lemma imset_disjoint (A B : {pred aT}) :
  injective f -> [disjoint f @: A & f @: B] = [disjoint A & B].
Proof.
move=> inj_f; apply/pred0Pn/pred0Pn => /= [[_ /andP[/imsetP[x xA ->]] xB]|].
  by exists x; rewrite xA -(mem_imset B x inj_f).
by move=> [x /andP[xA xB]]; exists (f x); rewrite !mem_imset ?xA.
Qed.

Lemma imset2_f (D : {pred aT}) (D2 : aT -> {pred aT2}) x x2 :
    x \in D -> x2 \in D2 x ->
  f2 x x2 \in [set f2 y y2 | y in D, y2 in D2 y].
Proof. by move=> Dx Dx2; apply/imset2P; exists x x2. Qed.

Lemma mem_imset2 (D : {pred aT}) (D2 : aT -> {pred aT2}) x x2 :
    injective2 f2 ->
  (f2 x x2 \in [set f2 y y2 | y in D, y2 in D2 y])
    = (x \in D) && (x2 \in D2 x).
Proof.
move=> inj2_f; apply/imset2P/andP => [|[xD xD2]]; last by exists x x2.
by move => [x' x2' xD xD2 eq_f2]; case: (inj2_f _ _ _ _ eq_f2) => -> ->.
Qed.

Lemma sub_imset_pre (A : {pred aT}) (B : {pred rT}) :
  (f @: A \subset B) = (A \subset f @^-1: B).
Proof.
apply/subsetP/subsetP=> [sfAB x Ax | sAf'B fx].
  by rewrite inE sfAB ?imset_f.
by move=> /imsetP[a + ->] => /sAf'B /[!inE].
Qed.

Lemma preimsetS (A B : {pred rT}) :
  A \subset B -> (f @^-1: A) \subset (f @^-1: B).
Proof. by move=> sAB; apply/subsetP=> y /[!inE]; apply: subsetP. Qed.

Lemma preimset0 : f @^-1: set0 = set0.
Proof. by apply/setP=> x; rewrite !inE. Qed.

Lemma preimsetT : f @^-1: setT = setT.
Proof. by apply/setP=> x; rewrite !inE. Qed.

Lemma preimsetI (A B : {set rT}) :
  f @^-1: (A :&: B) = (f @^-1: A) :&: (f @^-1: B).
Proof. by apply/setP=> y; rewrite !inE. Qed.

Lemma preimsetU (A B : {set rT}) :
  f @^-1: (A :|: B) = (f @^-1: A) :|: (f @^-1: B).
Proof. by apply/setP=> y; rewrite !inE. Qed.

Lemma preimsetD (A B : {set rT}) :
  f @^-1: (A :\: B) = (f @^-1: A) :\: (f @^-1: B).
Proof. by apply/setP=> y; rewrite !inE. Qed.

Lemma preimsetC (A : {set rT}) : f @^-1: (~: A) = ~: f @^-1: A.
Proof. by apply/setP=> y; rewrite !inE. Qed.

Lemma imsetS (A B : {pred aT}) : A \subset B -> f @: A \subset f @: B.
Proof.
move=> sAB; apply/subsetP => _ /imsetP[x Ax ->].
by apply/imsetP; exists x; rewrite ?(subsetP sAB).
Qed.

Lemma imset_proper (A B : {set aT}) :
   {in B &, injective f} -> A \proper B -> f @: A \proper f @: B.
Proof.
move=> injf /properP[sAB [x Bx nAx]]; rewrite properE imsetS //=.
apply: contra nAx => sfBA.
have: f x \in f @: A by rewrite (subsetP sfBA) ?imset_f.
by case/imsetP=> y Ay /injf-> //; apply: subsetP sAB y Ay.
Qed.

Lemma preimset_proper (A B : {set rT}) :
  B \subset codom f -> A \proper B -> (f @^-1: A) \proper (f @^-1: B).
Proof.
move=> sBc /properP[sAB [u Bu nAu]]; rewrite properE preimsetS //=.
by apply/subsetPn; exists (iinv (subsetP sBc  _ Bu)); rewrite inE /= f_iinv.
Qed.

Lemma imsetU (A B : {set aT}) : f @: (A :|: B) = (f @: A) :|: (f @: B).
Proof.
apply/eqP; rewrite eqEsubset subUset.
rewrite 2?imsetS (andbT, subsetUl, subsetUr) // andbT.
apply/subsetP=> _ /imsetP[x ABx ->]; apply/setUP.
by case/setUP: ABx => [Ax | Bx]; [left | right]; apply/imsetP; exists x.
Qed.

Lemma imsetU1 a (A : {set aT}) : f @: (a |: A) = f a |: (f @: A).
Proof. by rewrite imsetU imset_set1. Qed.

Lemma imsetI (A B : {set aT}) :
  {in A & B, injective f} -> f @: (A :&: B) = f @: A :&: f @: B.
Proof.
move=> injf; apply/eqP; rewrite eqEsubset subsetI.
rewrite 2?imsetS (andTb, subsetIl, subsetIr) //=.
apply/subsetP=> _ /setIP[/imsetP[x Ax ->] /imsetP[z Bz /injf eqxz]].
by rewrite imset_f // inE Ax eqxz.
Qed.

Lemma imset2Sl (A B : {pred aT}) (C : {pred aT2}) :
  A \subset B -> f2 @2: (A, C) \subset f2 @2: (B, C).
Proof.
move=> sAB; apply/subsetP=> _ /imset2P[x y Ax Cy ->].
by apply/imset2P; exists x y; rewrite ?(subsetP sAB).
Qed.

Lemma imset2Sr (A B : {pred aT2}) (C : {pred aT}) :
  A \subset B -> f2 @2: (C, A) \subset f2 @2: (C, B).
Proof.
move=> sAB; apply/subsetP=> _ /imset2P[x y Ax Cy ->].
by apply/imset2P; exists x y; rewrite ?(subsetP sAB).
Qed.

Lemma imset2S (A B : {pred aT}) (A2 B2 : {pred aT2}) :
  A \subset B ->  A2 \subset B2 -> f2 @2: (A, A2) \subset f2 @2: (B, B2).
Proof.  by move=> /(imset2Sl B2) sBA /(imset2Sr A)/subset_trans->. Qed.

End ImsetProp.

Implicit Types (f g : aT -> rT) (D : {pred aT}) (R : {pred rT}).

Lemma eq_preimset f g R : f =1 g -> f @^-1: R = g @^-1: R.
Proof. by move=> eqfg; apply/setP => y; rewrite !inE eqfg. Qed.

Lemma eq_imset f g D : f =1 g -> f @: D = g @: D.
Proof.
move=> eqfg; apply/setP=> y.
by apply/imsetP/imsetP=> [] [x Dx ->]; exists x; rewrite ?eqfg.
Qed.

Lemma eq_in_imset f g D : {in D, f =1 g} -> f @: D = g @: D.
Proof.
move=> eqfg; apply/setP => y.
by apply/imsetP/imsetP=> [] [x Dx ->]; exists x; rewrite ?eqfg.
Qed.

Lemma eq_in_imset2 (f g : aT -> aT2 -> rT) (D : {pred aT}) (D2 : {pred aT2}) :
  {in D & D2, f =2 g} -> f @2: (D, D2) = g @2: (D, D2).
Proof.
move=> eqfg; apply/setP => y.
by apply/imset2P/imset2P=> [] [x x2 Dx Dx2 ->]; exists x x2; rewrite ?eqfg.
Qed.

End ImsetTheory.

Lemma imset2_pair (A : {set aT}) (B : {set aT2}) :
  [set (x, y) | x in A, y in B] = setX A B.
Proof.
apply/setP=> [[x y]]; rewrite !inE /=.
by apply/imset2P/andP=> [[_ _ _ _ [-> ->]//]| []]; exists x y.
Qed.

Lemma setXS (A1 B1 : {set aT}) (A2 B2 : {set aT2}) :
  A1 \subset B1 -> A2 \subset B2 -> setX A1 A2 \subset setX B1 B2.
Proof. by move=> sAB1 sAB2; rewrite -!imset2_pair imset2S. Qed.

End FunImage.

Arguments imsetP {aT rT f D y}.
Arguments imset2P {aT aT2 rT f2 D1 D2 y}.
Arguments imset_disjoint {aT rT f A B}.

Section unset1.
Variable (I : finType).
Implicit Types (i : I) (A : {set I}).

Lemma pick_set1 i0 : [pick x in [set i0]] = Some i0.
Proof. by case: pickP => [i /[!inE]/eqP-> | /(_ i0)/[!(inE, eqxx)]]. Qed.

Definition unset1 A : option I := if #|A| == 1 then [pick x in A] else None.

Lemma set1K : pcancel set1 unset1.
Proof. by move=> i; rewrite /unset1 cards1 eqxx pick_set1. Qed.

Lemma omap_unset1K A : #|A| = 1 -> omap set1 (unset1 A) = Some A.
Proof. by move=> /eqP/cards1P[i ->]; rewrite set1K. Qed.

Lemma unset10 : unset1 set0 = None. Proof. by rewrite /unset1 cards0. Qed.

Lemma unset1N1 A : #|A| != 1 -> unset1 A = None.
Proof. by move=> AN1; rewrite /unset1 ifN. Qed.

Lemma unset1K : ocancel unset1 set1.
Proof.
move=> A; rewrite /unset1.
by case: ifPn => // /cards1P[i ->]/=; rewrite pick_set1.
Qed.

End unset1.
Arguments unset1 {I}.

