A model of ZFC

In this file, we model Zermelo-Fraenkel set theory (+ Choice) using Lean's underlying type theory. We do this in four main steps:

• Define pre-sets inductively.
• Define extensional equivalence on pre-sets and give it a setoid instance.
• Define ZFC sets by quotienting pre-sets by extensional equivalence.
• Define classes as sets of ZFC sets. Then the rest is usual set theory.

The model

• PSet: Pre-set. A pre-set is inductively defined by its indexing type and its members, which are themselves pre-sets.
• ZFSet: ZFC set. Defined as PSet quotiented by PSet.Equiv, the extensional equivalence.
• Class: Class. Defined as Set ZFSet.
• ZFSet.choice: Axiom of choice. Proved from Lean's axiom of choice.

Other definitions

• PSet.Type: Underlying type of a pre-set.
• PSet.Func: Underlying family of pre-sets of a pre-set.
• PSet.Equiv: Extensional equivalence of pre-sets. Defined inductively.
• PSet.omega, ZFSet.omega: The von Neumann ordinal ω as a PSet, as a Set.
• PSet.Arity.Equiv: Extensional equivalence of n-ary PSet-valued functions. Extension of PSet.Equiv.
• PSet.Resp: Collection of n-ary PSet-valued functions that respect extensional equivalence.
• PSet.eval: Turns a PSet-valued function that respect extensional equivalence into a ZFSet-valued function.
• Classical.allDefinable: All functions are classically definable.
• ZFSet.IsFunc : Predicate that a ZFC set is a subset of x × y that can be considered as a ZFC function x → y. That is, each member of x is related by the ZFC set to exactly one member of y.
• ZFSet.funs: ZFC set of ZFC functions x → y.
• ZFSet.Hereditarily p x: Predicate that every set in the transitive closure of x has property p.
• Class.iota: Definite description operator.

Notes

To avoid confusion between the Lean Set and the ZFC Set, docstrings in this file refer to them respectively as "Set" and "ZFC set".

TODO

Prove ZFSet.mapDefinableAux computably.

inductive PSet : Type (u + 1)

The type of pre-sets in universe u. A pre-set is a family of pre-sets indexed by a type in Type u. The ZFC universe is defined as a quotient of this to ensure extensionality.

• mk: (α : Type u) → (α → PSet) → PSet

def PSet.Type : PSet → Type u

The underlying type of a pre-set

Equations

• x.Type = match x with | PSet.mk α A => α

def PSet.Func (x : PSet) : x.Type → PSet

The underlying pre-set family of a pre-set

Equations

• x.Func = match (motive := (x : PSet) → x.Type → PSet) x with | PSet.mk α A => A

@[simp]

theorem PSet.mk_type (α : Type u_1) (A : α → PSet) : (PSet.mk α A).Type = α

@[simp]

theorem PSet.mk_func (α : Type u_1) (A : α → PSet) : (PSet.mk α A).Func = A

@[simp]

theorem PSet.eta (x : PSet) : PSet.mk x.Type x.Func = x

def PSet.Equiv : PSet → PSet → Prop

Two pre-sets are extensionally equivalent if every element of the first family is extensionally equivalent to some element of the second family and vice-versa.

Equations

• (PSet.mk α A).Equiv (PSet.mk α_1 B) = ((∀ (a : α), ∃ (b : α_1), (A a).Equiv (B b)) ∧ ∀ (b : α_1), ∃ (a : α), (A a).Equiv (B b))

theorem PSet.equiv_iff {x : PSet} {y : PSet} : x.Equiv y ↔ (∀ (i : x.Type), ∃ (j : y.Type), (x.Func i).Equiv (y.Func j)) ∧ ∀ (j : y.Type), ∃ (i : x.Type), (x.Func i).Equiv (y.Func j)

theorem PSet.Equiv.exists_left {x : PSet} {y : PSet} (h : x.Equiv y) (i : x.Type) : ∃ (j : y.Type), (x.Func i).Equiv (y.Func j)

theorem PSet.Equiv.exists_right {x : PSet} {y : PSet} (h : x.Equiv y) (j : y.Type) : ∃ (i : x.Type), (x.Func i).Equiv (y.Func j)

theorem PSet.Equiv.refl (x : PSet) : x.Equiv x

theorem PSet.Equiv.rfl {x : PSet} : x.Equiv x

theorem PSet.Equiv.euc {x : PSet} {y : PSet} {z : PSet} : x.Equiv y → z.Equiv y → x.Equiv z

theorem PSet.Equiv.symm {x : PSet} {y : PSet} : x.Equiv y → y.Equiv x

theorem PSet.Equiv.comm {x : PSet} {y : PSet} : x.Equiv y ↔ y.Equiv x

theorem PSet.Equiv.trans {x : PSet} {y : PSet} {z : PSet} (h1 : x.Equiv y) (h2 : y.Equiv z) : x.Equiv z

theorem PSet.equiv_of_isEmpty (x : PSet) (y : PSet) [IsEmpty x.Type] [IsEmpty y.Type] : x.Equiv y

instance PSet.setoid : Setoid PSet

Equations

• PSet.setoid = { r := PSet.Equiv, iseqv := PSet.setoid.proof_1 }

def PSet.Subset (x : PSet) (y : PSet) : Prop

A pre-set is a subset of another pre-set if every element of the first family is extensionally equivalent to some element of the second family.

Equations

• x.Subset y = ∀ (a : x.Type), ∃ (b : y.Type), (x.Func a).Equiv (y.Func b)

instance PSet.instHasSubset : HasSubset PSet

Equations

• PSet.instHasSubset = { Subset := PSet.Subset }

instance PSet.instIsReflSubset : IsRefl PSet fun (x x_1 : PSet) => x ⊆ x_1

Equations

• PSet.instIsReflSubset = ⋯

instance PSet.instIsTransSubset : IsTrans PSet fun (x x_1 : PSet) => x ⊆ x_1

Equations

• PSet.instIsTransSubset = ⋯

theorem PSet.Equiv.ext (x : PSet) (y : PSet) : x.Equiv y ↔ x ⊆ y ∧ y ⊆ x

theorem PSet.Subset.congr_left {x : PSet} {y : PSet} {z : PSet} : x.Equiv y → (x ⊆ z ↔ y ⊆ z)

theorem PSet.Subset.congr_right {x : PSet} {y : PSet} {z : PSet} : x.Equiv y → (z ⊆ x ↔ z ⊆ y)

def PSet.Mem (x : PSet) (y : PSet) : Prop

x ∈ y as pre-sets if x is extensionally equivalent to a member of the family y.

Equations

• x.Mem y = ∃ (b : y.Type), x.Equiv (y.Func b)

instance PSet.instMembership : Membership PSet PSet

Equations

• PSet.instMembership = { mem := PSet.Mem }

theorem PSet.Mem.mk {α : Type u} (A : α → PSet) (a : α) : A a ∈ PSet.mk α A

theorem PSet.func_mem (x : PSet) (i : x.Type) : x.Func i ∈ x

theorem PSet.Mem.ext {x : PSet} {y : PSet} : (∀ (w : PSet), w ∈ x ↔ w ∈ y) → x.Equiv y

theorem PSet.Mem.congr_right {x : PSet} {y : PSet} : x.Equiv y → ∀ {w : PSet}, w ∈ x ↔ w ∈ y

theorem PSet.equiv_iff_mem {x : PSet} {y : PSet} : x.Equiv y ↔ ∀ {w : PSet}, w ∈ x ↔ w ∈ y

theorem PSet.Mem.congr_left {x : PSet} {y : PSet} : x.Equiv y → ∀ {w : PSet}, x ∈ w ↔ y ∈ w

theorem PSet.mem_wf : WellFounded fun (x x_1 : PSet) => x ∈ x_1

instance PSet.instWellFoundedRelation : WellFoundedRelation PSet

Equations

• PSet.instWellFoundedRelation = { rel := fun (x x_1 : PSet) => x ∈ x_1, wf := PSet.mem_wf }