Lemma setXnS (I : finType) (T : I -> finType) (A B : forall i, {set T i}) :
  (forall i, A i \subset B i) -> setXn A \subset setXn B.
Proof.
move=> sAB; apply/subsetP => x /setXnP xA.
by apply/setXnP => i; apply/subsetP: (xA i).
Qed.

Lemma eq_setXn (I : finType) (T : I -> finType) (A B : forall i, {set T i}) :
  (forall i, A i = B i) -> setXn A = setXn B.
Proof.
by move=> eqAB; apply/eqP; rewrite eqEsubset !setXnS// => j; rewrite eqAB.
Qed.

Section BigOpsAnyOp.

Variables (R : Type) (x : R) (op : R -> R -> R).
Variables I : finType.
Implicit Type F : I -> R.

Lemma big_set0 F : \big[op/x]_(i in set0) F i = x.
Proof. by apply: big_pred0 => i; rewrite inE. Qed.

Lemma big_set1E j F : \big[op/x]_(i in [set j]) F i = op (F j) x.
Proof. by rewrite -big_pred1_eq_id; apply: eq_bigl => i; apply: in_set1. Qed.

Lemma big_set (A : pred I) F :
  \big[op/x]_(i in [set i | A i]) (F i) = \big[op/x]_(i in A) (F i).
Proof. by apply: eq_bigl => i; rewrite inE. Qed.

End BigOpsAnyOp.

Section BigOpsSemiGroup.

Variables (R : Type) (op : SemiGroup.com_law R).

Variable (le : rel R).
Hypotheses (le_refl : reflexive le) (le_incr : forall x y, le x (op x y)).

Context [x : R].

Lemma subset_le_big_cond (I : finType) (A A' P P' : {pred I}) (F : I -> R) :
    [set i in A | P i]  \subset [set i in A' | P' i] ->
  le (\big[op/x]_(i in A | P i) F i) (\big[op/x]_(i in A' | P' i) F i).
Proof.
by move=> /subsetP AP; apply: sub_le_big => // i; have /[!inE] := AP i.
Qed.

Lemma big_imset_idem [I J : finType] (h : I -> J) (A : pred I) F :
    idempotent_op op ->
  \big[op/x]_(j in h @: A) F j = \big[op/x]_(i in A) F (h i).
Proof.
rewrite -!big_image => op_idem; rewrite -big_undup// -[RHS]big_undup//.
apply/perm_big/perm_undup => j; apply/imageP.
have [mem_j | /imageP mem_j] := boolP (j \in [seq h j | j in A]).
- by exists j => //; apply/imsetP; apply: imageP mem_j.
- by case=> k /imsetP [i j_in_A ->] eq_i; apply: mem_j; exists i.
Qed.

End BigOpsSemiGroup.

Section BigOps.

Variables (R : Type) (idx : R).
Variables (op : Monoid.law idx) (aop : Monoid.com_law idx).
Variables (times : Monoid.mul_law idx) (plus : Monoid.add_law idx times).
Variables I J : finType.
Implicit Type A B : {set I}.
Implicit Type h : I -> J.
Implicit Type P : pred I.
Implicit Type F : I -> R.

Lemma big_set1 a F : \big[op/idx]_(i in [set a]) F i = F a.
Proof. by apply: big_pred1 => i; rewrite !inE. Qed.

Lemma big_setID A B F :
  \big[aop/idx]_(i in A) F i =
     aop (\big[aop/idx]_(i in A :&: B) F i)
         (\big[aop/idx]_(i in A :\: B) F i).
Proof.
rewrite (bigID [in B]) setDE.
by congr (aop _ _); apply: eq_bigl => i; rewrite !inE.
Qed.

Lemma big_setIDcond A B P F :
  \big[aop/idx]_(i in A | P i) F i =
     aop (\big[aop/idx]_(i in A :&: B | P i) F i)
         (\big[aop/idx]_(i in A :\: B | P i) F i).
Proof. by rewrite !big_mkcondr; apply: big_setID. Qed.

Lemma big_setD1 a A F : a \in A ->
  \big[aop/idx]_(i in A) F i = aop (F a) (\big[aop/idx]_(i in A :\ a) F i).
Proof.
move=> Aa; rewrite (bigD1 a Aa); congr (aop _).
by apply: eq_bigl => x; rewrite !inE andbC.
Qed.

Lemma big_setU1 a A F : a \notin A ->
  \big[aop/idx]_(i in a |: A) F i = aop (F a) (\big[aop/idx]_(i in A) F i).
Proof. by move=> notAa; rewrite (@big_setD1 a) ?setU11 //= setU1K. Qed.

Lemma big_subset_idem_cond A B P F :
    idempotent_op aop ->
    A \subset B ->
  aop (\big[aop/idx]_(i in A | P i) F i) (\big[aop/idx]_(i in B | P i) F i)
    = \big[aop/idx]_(i in B | P i) F i.
Proof.
by move=> idaop /setIidPr <-; rewrite (big_setIDcond B A) Monoid.mulmA /= idaop.
Qed.

Lemma big_subset_idem A B F :
    idempotent_op aop ->
    A \subset B ->
  aop (\big[aop/idx]_(i in A) F i) (\big[aop/idx]_(i in B) F i)
    = \big[aop/idx]_(i in B) F i.
Proof. by rewrite -2!big_condT; apply: big_subset_idem_cond. Qed.

Lemma big_setU_cond A B P F :
    idempotent_op aop ->
  \big[aop/idx]_(i in A :|: B | P i) F i
    = aop (\big[aop/idx]_(i in A | P i) F i) (\big[aop/idx]_(i in B | P i) F i).
Proof.
move=> idemaop; rewrite (big_setIDcond _ A) setUK setDUl setDv set0U.
rewrite (big_setIDcond B A) Monoid.mulmCA Monoid.mulmA /=.
by rewrite (@big_subset_idem_cond (B :&: A)) // subsetIr.
Qed.

Lemma big_setU A B F :
    idempotent_op aop ->
  \big[aop/idx]_(i in A :|: B) F i
    = aop (\big[aop/idx]_(i in A) F i) (\big[aop/idx]_(i in B) F i).
Proof. by rewrite -3!big_condT; apply: big_setU_cond. Qed.

Lemma big_imset h (A : {pred I}) G : {in A &, injective h} ->
  \big[aop/idx]_(j in h @: A) G j = \big[aop/idx]_(i in A) G (h i).
Proof.
move=> injh; pose hA := mem (image h A).
rewrite (eq_bigl hA) => [j|]; first exact/imsetP/imageP.
pose h' := omap (fun u : {j | hA j} => iinv (svalP u)) \o insub.
rewrite (reindex_omap h h') => [j hAj|]; rewrite {}/h'/= ?insubT/= ?f_iinv//.
apply: eq_bigl => i; case: insubP => [u /= -> def_u | nhAhi]; last first.
  by apply/andP/idP => [[]//| Ai]; case/imageP: nhAhi; exists i.
set i' := iinv _; have Ai' : i' \in A := mem_iinv (svalP u).
by apply/eqP/idP => [[<-] // | Ai]; congr Some; apply: injh; rewrite ?f_iinv.
Qed.

Lemma big_imset_cond h (A : {pred I}) (P : pred J) G : {in A &, injective h} ->
  \big[aop/idx]_(j in h @: A | P j) G j =
    \big[aop/idx]_(i in A | P (h i)) G (h i).
Proof. by move=> h_inj; rewrite 2!big_mkcondr big_imset. Qed.

Lemma partition_big_imset h (A : {pred I}) F :
  \big[aop/idx]_(i in A) F i =
     \big[aop/idx]_(j in h @: A) \big[aop/idx]_(i in A | h i == j) F i.
Proof. by apply: partition_big => i Ai; apply/imsetP; exists i. Qed.

Lemma big_cards1 (f : {set I} -> R) :
  \big[aop/idx]_(A : {set I} | #|A| == 1) f A
  = \big[aop/idx]_(i : I) f [set i].
Proof.
rewrite (reindex_omap set1 unset1) => [A /cards1P[i ->] /[!set1K]//|].
by apply: eq_bigl => i; rewrite set1K cards1 !eqxx.
Qed.

End BigOps.

Lemma bigA_distr (R : Type) (zero one : R) (mul : Monoid.mul_law zero)
  (add : Monoid.add_law zero mul) (I : finType) (F G : I -> R) :
  \big[mul/one]_i add (F i) (G i) =
  \big[add/zero]_(J in {set I}) \big[mul/one]_i (if i \in J then F i else G i).
Proof.
under eq_bigr => i _ do rewrite -(big_bool _ (fun b => if b then F i else G i)).
rewrite bigA_distr_bigA.
set f := fun J : {set I} => val J.
transitivity (\big[add/zero]_(f0 in (imset f (mem setT)))
                \big[mul/one]_i (if f0 i then F i else G i)).
  suff <-: setT = imset f (mem setT) by apply: congr_big=>// i; rewrite in_setT.
  apply/esym/eqP; rewrite -subTset; apply/subsetP => b _.
  by apply/imsetP; exists (FinSet b).
rewrite big_imset; first by case=> g; case=> h _ _; rewrite /f => /= ->.
apply: congr_big => //; case=> g; first exact: in_setT.
by move=> _; apply: eq_bigr => i _; congr (if _ then _ else _); rewrite unlock.
Qed.

Arguments big_setID [R idx aop I A].
Arguments big_setD1 [R idx aop I] a [A F].
Arguments big_setU1 [R idx aop I] a [A F].
Arguments big_imset [R idx aop I J h A].
Arguments partition_big_imset [R idx aop I J].

Section Fun2Set1.

Variables aT1 aT2 rT : finType.
Variables (f : aT1 -> aT2 -> rT).

Lemma imset2_set1l x1 (D2 : {pred aT2}) : f @2: ([set x1], D2) = f x1 @: D2.
Proof.
apply/setP=> y; apply/imset2P/imsetP=> [[x x2 /set1P->]| [x2 Dx2 ->]].
  by exists x2.
by exists x1 x2; rewrite ?set11.
Qed.

Lemma imset2_set1r x2 (D1 : {pred aT1}) : f @2: (D1, [set x2]) = f^~ x2 @: D1.
Proof.
apply/setP=> y; apply/imset2P/imsetP=> [[x1 x Dx1 /set1P->]| [x1 Dx1 ->]].
  by exists x1.
by exists x1 x2; rewrite ?set11.
Qed.

End Fun2Set1.

Section CardFunImage.

Variables aT aT2 rT : finType.
Variables (f : aT -> rT) (g : rT -> aT) (f2 : aT -> aT2 -> rT).
Variables (D : {pred aT}) (D2 : {pred aT}).

Lemma imset_card : #|f @: D| = #|image f D|.
Proof. by rewrite [@imset]unlock cardsE. Qed.

Lemma leq_imset_card : #|f @: D| <= #|D|.
Proof. by rewrite imset_card leq_image_card. Qed.

Lemma card_in_imset : {in D &, injective f} -> #|f @: D| = #|D|.
Proof. by move=> injf; rewrite imset_card card_in_image. Qed.

Lemma card_imset : injective f -> #|f @: D| = #|D|.
Proof. by move=> injf; rewrite imset_card card_image. Qed.

Lemma imset_injP : reflect {in D &, injective f} (#|f @: D| == #|D|).
Proof. by rewrite [@imset]unlock cardsE; apply: image_injP. Qed.

Lemma can2_in_imset_pre :
  {in D, cancel f g} -> {on D, cancel g & f} -> f @: D = g @^-1: D.
Proof.
move=> fK gK; apply/setP=> y; rewrite inE.
by apply/imsetP/idP=> [[x Ax ->] | Agy]; last exists (g y); rewrite ?(fK, gK).
Qed.

Lemma can2_imset_pre : cancel f g -> cancel g f -> f @: D = g @^-1: D.
Proof. by move=> fK gK; apply: can2_in_imset_pre; apply: in1W. Qed.

End CardFunImage.

Arguments imset_injP {aT rT f D}.

Lemma on_card_preimset (aT rT : finType) (f : aT -> rT) (R : {pred rT}) :
  {on R, bijective f} -> #|f @^-1: R| = #|R|.
Proof.
case=> g fK gK; rewrite -(can2_in_imset_pre gK) // card_in_imset //.
exact: can_in_inj gK.
Qed.

Lemma can_imset_pre (T : finType) f g (A : {set T}) :
  cancel f g -> f @: A = g @^-1: A :> {set T}.
Proof.
move=> fK; apply: can2_imset_pre => // x.
suffices fx: x \in codom f by rewrite -(f_iinv fx) fK.
exact/(subset_cardP (card_codom (can_inj fK)))/subsetP.
Qed.

Lemma imset_id (T : finType) (A : {set T}) : [set x | x in A] = A.
Proof. by apply/setP=> x; rewrite (@can_imset_pre _ _ id) ?inE. Qed.

Lemma card_preimset (T : finType) (f : T -> T) (A : {set T}) :
  injective f -> #|f @^-1: A| = #|A|.
Proof.
move=> injf; apply: on_card_preimset; apply: onW_bij.
have ontof: _ \in codom f by apply/(subset_cardP (card_codom injf))/subsetP.
by exists (fun x => iinv (ontof x)) => x; rewrite (f_iinv, iinv_f).
Qed.

Lemma card_powerset (T : finType) (A : {set T}) : #|powerset A| = 2 ^ #|A|.
Proof.
rewrite -card_bool -(card_pffun_on false) -(card_imset _ val_inj).
apply: eq_card => f; pose sf := false.-support f; pose D := finset sf.
have sDA: (D \subset A) = (sf \subset A) by apply: eq_subset; apply: in_set.
have eq_sf x : sf x = f x by rewrite /= negb_eqb addbF.
have valD: val D = f by rewrite /D unlock; apply/ffunP=> x; rewrite ffunE eq_sf.
apply/imsetP/pffun_onP=> [[B] | [sBA _]]; last by exists D; rewrite // inE ?sDA.
by rewrite inE -sDA -valD => sBA /val_inj->.
Qed.

Section FunImageComp.

Variables T T' U : finType.

Lemma imset_comp (f : T' -> U) (g : T -> T') (H : {pred T}) :
  (f \o g) @: H = f @: (g @: H).
Proof.
apply/setP/subset_eqP/andP.
split; apply/subsetP=> _ /imsetP[x0 Hx0 ->]; apply/imsetP.
  by exists (g x0); first apply: imset_f.
by move/imsetP: Hx0 => [x1 Hx1 ->]; exists x1.
Qed.

End FunImageComp.

Notation "\bigcup_ ( i <- r | P ) F" :=
  (\big[@setU _/set0]_(i <- r | P) F%SET) : set_scope.
Notation "\bigcup_ ( i <- r ) F" :=
  (\big[@setU _/set0]_(i <- r) F%SET) : set_scope.
Notation "\bigcup_ ( m <= i < n | P ) F" :=
  (\big[@setU _/set0]_(m <= i < n | P%B) F%SET) : set_scope.
Notation "\bigcup_ ( m <= i < n ) F" :=
  (\big[@setU _/set0]_(m <= i < n) F%SET) : set_scope.
Notation "\bigcup_ ( i | P ) F" :=
  (\big[@setU _/set0]_(i | P%B) F%SET) : set_scope.
Notation "\bigcup_ i F" :=
  (\big[@setU _/set0]_i F%SET) : set_scope.
Notation "\bigcup_ ( i : t | P ) F" :=
  (\big[@setU _/set0]_(i : t | P%B) F%SET) (only parsing): set_scope.
Notation "\bigcup_ ( i : t ) F" :=
  (\big[@setU _/set0]_(i : t) F%SET) (only parsing) : set_scope.
Notation "\bigcup_ ( i < n | P ) F" :=
  (\big[@setU _/set0]_(i < n | P%B) F%SET) : set_scope.
Notation "\bigcup_ ( i < n ) F" :=
  (\big[@setU _/set0]_ (i < n) F%SET) : set_scope.
Notation "\bigcup_ ( i 'in' A | P ) F" :=
  (\big[@setU _/set0]_(i in A | P%B) F%SET) : set_scope.
Notation "\bigcup_ ( i 'in' A ) F" :=
  (\big[@setU _/set0]_(i in A) F%SET) : set_scope.

Notation "\bigcap_ ( i <- r | P ) F" :=
  (\big[@setI _/setT]_(i <- r | P%B) F%SET) : set_scope.
Notation "\bigcap_ ( i <- r ) F" :=
  (\big[@setI _/setT]_(i <- r) F%SET) : set_scope.
Notation "\bigcap_ ( m <= i < n | P ) F" :=
  (\big[@setI _/setT]_(m <= i < n | P%B) F%SET) : set_scope.
Notation "\bigcap_ ( m <= i < n ) F" :=
  (\big[@setI _/setT]_(m <= i < n) F%SET) : set_scope.
Notation "\bigcap_ ( i | P ) F" :=
  (\big[@setI _/setT]_(i | P%B) F%SET) : set_scope.
Notation "\bigcap_ i F" :=
  (\big[@setI _/setT]_i F%SET) : set_scope.
Notation "\bigcap_ ( i : t | P ) F" :=
  (\big[@setI _/setT]_(i : t | P%B) F%SET) (only parsing): set_scope.
Notation "\bigcap_ ( i : t ) F" :=
  (\big[@setI _/setT]_(i : t) F%SET) (only parsing) : set_scope.
Notation "\bigcap_ ( i < n | P ) F" :=
  (\big[@setI _/setT]_(i < n | P%B) F%SET) : set_scope.
Notation "\bigcap_ ( i < n ) F" :=
  (\big[@setI _/setT]_(i < n) F%SET) : set_scope.
Notation "\bigcap_ ( i 'in' A | P ) F" :=
  (\big[@setI _/setT]_(i in A | P%B) F%SET) : set_scope.
Notation "\bigcap_ ( i 'in' A ) F" :=
  (\big[@setI _/setT]_(i in A) F%SET) : set_scope.

Section BigSetOps.

Variables T I : finType.
Implicit Types (U : {pred T}) (P : pred I) (A B : {set I}) (F :  I -> {set T}).

(* It is very hard to use this lemma, because the unification fails to *)
(* defer the F j pattern (even though it's a Miller pattern!).         *)
Lemma bigcup_sup j P F : P j -> F j \subset \bigcup_(i | P i) F i.
Proof. by move=> Pj; rewrite (bigD1 j) //= subsetUl. Qed.

Lemma bigcup_max j U P F :
  P j -> U \subset F j -> U \subset \bigcup_(i | P i) F i.
Proof. by move=> Pj sUF; apply: subset_trans (bigcup_sup _ Pj). Qed.

Lemma bigcupP x P F :
  reflect (exists2 i, P i & x \in F i) (x \in \bigcup_(i | P i) F i).
Proof.
apply: (iffP idP) => [|[i Pi]]; last first.
  by apply: subsetP x; apply: bigcup_sup.
by elim/big_rec: _ => [|i _ Pi _ /setUP[|//]]; [rewrite inE | exists i].
Qed.