instance PSet.instIsAsymmMem : IsAsymm PSet fun (x x_1 : PSet) => x ∈ x_1

Equations

• PSet.instIsAsymmMem = ⋯

instance PSet.instIsIrreflMem : IsIrrefl PSet fun (x x_1 : PSet) => x ∈ x_1

Equations

• PSet.instIsIrreflMem = ⋯

theorem PSet.mem_asymm {x : PSet} {y : PSet} : x ∈ y → y ∉ x

theorem PSet.mem_irrefl (x : PSet) : x ∉ x

def PSet.toSet (u : PSet) : Set PSet

Convert a pre-set to a Set of pre-sets.

Equations

• u.toSet = {x : PSet | x ∈ u}

@[simp]

theorem PSet.mem_toSet (a : PSet) (u : PSet) : a ∈ u.toSet ↔ a ∈ u

def PSet.Nonempty (u : PSet) : Prop

A nonempty set is one that contains some element.

Equations

• u.Nonempty = u.toSet.Nonempty

theorem PSet.nonempty_def (u : PSet) : u.Nonempty ↔ ∃ (x : PSet), x ∈ u

theorem PSet.nonempty_of_mem {x : PSet} {u : PSet} (h : x ∈ u) : u.Nonempty

@[simp]

theorem PSet.nonempty_toSet_iff {u : PSet} : u.toSet.Nonempty ↔ u.Nonempty

theorem PSet.nonempty_type_iff_nonempty {x : PSet} : Nonempty x.Type ↔ x.Nonempty

theorem PSet.nonempty_of_nonempty_type (x : PSet) [h : Nonempty x.Type] : x.Nonempty

theorem PSet.Equiv.eq {x : PSet} {y : PSet} : x.Equiv y ↔ x.toSet = y.toSet

Two pre-sets are equivalent iff they have the same members.

instance PSet.instCoeSet : Coe PSet (Set PSet)

Equations

• PSet.instCoeSet = { coe := PSet.toSet }

def PSet.empty : PSet

The empty pre-set

Equations

• PSet.empty = PSet.mk PEmpty.{u_1 + 1} PEmpty.elim

instance PSet.instEmptyCollection : EmptyCollection PSet

Equations

• PSet.instEmptyCollection = { emptyCollection := PSet.empty }

instance PSet.instInhabited : Inhabited PSet

Equations

• PSet.instInhabited = { default := ∅ }

instance PSet.instIsEmptyTypeEmptyCollection : IsEmpty ∅.Type

Equations

• PSet.instIsEmptyTypeEmptyCollection = ⋯

@[simp]

theorem PSet.not_mem_empty (x : PSet) : x ∉ ∅

@[simp]

theorem PSet.toSet_empty : ∅.toSet = ∅

@[simp]

theorem PSet.empty_subset (x : PSet) : ∅ ⊆ x

@[simp]

theorem PSet.not_nonempty_empty : ¬∅.Nonempty

theorem PSet.equiv_empty (x : PSet) [IsEmpty x.Type] : x.Equiv ∅

def PSet.insert (x : PSet) (y : PSet) : PSet

Insert an element into a pre-set

Equations

• x.insert y = PSet.mk (Option y.Type) fun (o : Option y.Type) => Option.casesOn o x y.Func

instance PSet.instInsert : Insert PSet PSet

Equations

• PSet.instInsert = { insert := PSet.insert }

instance PSet.instSingleton : Singleton PSet PSet

Equations

• PSet.instSingleton = { singleton := fun (s : PSet) => insert s ∅ }

instance PSet.instLawfulSingleton : LawfulSingleton PSet PSet

Equations

• PSet.instLawfulSingleton = ⋯

instance PSet.instInhabitedTypeInsert (x : PSet) (y : PSet) : Inhabited (insert x y).Type