Lemma bigcupsP U P F :
  reflect (forall i, P i -> F i \subset U) (\bigcup_(i | P i) F i \subset U).
Proof.
apply: (iffP idP) => [sFU i Pi| sFU].
  by apply: subset_trans sFU; apply: bigcup_sup.
by apply/subsetP=> x /bigcupP[i Pi]; apply: (subsetP (sFU i Pi)).
Qed.

Lemma bigcup0P P F :
  reflect (forall i, P i -> F i = set0) (\bigcup_(i | P i) F i == set0).
Proof.
rewrite -subset0; apply: (iffP (bigcupsP _ _ _)) => sub0 i /sub0; last by move->.
by rewrite subset0 => /eqP.
Qed.

Lemma bigcup_disjointP U P F  :
  reflect (forall i : I, P i -> [disjoint U & F i])
          [disjoint U & \bigcup_(i | P i) F i].
Proof.
apply: (iffP idP) => [dUF i Pp|dUF].
  by apply: disjointWr dUF; apply: bigcup_sup.
rewrite disjoint_sym disjoint_subset.
by apply/bigcupsP=> i /dUF; rewrite disjoint_sym disjoint_subset.
Qed.

Lemma bigcup_disjoint U P F :
  (forall i, P i -> [disjoint U & F i]) -> [disjoint U & \bigcup_(i | P i) F i].
Proof. by move/bigcup_disjointP. Qed.

Lemma bigcup_setU A B F :
  \bigcup_(i in A :|: B) F i =
     (\bigcup_(i in A) F i) :|: (\bigcup_ (i in B) F i).
Proof.
apply/setP=> x; apply/bigcupP/setUP=> [[i] | ].
  by case/setUP; [left | right]; apply/bigcupP; exists i.
by case=> /bigcupP[i Pi]; exists i; rewrite // inE Pi ?orbT.
Qed.

Lemma bigcup_seq r F : \bigcup_(i <- r) F i = \bigcup_(i in r) F i.
Proof.
elim: r => [|i r IHr]; first by rewrite big_nil big_pred0.
rewrite big_cons {}IHr; case r_i: (i \in r).
  rewrite (setUidPr _) ?bigcup_sup //.
  by apply: eq_bigl => j /[!inE]; case: eqP => // ->.
rewrite (bigD1 i (mem_head i r)) /=; congr (_ :|: _).
by apply: eq_bigl => j /=; rewrite andbC; case: eqP => // ->.
Qed.

(* Unlike its setU counterpart, this lemma is useable. *)
Lemma bigcap_inf j P F : P j -> \bigcap_(i | P i) F i \subset F j.
Proof. by move=> Pj; rewrite (bigD1 j) //= subsetIl. Qed.

Lemma bigcap_min j U P F :
  P j -> F j \subset U -> \bigcap_(i | P i) F i \subset U.
Proof. by move=> Pj; apply: subset_trans (bigcap_inf _ Pj). Qed.

Lemma bigcapsP U P F :
  reflect (forall i, P i -> U \subset F i) (U \subset \bigcap_(i | P i) F i).
Proof.
apply: (iffP idP) => [sUF i Pi | sUF].
  by apply: subset_trans sUF _; apply: bigcap_inf.
elim/big_rec: _ => [|i V Pi sUV]; apply/subsetP=> x Ux; rewrite inE //.
by rewrite !(subsetP _ x Ux) ?sUF.
Qed.

Lemma bigcapP x P F :
  reflect (forall i, P i -> x \in F i) (x \in \bigcap_(i | P i) F i).
Proof.
rewrite -sub1set.
by apply: (iffP (bigcapsP _ _ _)) => Fx i /Fx; rewrite sub1set.
Qed.

Lemma setC_bigcup J r (P : pred J) (F : J -> {set T}) :
  ~: (\bigcup_(j <- r | P j) F j) = \bigcap_(j <- r | P j) ~: F j.
Proof. by apply: big_morph => [A B|]; rewrite ?setC0 ?setCU. Qed.

Lemma setC_bigcap J r (P : pred J) (F : J -> {set T}) :
  ~: (\bigcap_(j <- r | P j) F j) = \bigcup_(j <- r | P j) ~: F j.
Proof. by apply: big_morph => [A B|]; rewrite ?setCT ?setCI. Qed.

Lemma bigcap_setU A B F :
  (\bigcap_(i in A :|: B) F i) =
    (\bigcap_(i in A) F i) :&: (\bigcap_(i in B) F i).
Proof. by apply: setC_inj; rewrite setCI !setC_bigcap bigcup_setU. Qed.

Lemma bigcap_seq r F : \bigcap_(i <- r) F i = \bigcap_(i in r) F i.
Proof. by apply: setC_inj; rewrite !setC_bigcap bigcup_seq. Qed.

End BigSetOps.

Arguments bigcup_sup [T I] j [P F].
Arguments bigcup_max [T I] j [U P F].
Arguments bigcupP {T I x P F}.
Arguments bigcupsP {T I U P F}.
Arguments bigcup_disjointP {T I U P F}.
Arguments bigcap_inf [T I] j [P F].
Arguments bigcap_min [T I] j [U P F].
Arguments bigcapP {T I x P F}.
Arguments bigcapsP {T I U P F}.

Section ImsetCurry.

Variables (aT1 aT2 rT : finType) (f : aT1 -> aT2 -> rT).

Section Curry.

Variables (A1 : {set aT1}) (A2 : {set aT2}).
Variables (D1 : {pred aT1}) (D2 : {pred aT2}).

Lemma curry_imset2X : f @2: (A1, A2) = uncurry f @: (setX A1 A2).
Proof.
rewrite [@imset]unlock unlock; apply/setP=> x; rewrite !in_set; congr (x \in _).
by apply: eq_image => u //=; rewrite !inE.
Qed.

Lemma curry_imset2l : f @2: (D1, D2) = \bigcup_(x1 in D1) f x1 @: D2.
Proof.
apply/setP=> y; apply/imset2P/bigcupP => [[x1 x2 Dx1 Dx2 ->{y}] | [x1 Dx1]].
  by exists x1; rewrite // imset_f.
by case/imsetP=> x2 Dx2 ->{y}; exists x1 x2.
Qed.

Lemma curry_imset2r : f @2: (D1, D2) = \bigcup_(x2 in D2) f^~ x2 @: D1.
Proof.
apply/setP=> y; apply/imset2P/bigcupP => [[x1 x2 Dx1 Dx2 ->{y}] | [x2 Dx2]].
  by exists x2; rewrite // (imset_f (f^~ x2)).
by case/imsetP=> x1 Dx1 ->{y}; exists x1 x2.
Qed.

End Curry.

Lemma imset2Ul (A B : {set aT1}) (C : {set aT2}) :
  f @2: (A :|: B, C) = f @2: (A, C) :|: f @2: (B, C).
Proof. by rewrite !curry_imset2l bigcup_setU. Qed.

Lemma imset2Ur (A : {set aT1}) (B C : {set aT2}) :
  f @2: (A, B :|: C) = f @2: (A, B) :|: f @2: (A, C).
Proof. by rewrite !curry_imset2r bigcup_setU. Qed.

End ImsetCurry.

Section Partitions.

Variables T I : finType.
Implicit Types (x y z : T) (A B D X : {set T}) (P Q : {set {set T}}).
Implicit Types (J : pred I) (F : I -> {set T}).

Definition cover P := \bigcup_(B in P) B.
Definition pblock P x := odflt set0 (pick [pred B in P | x \in B]).
Definition trivIset P := \sum_(B in P) #|B| == #|cover P|.
Definition partition P D := [&& cover P == D, trivIset P & set0 \notin P].

Definition is_transversal X P D :=
  [&& partition P D, X \subset D & [forall B in P, #|X :&: B| == 1]].
Definition transversal P D := [set odflt x [pick y in pblock P x] | x in D].
Definition transversal_repr x0 X B := odflt x0 [pick x in X :&: B].

Lemma leq_card_setU A B : #|A :|: B| <= #|A| + #|B| ?= iff [disjoint A & B].
Proof.
rewrite -(addn0 #|_|) -setI_eq0 -cards_eq0 -cardsUI eq_sym.
by rewrite (mono_leqif (leq_add2l _)).
Qed.

Lemma leq_card_cover P : #|cover P| <= \sum_(A in P) #|A| ?= iff trivIset P.
Proof.
split; last exact: eq_sym.
rewrite /cover; elim/big_rec2: _ => [|A n U _ leUn]; first by rewrite cards0.
by rewrite (leq_trans (leq_card_setU A U).1) ?leq_add2l.
Qed.

Lemma imset_cover (T' : finType) P  (f : T -> T') :
  [set f x | x in cover P] = \bigcup_(i in P) [set f x | x in i].
Proof.
apply/setP=> y; apply/imsetP/bigcupP => [|[A AP /imsetP[x xA ->]]].
  by move=> [x /bigcupP[A AP xA] ->]; exists A => //; rewrite imset_f.
by exists x => //; apply/bigcupP; exists A.
Qed.

Lemma cover1 A : cover [set A] = A.
Proof. by rewrite /cover big_set1. Qed.

Lemma subset_cover P P' : P \subset P' -> cover P \subset cover P'.
Proof.
move=> /subsetP subP; apply/subsetP=> x /bigcupP [scc /subP].
by move=> scc' x_in; apply/bigcupP; exists scc.
Qed.

Lemma trivIset1 A : trivIset [set A].
Proof. by rewrite /trivIset cover1 big_set1. Qed.

Lemma trivIsetP P :
  reflect {in P &, forall A B, A != B -> [disjoint A & B]} (trivIset P).
Proof.
rewrite -[P]set_enum; elim: {P}(enum _) (enum_uniq P) => [_ | A e IHe] /=.
  by rewrite /trivIset /cover !big_set0 cards0; left=> A; rewrite inE.
case/andP; rewrite set_cons -(in_set (fun B => B \in e)) => PA {}/IHe.
move: {e}[set x in e] PA => P PA IHP.
rewrite /trivIset /cover !big_setU1 //= eq_sym.
have:= leq_card_cover P; rewrite -(mono_leqif (leq_add2l #|A|)).
move/(leqif_trans (leq_card_setU _ _))->; rewrite disjoints_subset setC_bigcup.
case: bigcapsP => [disjA | meetA]; last first.
  right=> [tI]; case: meetA => B PB; rewrite -disjoints_subset.
  by rewrite tI ?setU11 ?setU1r //; apply: contraNneq PA => ->.
apply: (iffP IHP) => [] tI B C PB PC; last by apply: tI; apply: setU1r.
by case/setU1P: PC PB => [->|PC] /setU1P[->|PB]; try by [apply: tI | case/eqP];
  first rewrite disjoint_sym; rewrite disjoints_subset disjA.
Qed.

Lemma trivIsetS P Q : P \subset Q -> trivIset Q -> trivIset P.
Proof. by move/subsetP/sub_in2=> sPQ /trivIsetP/sPQ/trivIsetP. Qed.

Lemma trivIsetD P Q : trivIset P -> trivIset (P :\: Q).
Proof.
move/trivIsetP => tP; apply/trivIsetP => A B /setDP[TA _] /setDP[TB _]; exact: tP.
Qed.

Lemma trivIsetU P Q :
  trivIset Q -> trivIset P -> [disjoint cover Q & cover P] -> trivIset (Q :|: P).
Proof.
move => /trivIsetP tQ /trivIsetP tP dQP; apply/trivIsetP => A B.
move => /setUP[?|?] /setUP[?|?]; first [exact:tQ|exact:tP|move => _].
  by apply: disjointW dQP; rewrite bigcup_sup.
by rewrite disjoint_sym; apply: disjointW dQP; rewrite bigcup_sup.
Qed.

Lemma coverD1 P B : trivIset P -> B \in P -> cover (P :\ B) = cover P :\: B.
Proof.
move/trivIsetP => tP SP; apply/setP => x; rewrite inE.
apply/bigcupP/idP => [[A /setD1P [ADS AP] xA]|/andP[xNS /bigcupP[A AP xA]]].
  by rewrite (disjointFr (tP _ _ _ _ ADS)) //=; apply/bigcupP; exists A.
by exists A; rewrite // !inE AP andbT; apply: contraNneq xNS => <-.
Qed.

Lemma trivIsetI P D : trivIset P -> trivIset (P ::&: D).
Proof. by apply: trivIsetS; rewrite -setI_powerset subsetIl. Qed.

Lemma cover_setI P D : cover (P ::&: D) \subset cover P :&: D.
Proof.
by apply/bigcupsP=> A /setIdP[PA sAD]; rewrite subsetI sAD andbT (bigcup_max A).
Qed.

Lemma mem_pblock P x : (x \in pblock P x) = (x \in cover P).
Proof.
rewrite /pblock; apply/esym/bigcupP.
case: pickP => /= [A /andP[PA Ax]| noA]; first by rewrite Ax; exists A.
by rewrite inE => [[A PA Ax]]; case/andP: (noA A).
Qed.

Lemma pblock_mem P x : x \in cover P -> pblock P x \in P.
Proof.
by rewrite -mem_pblock /pblock; case: pickP => [A /andP[]| _] //=; rewrite inE.
Qed.

Lemma def_pblock P B x : trivIset P -> B \in P -> x \in B -> pblock P x = B.
Proof.
move/trivIsetP=> tiP PB Bx; have Px: x \in cover P by apply/bigcupP; exists B.
apply: (contraNeq (tiP _ _ _ PB)); first by rewrite pblock_mem.
by apply/pred0Pn; exists x; rewrite /= mem_pblock Px.
Qed.

Lemma same_pblock P x y :
  trivIset P -> x \in pblock P y -> pblock P x = pblock P y.
Proof.
rewrite {1 3}/pblock => tI; case: pickP => [A|]; last by rewrite inE.
by case/andP=> PA _{y} /= Ax; apply: def_pblock.
Qed.

Lemma eq_pblock P x y :
    trivIset P -> x \in cover P ->
  (pblock P x == pblock P y) = (y \in pblock P x).
Proof.
move=> tiP Px; apply/eqP/idP=> [eq_xy | /same_pblock-> //].
move: Px; rewrite -mem_pblock eq_xy /pblock.
by case: pickP => [B /andP[] // | _] /[1!inE].
Qed.

Lemma trivIsetU1 A P :
    {in P, forall B, [disjoint A & B]} -> trivIset P -> set0 \notin P ->
  trivIset (A |: P) /\ A \notin P.
Proof.
move=> tiAP tiP notPset0; split; last first.
  apply: contra notPset0 => P_A.
  by have:= tiAP A P_A; rewrite -setI_eq0 setIid => /eqP <-.
apply/trivIsetP=> B1 B2 /setU1P[->|PB1] /setU1P[->|PB2];
  by [apply: (trivIsetP _ tiP) | rewrite ?eqxx // ?(tiAP, disjoint_sym)].
Qed.

Lemma cover_imset J F : cover (F @: J) = \bigcup_(i in J) F i.
Proof.
apply/setP=> x.
apply/bigcupP/bigcupP=> [[_ /imsetP[i Ji ->]] | [i]]; first by exists i.
by exists (F i); first apply: imset_f.
Qed.

Lemma trivIimset J F (P := F @: J) :
    {in J &, forall i j, j != i -> [disjoint F i & F j]} -> set0 \notin P ->
  trivIset P /\ {in J &, injective F}.
Proof.
move=> tiF notPset0; split=> [|i j Ji Jj /= eqFij].
  apply/trivIsetP=> _ _ /imsetP[i Ji ->] /imsetP[j Jj ->] neqFij.
  by rewrite tiF // (contraNneq _ neqFij) // => ->.
apply: contraNeq notPset0 => neq_ij; apply/imsetP; exists i => //; apply/eqP.
by rewrite eq_sym -[F i]setIid setI_eq0 {1}eqFij tiF.
Qed.

Lemma cover_partition P D : partition P D -> cover P = D.
Proof. by case/and3P=> /eqP. Qed.

Lemma partition0 P D : partition P D -> (set0 \in P) = false.
Proof. case/and3P => _ _. by apply: contraNF. Qed.

Lemma partition_neq0 P D B : partition P D -> B \in P -> B != set0.
Proof. by move=> partP; apply: contraTneq => ->; rewrite (partition0 partP). Qed.

Lemma partition_trivIset P D : partition P D -> trivIset P.
Proof. by case/and3P. Qed.

Lemma partitionS P D B : partition P D -> B \in P -> B \subset D.
Proof.
by move=> partP BP; rewrite -(cover_partition partP); apply: bigcup_max BP _.
Qed.

Lemma partitionD1 P D B :
  partition P D -> B \in P -> partition (P :\ B) (D :\: B).
Proof.
case/and3P => /eqP covP trivP set0P SP.
by rewrite /partition inE (negbTE set0P) trivIsetD ?coverD1 -?covP ?eqxx ?andbF.
Qed.

Lemma partitionU1 P D B :
  partition P D -> B != set0 -> [disjoint B & D] -> partition (B |: P) (B :|: D).
Proof.
case/and3P => /eqP covP trivP set0P BD0 disSD.
rewrite /partition !inE (negbTE set0P) orbF [_ == B]eq_sym BD0 andbT.
rewrite /cover bigcup_setU /= big_set1 -covP eqxx /=.
by move: disSD; rewrite -covP => /bigcup_disjointP/trivIsetU1 => -[].
Qed.

Lemma partition_set0 P : partition P set0 = (P == set0).
Proof.
apply/and3P/eqP => [[/bigcup0P covP _ ]|->]; last first.
  by rewrite /partition inE /trivIset/cover !big_set0 cards0 !eqxx.
by apply: contraNeq => /set0Pn[B BP]; rewrite -(covP B BP).
Qed.

Lemma card_partition P D : partition P D -> #|D| = \sum_(A in P) #|A|.
Proof. by case/and3P=> /eqP <- /eqnP. Qed.

Lemma card_uniform_partition n P D :
  {in P, forall A, #|A| = n} -> partition P D -> #|D| = #|P| * n.
Proof.
by move=> uniP /card_partition->; rewrite -sum_nat_const; apply: eq_bigr.
Qed.

Lemma partition_pigeonhole P D A :
  partition P D -> #|P| <= #|A| -> A \subset D -> {in P, forall B, #|A :&: B| <= 1} ->
  {in P, forall B, A :&: B != set0}.
Proof.
move=> partP card_A_P /subsetP subAD sub1; apply/forall_inP.
apply: contraTT card_A_P => /forall_inPn [B BP]; rewrite negbK => AB0.
rewrite -!ltnNge -(setD1K BP) cardsU1 !inE eqxx /= add1n ltnS.
have [tP covP] := (partition_trivIset partP,cover_partition partP).
have APx x : x \in A -> x \in pblock P x by rewrite mem_pblock covP; apply: subAD.
have inj_f : {in A &, injective (pblock P)}.
  move=> x y xA yA /eqP; rewrite eq_pblock ?covP ?subAD // => Pxy.
  apply: (@card_le1_eqP _ (A :&: pblock P x)); rewrite ?inE ?Pxy ?APx ?andbT //.
  by apply: sub1; rewrite pblock_mem ?covP ?subAD.
rewrite -(card_in_imset inj_f); apply: subset_leq_card.
apply/subsetP => ? /imsetP[x xA ->].
rewrite !inE pblock_mem ?covP ?subAD ?andbT //.
by apply: contraTneq AB0 => <-; apply/set0Pn; exists x; rewrite inE APx ?andbT.
Qed.