Equations

• x.instInhabitedTypeInsert y = inferInstanceAs (Inhabited (Option y.Type))

def PSet.ofNat : ℕ → PSet

The n-th von Neumann ordinal

Equations

• PSet.ofNat 0 = ∅
• PSet.ofNat n.succ = insert (PSet.ofNat n) (PSet.ofNat n)

def PSet.omega : PSet

The von Neumann ordinal ω

Equations

• PSet.omega = PSet.mk (ULift.{u_1, 0} ℕ) fun (n : ULift.{u_1, 0} ℕ) => PSet.ofNat n.down

def PSet.sep (p : PSet → Prop) (x : PSet) : PSet

The pre-set separation operation {x ∈ a | p x}

Equations

• PSet.sep p x = PSet.mk { a : x.Type // p (x.Func a) } fun (y : { a : x.Type // p (x.Func a) }) => x.Func ↑y

instance PSet.instSep : Sep PSet PSet

Equations

• PSet.instSep = { sep := PSet.sep }

def PSet.powerset (x : PSet) : PSet

The pre-set powerset operator

Equations

• x.powerset = PSet.mk (Set x.Type) fun (p : Set x.Type) => PSet.mk { a : x.Type // p a } fun (y : { a : x.Type // p a }) => x.Func ↑y

@[simp]

theorem PSet.mem_powerset {x : PSet} {y : PSet} : y ∈ x.powerset ↔ y ⊆ x

def PSet.sUnion (a : PSet) : PSet

The pre-set union operator

Equations

• ⋃₀ a = PSet.mk ((x : a.Type) × (a.Func x).Type) fun (x : (x : a.Type) × (a.Func x).Type) => match x with | ⟨x, y⟩ => (a.Func x).Func y

def PSet.«term⋃₀_» : Lean.ParserDescr

The pre-set union operator

Equations

• PSet.«term⋃₀_» = Lean.ParserDescr.node `PSet.term⋃₀_ 110 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol "⋃₀ ") (Lean.ParserDescr.cat `term 110))

@[simp]

theorem PSet.mem_sUnion {x : PSet} {y : PSet} : y ∈ ⋃₀ x ↔ ∃ z ∈ x, y ∈ z

@[simp]

theorem PSet.toSet_sUnion (x : PSet) : (⋃₀ x).toSet = ⋃₀ (PSet.toSet '' x.toSet)

def PSet.image (f : PSet → PSet) (x : PSet) : PSet

The image of a function from pre-sets to pre-sets.

Equations

• PSet.image f x = PSet.mk x.Type (f ∘ x.Func)

theorem PSet.mem_image {f : PSet → PSet} (H : ∀ (x y : PSet), x.Equiv y → (f x).Equiv (f y)) {x : PSet} {y : PSet} : y ∈ PSet.image f x ↔ ∃ z ∈ x, y.Equiv (f z)

def PSet.Lift : PSet → PSet

Universe lift operation

Equations

• (PSet.mk α A).Lift = PSet.mk (ULift.{?u.131, ?u.132} α) fun (x : ULift.{?u.131, ?u.132} α) => match x with | { down := x } => (A x).Lift

def PSet.embed : PSet

Embedding of one universe in another

Equations

• PSet.embed = PSet.mk (ULift.{v, u + 1} PSet) fun (x : ULift.{v, u + 1} PSet) => match x with | { down := x } => x.Lift

theorem PSet.lift_mem_embed (x : PSet) : x.Lift ∈ PSet.embed

def PSet.Arity.Equiv {n : ℕ} : Function.OfArity PSet PSet n → Function.OfArity PSet PSet n → Prop

Function equivalence is defined so that f ~ g iff ∀ x y, x ~ y → f x ~ g y. This extends to equivalence of n-ary functions.

Equations

• PSet.Arity.Equiv a b = PSet.Equiv a b
• PSet.Arity.Equiv a b = ∀ (x y : PSet), x.Equiv y → PSet.Arity.Equiv (a x) (b y)

theorem PSet.Arity.equiv_const {a : PSet} (n : ℕ) : PSet.Arity.Equiv (Function.OfArity.const PSet a n) (Function.OfArity.const PSet a n)

def PSet.Resp (n : ℕ) : Type (u + 1)

resp n is the collection of n-ary functions on PSet that respect equivalence, i.e. when the inputs are equivalent the output is as well.