Section BigOps.

Variables (R : Type) (idx : R) (op : Monoid.com_law idx).
Let rhs_cond P K E := \big[op/idx]_(A in P) \big[op/idx]_(x in A | K x) E x.
Let rhs P E := \big[op/idx]_(A in P) \big[op/idx]_(x in A) E x.

Lemma big_trivIset_cond P (K : pred T) (E : T -> R) :
  trivIset P -> \big[op/idx]_(x in cover P | K x) E x = rhs_cond P K E.
Proof.
move=> tiP; rewrite (partition_big (pblock P) [in P]) -/op => /= [x|].
  by case/andP=> Px _; apply: pblock_mem.
apply: eq_bigr => A PA; apply: eq_bigl => x; rewrite andbAC; congr (_ && _).
rewrite -mem_pblock; apply/andP/idP=> [[Px /eqP <- //] | Ax].
by rewrite (def_pblock tiP PA Ax).
Qed.

Lemma big_trivIset P (E : T -> R) :
  trivIset P -> \big[op/idx]_(x in cover P) E x = rhs P E.
Proof.
have biginT := eq_bigl _ _ (fun _ => andbT _) => tiP.
by rewrite -biginT big_trivIset_cond //; apply: eq_bigr => A _; apply: biginT.
Qed.

Lemma set_partition_big_cond P D (K : pred T) (E : T -> R) :
  partition P D -> \big[op/idx]_(x in D | K x) E x = rhs_cond P K E.
Proof. by case/and3P=> /eqP <- tI_P _; apply: big_trivIset_cond. Qed.

Lemma set_partition_big P D (E : T -> R) :
  partition P D -> \big[op/idx]_(x in D) E x = rhs P E.
Proof. by case/and3P=> /eqP <- tI_P _; apply: big_trivIset. Qed.

Lemma partition_disjoint_bigcup (F : I -> {set T}) E :
    (forall i j, i != j -> [disjoint F i & F j]) ->
  \big[op/idx]_(x in \bigcup_i F i) E x =
    \big[op/idx]_i \big[op/idx]_(x in F i) E x.
Proof.
move=> disjF; pose P := [set F i | i in I & F i != set0].
have trivP: trivIset P.
  apply/trivIsetP=> _ _ /imsetP[i _ ->] /imsetP[j _ ->] neqFij.
  by apply: disjF; apply: contraNneq neqFij => ->.
have ->: \bigcup_i F i = cover P.
  apply/esym; rewrite cover_imset big_mkcond; apply: eq_bigr => i _.
  by rewrite inE; case: eqP.
rewrite big_trivIset // /rhs big_imset => [i j _ /setIdP[_ notFj0] eqFij|].
  by apply: contraNeq (disjF _ _) _; rewrite -setI_eq0 eqFij setIid.
rewrite big_mkcond; apply: eq_bigr => i _; rewrite inE.
by case: eqP => //= ->; rewrite big_set0.
Qed.

End BigOps.

Section Equivalence.

Variables (R : rel T) (D : {set T}).

Let Px x := [set y in D | R x y].
Definition equivalence_partition := [set Px x | x in D].
Local Notation P := equivalence_partition.
Hypothesis eqiR : {in D & &, equivalence_rel R}.

Let Pxx x : x \in D -> x \in Px x.
Proof. by move=> Dx; rewrite !inE Dx (eqiR Dx Dx). Qed.
Let PPx x : x \in D -> Px x \in P := fun Dx => imset_f _ Dx.

Lemma equivalence_partitionP : partition P D.
Proof.
have defD: cover P == D.
  rewrite eqEsubset; apply/andP; split.
    by apply/bigcupsP=> _ /imsetP[x Dx ->]; rewrite /Px setIdE subsetIl.
  by apply/subsetP=> x Dx; apply/bigcupP; exists (Px x); rewrite (Pxx, PPx).
have tiP: trivIset P.
  apply/trivIsetP=> _ _ /imsetP[x Dx ->] /imsetP[y Dy ->]; apply: contraR.
  case/pred0Pn=> z /andP[] /[!inE] /andP[Dz Rxz] /andP[_ Ryz].
  apply/eqP/setP=> t /[!inE]; apply: andb_id2l => Dt.
  by rewrite (eqiR Dx Dz Dt) // (eqiR Dy Dz Dt).
rewrite /partition tiP defD /=.
by apply/imsetP=> [[x /Pxx Px_x Px0]]; rewrite -Px0 inE in Px_x.
Qed.

Lemma pblock_equivalence_partition :
  {in D &, forall x y, (y \in pblock P x) = R x y}.
Proof.
have [_ tiP _] := and3P equivalence_partitionP.
by move=> x y Dx Dy; rewrite /= (def_pblock tiP (PPx Dx) (Pxx Dx)) inE Dy.
Qed.

End Equivalence.

Lemma pblock_equivalence P D :
  partition P D -> {in D & &, equivalence_rel (fun x y => y \in pblock P x)}.
Proof.
case/and3P=> /eqP <- tiP _ x y z Px Py Pz.
by rewrite mem_pblock; split=> // /same_pblock->.
Qed.

Lemma equivalence_partition_pblock P D :
  partition P D -> equivalence_partition (fun x y => y \in pblock P x) D = P.
Proof.
case/and3P=> /eqP <-{D} tiP notP0; apply/setP=> B /=; set D := cover P.
have defP x: x \in D -> [set y in D | y \in pblock P x] = pblock P x.
  by move=> Dx; apply/setIidPr; rewrite (bigcup_max (pblock P x)) ?pblock_mem.
apply/imsetP/idP=> [[x Px ->{B}] | PB]; first by rewrite defP ?pblock_mem.
have /set0Pn[x Bx]: B != set0 := memPn notP0 B PB.
have Px: x \in cover P by apply/bigcupP; exists B.
by exists x; rewrite // defP // (def_pblock tiP PB Bx).
Qed.

Section Preim.

Variables (rT : eqType) (f : T -> rT).

Definition preim_partition := equivalence_partition (fun x y => f x == f y).

Lemma preim_partitionP D : partition (preim_partition D) D.
Proof. by apply/equivalence_partitionP; split=> // /eqP->. Qed.

End Preim.

Lemma preim_partition_pblock P D :
  partition P D -> preim_partition (pblock P) D = P.
Proof.
move=> partP; have [/eqP defD tiP _] := and3P partP.
rewrite -{2}(equivalence_partition_pblock partP); apply: eq_in_imset => x Dx.
by apply/setP=> y; rewrite !inE eq_pblock ?defD.
Qed.

Lemma transversalP P D : partition P D -> is_transversal (transversal P D) P D.
Proof.
case/and3P=> /eqP <- tiP notP0; apply/and3P; split; first exact/and3P.
  apply/subsetP=> _ /imsetP[x Px ->]; case: pickP => //= y Pxy.
  by apply/bigcupP; exists (pblock P x); rewrite ?pblock_mem //.
apply/forall_inP=> B PB; have /set0Pn[x Bx]: B != set0 := memPn notP0 B PB.
apply/cards1P; exists (odflt x [pick y in pblock P x]); apply/esym/eqP.
rewrite eqEsubset sub1set !inE -andbA; apply/andP; split.
  by apply/imset_f/bigcupP; exists B.
rewrite (def_pblock tiP PB Bx); case def_y: _ / pickP => [y By | /(_ x)/idP//].
rewrite By /=; apply/subsetP=> _ /setIP[/imsetP[z Pz ->]].
case: {1}_ / pickP => [t zPt Bt | /(_ z)/idP[]]; last by rewrite mem_pblock.
by rewrite -(same_pblock tiP zPt) (def_pblock tiP PB Bt) def_y inE.
Qed.

Section Transversals.

Variables (X : {set T}) (P : {set {set T}}) (D : {set T}).
Hypothesis trPX : is_transversal X P D.

Lemma transversal_sub : X \subset D. Proof. by case/and3P: trPX. Qed.

Let tiP : trivIset P. Proof. by case/andP: trPX => /and3P[]. Qed.

Let sXP : {subset X <= cover P}.
Proof. by case/and3P: trPX => /andP[/eqP-> _] /subsetP. Qed.

Let trX : {in P, forall B, #|X :&: B| == 1}.
Proof. by case/and3P: trPX => _ _ /forall_inP. Qed.

Lemma setI_transversal_pblock x0 B :
  B \in P -> X :&: B = [set transversal_repr x0 X B].
Proof.
by case/trX/cards1P=> x defXB; rewrite /transversal_repr defXB /pick enum_set1.
Qed.

Lemma repr_mem_pblock x0 B : B \in P -> transversal_repr x0 X B \in B.
Proof. by move=> PB; rewrite -sub1set -setI_transversal_pblock ?subsetIr. Qed.

Lemma repr_mem_transversal x0 B : B \in P -> transversal_repr x0 X B \in X.
Proof. by move=> PB; rewrite -sub1set -setI_transversal_pblock ?subsetIl. Qed.

Lemma transversal_reprK x0 : {in P, cancel (transversal_repr x0 X) (pblock P)}.
Proof. by move=> B PB; rewrite /= (def_pblock tiP PB) ?repr_mem_pblock. Qed.

Lemma pblockK x0 : {in X, cancel (pblock P) (transversal_repr x0 X)}.
Proof.
move=> x Xx; have /bigcupP[B PB Bx] := sXP Xx; rewrite (def_pblock tiP PB Bx).
by apply/esym/set1P; rewrite -setI_transversal_pblock // inE Xx.
Qed.

Lemma pblock_inj : {in X &, injective (pblock P)}.
Proof. by move=> x0; apply: (can_in_inj (pblockK x0)). Qed.

Lemma pblock_transversal : pblock P @: X = P.
Proof.
apply/setP=> B; apply/imsetP/idP=> [[x Xx ->] | PB].
  by rewrite pblock_mem ?sXP.
have /cards1P[x0 _] := trX PB; set x := transversal_repr x0 X B.
by exists x; rewrite ?transversal_reprK ?repr_mem_transversal.
Qed.

Lemma card_transversal : #|X| = #|P|.
Proof. by rewrite -pblock_transversal card_in_imset //; apply: pblock_inj. Qed.

Lemma im_transversal_repr x0 : transversal_repr x0 X @: P = X.
Proof.
rewrite -{2}[X]imset_id -pblock_transversal -imset_comp.
by apply: eq_in_imset; apply: pblockK.
Qed.

End Transversals.

End Partitions.

Arguments trivIsetP {T P}.
Arguments big_trivIset_cond [T R idx op] P [K E].
Arguments set_partition_big_cond [T R idx op] P [D K E].
Arguments big_trivIset [T R idx op] P [E].
Arguments set_partition_big [T R idx op] P [D E].

Prenex Implicits cover trivIset partition pblock.

Lemma partition_partition (T : finType) (D : {set T}) P Q :
    partition P D -> partition Q P ->
  partition (cover @: Q) D /\ {in Q &, injective cover}.
Proof.
move=> /and3P[/eqP defG tiP notP0] /and3P[/eqP defP tiQ notQ0].
have sQP E: E \in Q -> {subset E <= P}.
  by move=> Q_E; apply/subsetP; rewrite -defP (bigcup_max E).
rewrite /partition cover_imset -(big_trivIset _ tiQ) defP -defG eqxx /= andbC.
have{} notQ0: set0 \notin cover @: Q.
  apply: contra notP0 => /imsetP[E Q_E E0].
  have /set0Pn[/= A E_A] := memPn notQ0 E Q_E.
  congr (_ \in P): (sQP E Q_E A E_A).
  by apply/eqP; rewrite -subset0 E0 (bigcup_max A).
rewrite notQ0; apply: trivIimset => // E F Q_E Q_F.
apply: contraR => /pred0Pn[x /andP[/bigcupP[A E_A Ax] /bigcupP[B F_B Bx]]].
rewrite -(def_pblock tiQ Q_E E_A) -(def_pblock tiP _ Ax) ?(sQP E) //.
by rewrite -(def_pblock tiQ Q_F F_B) -(def_pblock tiP _ Bx) ?(sQP F).
Qed.

Lemma indexed_partition (I T : finType) (J : {pred I}) (B : I -> {set T}) :
  let P := [set B i | i in J] in
  {in J &, forall i j : I, j != i -> [disjoint B i & B j]} ->
  (forall i : I, J i -> B i != set0) -> partition P (cover P) /\ {in J &, injective B}.
Proof.
move=> P disjB inhB; have s0NP : set0 \notin P.
  by apply/negP => /imsetP[x xI /eqP]; apply/negP; rewrite eq_sym inhB.
by rewrite /partition eqxx s0NP andbT /=; apply: trivIimset.
Qed.

Section PartitionImage.
Variables (T : finType) (P : {set {set T}}) (D : {set T}).
Variables (T' : finType) (f : T -> T') (inj_f : injective f).
Let fP := [set f @: (B : {set T}) | B in P].

Lemma imset_trivIset : trivIset fP = trivIset P.
Proof.
apply/trivIsetP/trivIsetP => [trivP A B AP BP|].
- rewrite -(imset_disjoint inj_f) -(inj_eq (imset_inj inj_f)).
  by apply: trivP; rewrite imset_f.
- move=> trivP ? ? /imsetP[A AP ->] /imsetP[B BP ->].
  by rewrite (inj_eq (imset_inj inj_f)) imset_disjoint //; apply: trivP.
Qed.

Lemma imset0mem : (set0 \in fP) = (set0 \in P).
Proof.
apply/imsetP/idP => [[A AP /esym/eqP]|P0]; last by exists set0; rewrite ?imset0.
by rewrite imset_eq0 => /eqP<-.
Qed.

Lemma imset_partition : partition fP (f @: D) = partition P D.
Proof.
suff cov: (cover fP == f @:D) = (cover P == D).
  by rewrite /partition -imset_trivIset imset0mem cov.
by rewrite /fP cover_imset -imset_cover (inj_eq (imset_inj inj_f)).
Qed.
End PartitionImage.


(**********************************************************************)
(*                                                                    *)
(*  Maximum and minimum (sub)set with respect to a given pred         *)
(*                                                                    *)
(**********************************************************************)

Section MaxSetMinSet.

Variable T : finType.
Notation sT := {set T}.
Implicit Types A B C : sT.
Implicit Type P : pred sT.

Definition minset P A := [forall (B : sT | B \subset A), (B == A) == P B].

Lemma minset_eq P1 P2 A : P1 =1 P2 -> minset P1 A = minset P2 A.
Proof. by move=> eP12; apply: eq_forallb => B; rewrite eP12. Qed.

Lemma minsetP P A :
  reflect ((P A) /\ (forall B, P B -> B \subset A -> B = A)) (minset P A).
Proof.
apply: (iffP forallP) => [minA | [PA minA] B].
  split; first by have:= minA A; rewrite subxx eqxx /= => /eqP.
  by move=> B PB sBA; have:= minA B; rewrite PB sBA /= eqb_id => /eqP.
by apply/implyP=> sBA; apply/eqP; apply/eqP/idP=> [-> // | /minA]; apply.
Qed.
Arguments minsetP {P A}.

Lemma minsetp P A : minset P A -> P A.
Proof. by case/minsetP. Qed.

Lemma minsetinf P A B : minset P A -> P B -> B \subset A -> B = A.
Proof. by case/minsetP=> _; apply. Qed.

Lemma ex_minset P : (exists A, P A) -> {A | minset P A}.
Proof.
move=> exP; pose pS n := [pred B | P B & #|B| == n].
pose p n := ~~ pred0b (pS n); have{exP}: exists n, p n.
  by case: exP => A PA; exists #|A|; apply/existsP; exists A; rewrite /= PA /=.
case/ex_minnP=> n /pred0P; case: (pickP (pS n)) => // A /andP[PA] /eqP <-{n} _.
move=> minA; exists A => //; apply/minsetP; split=> // B PB sBA; apply/eqP.
by rewrite eqEcard sBA minA //; apply/pred0Pn; exists B; rewrite /= PB /=.
Qed.

Lemma minset_exists P C : P C -> {A | minset P A & A \subset C}.
Proof.
move=> PC; have{PC}: exists A, P A && (A \subset C) by exists C; rewrite PC /=.
case/ex_minset=> A /minsetP[/andP[PA sAC] minA]; exists A => //; apply/minsetP.
by split=> // B PB sBA; rewrite (minA B) // PB (subset_trans sBA).
Qed.

(* The 'locked_with' allows Coq to find the value of P by unification. *)
Fact maxset_key : unit. Proof. by []. Qed.
Definition maxset P A :=
  minset (fun B => locked_with maxset_key P (~: B)) (~: A).

Lemma maxset_eq P1 P2 A : P1 =1 P2 -> maxset P1 A = maxset P2 A.
Proof. by move=> eP12; apply: minset_eq => x /=; rewrite !unlock_with eP12. Qed.

Lemma maxminset P A : maxset P A = minset [pred B | P (~: B)] (~: A).
Proof. by rewrite /maxset unlock. Qed.

Lemma minmaxset P A : minset P A = maxset [pred B | P (~: B)] (~: A).
Proof.
by rewrite /maxset unlock setCK; apply: minset_eq => B /=; rewrite setCK.
Qed.

Lemma maxsetP P A :
  reflect ((P A) /\ (forall B, P B -> A \subset B -> B = A)) (maxset P A).
Proof.
apply: (iffP minsetP); rewrite ?setCK unlock_with => [] [PA minA].
  by split=> // B PB sAB; rewrite -[B]setCK [~: B]minA (setCK, setCS).
by split=> // B PB' sBA'; rewrite -(minA _ PB') -1?setCS setCK.
Qed.

Lemma maxsetp P A : maxset P A -> P A.
Proof. by case/maxsetP. Qed.

Lemma maxsetsup P A B : maxset P A -> P B -> A \subset B -> B = A.
Proof. by case/maxsetP=> _; apply. Qed.

Lemma ex_maxset P : (exists A, P A) -> {A | maxset P A}.
Proof.
move=> exP; have{exP}: exists A, P (~: A).
  by case: exP => A PA; exists (~: A); rewrite setCK.
by case/ex_minset=> A minA; exists (~: A); rewrite /maxset unlock setCK.
Qed.

Lemma maxset_exists P C : P C -> {A : sT | maxset P A & C \subset A}.
Proof.
move=> PC; pose P' B := P (~: B); have: P' (~: C) by rewrite /P' setCK.
case/minset_exists=> B; rewrite -[B]setCK setCS.
by exists (~: B); rewrite // /maxset unlock.
Qed.

End MaxSetMinSet.

Arguments setCK {T}.
Arguments minsetP {T P A}.
Arguments maxsetP {T P A}.
Prenex Implicits minset maxset.

Section SetFixpoint.