Equations

• PSet.Resp n = { x : Function.OfArity PSet PSet n // PSet.Arity.Equiv x x }

instance PSet.Resp.inhabited {n : ℕ} : Inhabited (PSet.Resp n)

Equations

• PSet.Resp.inhabited = { default := ⟨Function.OfArity.const PSet default n, ⋯⟩ }

def PSet.Resp.f {n : ℕ} (f : PSet.Resp (n + 1)) (x : PSet) : PSet.Resp n

The n-ary image of a (n + 1)-ary function respecting equivalence as a function respecting equivalence.

Equations

• f.f x = ⟨↑f x, ⋯⟩

def PSet.Resp.Equiv {n : ℕ} (a : PSet.Resp n) (b : PSet.Resp n) : Prop

Function equivalence for functions respecting equivalence. See PSet.Arity.Equiv.

Equations

• a.Equiv b = PSet.Arity.Equiv ↑a ↑b

theorem PSet.Resp.Equiv.refl {n : ℕ} (a : PSet.Resp n) : a.Equiv a

theorem PSet.Resp.Equiv.euc {n : ℕ} {a : PSet.Resp n} {b : PSet.Resp n} {c : PSet.Resp n} : a.Equiv b → c.Equiv b → a.Equiv c

theorem PSet.Resp.Equiv.symm {n : ℕ} {a : PSet.Resp n} {b : PSet.Resp n} : a.Equiv b → b.Equiv a

theorem PSet.Resp.Equiv.trans {n : ℕ} {x : PSet.Resp n} {y : PSet.Resp n} {z : PSet.Resp n} (h1 : x.Equiv y) (h2 : y.Equiv z) : x.Equiv z

instance PSet.Resp.setoid {n : ℕ} : Setoid (PSet.Resp n)

Equations

• PSet.Resp.setoid = { r := PSet.Resp.Equiv, iseqv := ⋯ }

def ZFSet : Type (u + 1)

The ZFC universe of sets consists of the type of pre-sets, quotiented by extensional equivalence.

Equations

• ZFSet = Quotient PSet.setoid

def PSet.Resp.evalAux {n : ℕ} : { f : PSet.Resp n → Function.OfArity ZFSet ZFSet n // ∀ (a b : PSet.Resp n), a.Equiv b → f a = f b }

Helper function for PSet.eval.

Equations

• PSet.Resp.evalAux = ⟨fun (a : PSet.Resp 0) => ⟦↑a⟧, PSet.Resp.evalAux.proof_4⟩
• PSet.Resp.evalAux = let F := fun (a : PSet.Resp (n + 1)) => Quotient.lift (fun (x : PSet) => ↑PSet.Resp.evalAux (a.f x)) ⋯; ⟨F, ⋯⟩

def PSet.Resp.eval (n : ℕ) : PSet.Resp n → Function.OfArity ZFSet ZFSet n

An equivalence-respecting function yields an n-ary ZFC set function.

Equations

• PSet.Resp.eval n = ↑PSet.Resp.evalAux

theorem PSet.Resp.eval_val {n : ℕ} {f : PSet.Resp (n + 1)} {x : PSet} : PSet.Resp.eval (n + 1) f ⟦x⟧ = PSet.Resp.eval n (f.f x)

class inductive PSet.Definable (n : ℕ) : Function.OfArity ZFSet ZFSet n → Type (u + 1)

A set function is "definable" if it is the image of some n-ary pre-set function. This isn't exactly definability, but is useful as a sufficient condition for functions that have a computable image.

• mk: {n : ℕ} → (f : PSet.Resp n) → PSet.Definable n (PSet.Resp.eval n f)

def PSet.Definable.EqMk {n : ℕ} (f : PSet.Resp n) {s : Function.OfArity ZFSet ZFSet n} : PSet.Resp.eval n f = s → PSet.Definable n s

The evaluation of a function respecting equivalence is definable, by that same function.