Section Least.
Variables (T : finType) (F : {set T} -> {set T}).
Hypothesis (F_mono : {homo F : X Y / X \subset Y}).

Let n := #|T|.
Let iterF i := iter i F set0.

Lemma subset_iterS i : iterF i \subset iterF i.+1.
Proof. by elim: i => [| i IHi]; rewrite /= ?sub0set ?F_mono. Qed.

Lemma subset_iter : {homo iterF : i j / i <= j >-> i \subset j}.
Proof.
by apply: homo_leq => //[? ? ?|]; [apply: subset_trans|apply: subset_iterS].
Qed.

Definition fixset := iterF n.

Lemma fixsetK : F fixset = fixset.
Proof.
suff /'exists_eqP[x /= e]: [exists k : 'I_n.+1, iterF k == iterF k.+1].
  by rewrite /fixset -(subnK (leq_ord x)) /iterF iterD iter_fix.
apply: contraT => /existsPn /(_ (Ordinal _)) /= neq_iter.
suff iter_big k : k <= n.+1 -> k <= #|iter k F set0|.
  by have := iter_big _ (leqnn _); rewrite ltnNge max_card.
elim: k => [|k IHk] k_lt //=; apply: (leq_ltn_trans (IHk (ltnW k_lt))).
by rewrite proper_card// properEneq// subset_iterS neq_iter.
Qed.
Hint Resolve fixsetK : core.

Lemma minset_fix : minset [pred X | F X == X] fixset.
Proof.
apply/minsetP; rewrite inE fixsetK eqxx; split=> // X /eqP FXeqX Xsubfix.
apply/eqP; rewrite eqEsubset Xsubfix/=.
suff: fixset \subset iter n F X by rewrite iter_fix.
by rewrite /fixset; elim: n => //= [|m IHm]; rewrite ?sub0set ?F_mono.
Qed.

Lemma fixsetKn k : iter k F fixset = fixset.
Proof. by rewrite iter_fix. Qed.

Lemma iter_sub_fix k : iterF k \subset fixset.
Proof.
have [/subset_iter //|/ltnW/subnK<-] := leqP k n;
by rewrite /iterF iterD fixsetKn.
Qed.

Lemma fix_order_proof x : x \in fixset -> exists n, x \in iterF n.
Proof. by move=> x_fix; exists n. Qed.

Definition fix_order (x : T) :=
 if (x \in fixset) =P true isn't ReflectT x_fix then 0
 else (ex_minn (fix_order_proof x_fix)).

Lemma fix_order_le_max (x : T) : fix_order x <= n.
Proof.
rewrite /fix_order; case: eqP => //= x_in.
by case: ex_minnP => //= ? ?; apply.
Qed.

Lemma in_iter_fix_orderE (x : T) :
  (x \in iterF (fix_order x)) = (x \in fixset).
Proof.
rewrite /fix_order; case: eqP => [x_in | /negP/negPf-> /[1!inE]//].
by case: ex_minnP => m ->; rewrite x_in.
Qed.

Lemma fix_order_gt0 (x : T) : (fix_order x > 0) = (x \in fixset).
Proof.
rewrite /fix_order; case: eqP => [x_in | /negP/negPf->//].
by rewrite x_in; case: ex_minnP => -[/[!inE] | m].
Qed.

Lemma fix_order_eq0 (x : T) : (fix_order x == 0) = (x \notin fixset).
Proof. by rewrite -fix_order_gt0 -ltnNge ltnS leqn0. Qed.

Lemma in_iter_fixE (x : T) k : (x \in iterF k) = (0 < fix_order x <= k).
Proof.
rewrite /fix_order; case: eqP => //= [x_in|/negP xNin]; last first.
  by apply: contraNF xNin; apply/subsetP/iter_sub_fix.
case: ex_minnP => -[/[!inE]//|m] xm mP.
by apply/idP/idP=> [/mP//|lt_mk]; apply: subsetP xm; apply: subset_iter.
Qed.

Lemma in_iter (x : T) k : x \in fixset -> fix_order x <= k -> x \in iterF k.
Proof. by move=> x_in xk; rewrite in_iter_fixE fix_order_gt0 x_in xk. Qed.

Lemma notin_iter (x : T) k : k < fix_order x -> x \notin iterF k.
Proof. by move=> k_le; rewrite in_iter_fixE negb_and orbC -ltnNge k_le. Qed.

Lemma fix_order_small x k : x \in iterF k -> fix_order x <= k.
Proof. by rewrite in_iter_fixE => /andP[]. Qed.

Lemma fix_order_big x k : x \in fixset -> x \notin iterF k -> fix_order x > k.
Proof. by move=> x_in; rewrite in_iter_fixE fix_order_gt0 x_in /= -ltnNge. Qed.

Lemma le_fix_order (x y : T) : y \in iterF (fix_order x) ->
  fix_order y <= fix_order x.
Proof. exact: fix_order_small. Qed.

End Least.

Section Greatest.
Variables (T : finType) (F : {set T} -> {set T}).
Hypothesis (F_mono : {homo F : X Y / X \subset Y}).

Definition funsetC X := ~: (F (~: X)).
Lemma funsetC_mono : {homo funsetC : X Y / X \subset Y}.
Proof. by move=> *; rewrite subCset setCK F_mono// subCset setCK. Qed.
Hint Resolve funsetC_mono : core.

Definition cofixset := ~: fixset funsetC.

Lemma cofixsetK : F cofixset = cofixset.
Proof. by rewrite /cofixset -[in RHS]fixsetK ?setCK. Qed.

Lemma maxset_cofix : maxset [pred X | F X == X] cofixset.
Proof.
rewrite maxminset setCK.
rewrite (@minset_eq _ _ [pred X | funsetC X == X]) ?minset_fix//.
by move=> X /=; rewrite (can2_eq setCK setCK).
Qed.

End Greatest.

End SetFixpoint.

Section FProd.

Variables (I : finType) (T_ : I -> finType).

Lemma card_fprod : #|fprod T_| = \prod_(i : I) #|T_ i|.
Proof.
rewrite card_sub (card_family (tagged_with T_)) foldrE big_image/=.
apply: eq_bigr => i _/=; rewrite -card_sig; apply/esym.
exact: bij_eq_card (tag_with_bij T_ i).
Qed.

Definition fprod_pick : 0 < #|fprod T_| -> forall i : I, T_ i.
Proof.
by rewrite card_fprod => /[swap] i /gt0_prodn/(_ i isT) /card_gt0P/sigW[].
Qed.

Definition ftagged (T_gt0 : 0 < #|fprod T_|)
  (f : {ffun I -> {i : I & T_ i}}) (i : I) :=
    @untag I T_ (T_ i) (fprod_pick T_gt0 i) i id (f i).

Lemma ftaggedE t T_gt0 i : ftagged T_gt0 (fprod_fun t) i = t i.
Proof. by rewrite /ftagged untagE ?tag_fprod_fun// => e; rewrite etaggedE. Qed.

End FProd.

Section BigTag.
Variables (R : Type) (idx : R) (op : Monoid.com_law idx).
Variables (I : finType) (T_ : I -> finType).

Lemma big_tag_cond  (Q_ : forall i, {pred T_ i})
      (P_ : forall i : I, T_ i -> R) (i : I) :
  \big[op/idx]_(j in Q_ i) P_ i j =
  \big[op/idx]_(j in tagged_with T_ i | untag true (Q_ i) j)
     untag idx (P_ i) j.
Proof.
rewrite (big_sub_cond (tagged_with T_ i)).
rewrite (reindex (tag_with i)); first exact/onW_bij/tag_with_bij.
by apply: eq_big => [x|x Qix]; rewrite ?untagE.
Qed.

Lemma big_tag (P_ : forall i : I, T_ i -> R) (i : I) :
  \big[op/idx]_(j : T_ i) P_ i j =
  \big[op/idx]_(j in tagged_with T_ i) untag idx (P_ i) j.
Proof. by rewrite big_tag_cond; under eq_bigl do rewrite untag_cst ?andbT. Qed.

End BigTag.

Arguments big_tag_cond [R idx op I T_] _ _ _.
Arguments big_tag [R idx op I T_] _ _.

Section BigFProd.
  Variables (R : Type) (zero one : R) (times : R -> R -> R).
  Variables (plus : Monoid.add_law zero times).
  Variables (I : finType) (T_ : I -> finType).
  Variables (P_ : forall i : I, {ffun T_ i -> R}).
  Let T := fprod T_.

  Lemma big_fprod_dep (Q : {pred {ffun I -> {i : I &  (T_ i)}}}) :
    \big[plus/zero]_(t : T | Q (fprod_fun t)) \big[times/one]_(i : I) P_ i (t i) =
    \big[plus/zero]_(g in family (tagged_with T_) | Q g)
     \big[times/one]_(i : I) (untag zero (P_ i) (g i)).
  Proof.
  rewrite (reindex (@of_family_tagged_with _ T_)).
    exact/onW_bij/of_family_tagged_with_bij.
  rewrite [in RHS]big_sub_cond; apply/esym/eq_bigr => -[/= f fP] Qf.
  apply: eq_bigr => i _; rewrite /fun_of_fprod/=.
  by case: (f i) ('forall_eqP _ _) => //= j t; case: _ /; rewrite untagE.
  Qed.

  Lemma big_fprod :
    \big[plus/zero]_(t : T) \big[times/one]_(i in I) P_ i (t i) =
    \big[plus/zero]_(g in family (tagged_with T_))
     \big[times/one]_(i : I) (untag zero (P_ i) (g i)).
  Proof. by rewrite (big_fprod_dep predT) big_mkcondr. Qed.

End BigFProd.