Equations

• PSet.Definable.EqMk f x = match x✝, x with | .(PSet.Resp.eval n f), ⋯ => PSet.Definable.mk f

def PSet.Definable.Resp {n : ℕ} (s : Function.OfArity ZFSet ZFSet n) [PSet.Definable n s] : PSet.Resp n

Turns a definable function into a function that respects equivalence.

Equations

• PSet.Definable.Resp x✝ = match x✝, x with | .(PSet.Resp.eval n f), PSet.Definable.mk f => f

theorem PSet.Definable.eq {n : ℕ} (s : Function.OfArity ZFSet ZFSet n) [H : PSet.Definable n s] : PSet.Resp.eval n (PSet.Definable.Resp s) = s

noncomputable def Classical.allDefinable {n : ℕ} (F : Function.OfArity ZFSet ZFSet n) : PSet.Definable n F

All functions are classically definable.

Equations

• Classical.allDefinable F = let p := ⋯; PSet.Definable.EqMk ⟨Classical.choose p, ⋯⟩ ⋯
• Classical.allDefinable F = let_fun I := fun (x : ZFSet) => Classical.allDefinable (F x); PSet.Definable.EqMk ⟨fun (x : PSet) => ↑(PSet.Definable.Resp (F ⟦x⟧)), ⋯⟩ ⋯

def ZFSet.mk : PSet → ZFSet

Turns a pre-set into a ZFC set.

Equations

• ZFSet.mk = Quotient.mk''

@[simp]

theorem ZFSet.mk_eq (x : PSet) : ⟦x⟧ = ZFSet.mk x

@[simp]

theorem ZFSet.mk_out (x : ZFSet) : ZFSet.mk (Quotient.out x) = x

theorem ZFSet.eq {x : PSet} {y : PSet} : ZFSet.mk x = ZFSet.mk y ↔ x.Equiv y

theorem ZFSet.sound {x : PSet} {y : PSet} (h : x.Equiv y) : ZFSet.mk x = ZFSet.mk y

theorem ZFSet.exact {x : PSet} {y : PSet} : ZFSet.mk x = ZFSet.mk y → x.Equiv y

@[simp]

theorem ZFSet.eval_mk {n : ℕ} {f : PSet.Resp (n + 1)} {x : PSet} : PSet.Resp.eval (n + 1) f (ZFSet.mk x) = PSet.Resp.eval n (f.f x)

def ZFSet.Mem : ZFSet → ZFSet → Prop

The membership relation for ZFC sets is inherited from the membership relation for pre-sets.

Equations

• ZFSet.Mem = Quotient.lift₂ PSet.Mem ZFSet.Mem.proof_1

instance ZFSet.instMembership : Membership ZFSet ZFSet

Equations

• ZFSet.instMembership = { mem := ZFSet.Mem }

@[simp]

theorem ZFSet.mk_mem_iff {x : PSet} {y : PSet} : ZFSet.mk x ∈ ZFSet.mk y ↔ x ∈ y

def ZFSet.toSet (u : ZFSet) : Set ZFSet

Convert a ZFC set into a Set of ZFC sets

Equations

• u.toSet = {x : ZFSet | x ∈ u}

@[simp]

theorem ZFSet.mem_toSet (a : ZFSet) (u : ZFSet) : a ∈ u.toSet ↔ a ∈ u

instance ZFSet.small_toSet (x : ZFSet) : Small.{u, u + 1} ↑x.toSet

Equations

• ⋯ = ⋯

def ZFSet.Nonempty (u : ZFSet) : Prop

A nonempty set is one that contains some element.

Equations

• u.Nonempty = u.toSet.Nonempty

theorem ZFSet.nonempty_def (u : ZFSet) : u.Nonempty ↔ ∃ (x : ZFSet), x ∈ u

theorem ZFSet.nonempty_of_mem {x : ZFSet} {u : ZFSet} (h : x ∈ u) : u.Nonempty

@[simp]

theorem ZFSet.nonempty_toSet_iff {u : ZFSet} : u.toSet.Nonempty ↔ u.Nonempty

def ZFSet.Subset (x : ZFSet) (y : ZFSet) : Prop

x ⊆ y as ZFC sets means that all members of x are members of y.

Equations

• x.Subset y = ∀ ⦃z : ZFSet⦄, z ∈ x → z ∈ y

instance ZFSet.hasSubset : HasSubset ZFSet

Equations

• ZFSet.hasSubset = { Subset := ZFSet.Subset }

theorem ZFSet.subset_def {x : ZFSet} {y : ZFSet} : x ⊆ y ↔ ∀ ⦃z : ZFSet⦄, z ∈ x → z ∈ y

instance ZFSet.instIsReflSubset : IsRefl ZFSet fun (x x_1 : ZFSet) => x ⊆ x_1

Equations

• ZFSet.instIsReflSubset = ⋯

instance ZFSet.instIsTransSubset : IsTrans ZFSet fun (x x_1 : ZFSet) => x ⊆ x_1

Equations

• ZFSet.instIsTransSubset = ⋯

@[simp]

theorem ZFSet.subset_iff {x : PSet} {y : PSet} : ZFSet.mk x ⊆ ZFSet.mk y ↔ x ⊆ y

@[simp]

theorem ZFSet.toSet_subset_iff {x : ZFSet} {y : ZFSet} : x.toSet ⊆ y.toSet ↔ x ⊆ y

theorem ZFSet.ext {x : ZFSet} {y : ZFSet} : (∀ (z : ZFSet), z ∈ x ↔ z ∈ y) → x = y

theorem ZFSet.ext_iff {x : ZFSet} {y : ZFSet} : x = y ↔ ∀ (z : ZFSet), z ∈ x ↔ z ∈ y

theorem ZFSet.toSet_injective : Function.Injective ZFSet.toSet

@[simp]

theorem ZFSet.toSet_inj {x : ZFSet} {y : ZFSet} : x.toSet = y.toSet ↔ x = y

instance ZFSet.instIsAntisymmSubset : IsAntisymm ZFSet fun (x x_1 : ZFSet) => x ⊆ x_1

Equations

• ZFSet.instIsAntisymmSubset = ⋯

def ZFSet.empty : ZFSet

The empty ZFC set

Equations

• ZFSet.empty = ZFSet.mk ∅

instance ZFSet.instEmptyCollection : EmptyCollection ZFSet

Equations

• ZFSet.instEmptyCollection = { emptyCollection := ZFSet.empty }

instance ZFSet.instInhabited : Inhabited ZFSet

Equations

• ZFSet.instInhabited = { default := ∅ }

@[simp]

theorem ZFSet.not_mem_empty (x : ZFSet) : x ∉ ∅

@[simp]

theorem ZFSet.toSet_empty : ∅.toSet = ∅

@[simp]

theorem ZFSet.empty_subset (x : ZFSet) : ∅ ⊆ x

@[simp]

theorem ZFSet.not_nonempty_empty : ¬∅.Nonempty

@[simp]

theorem ZFSet.nonempty_mk_iff {x : PSet} : (ZFSet.mk x).Nonempty ↔ x.Nonempty

theorem ZFSet.eq_empty (x : ZFSet) : x = ∅ ↔ ∀ (y : ZFSet), y ∉ x

theorem ZFSet.eq_empty_or_nonempty (u : ZFSet) : u = ∅ ∨ u.Nonempty

def ZFSet.Insert : ZFSet → ZFSet → ZFSet

Insert x y is the set {x} ∪ y

Equations

• ZFSet.Insert = PSet.Resp.eval 2 ⟨PSet.insert, ZFSet.Insert.proof_1⟩

instance ZFSet.instInsert : Insert ZFSet ZFSet

Equations

• ZFSet.instInsert = { insert := ZFSet.Insert }

instance ZFSet.instSingleton : Singleton ZFSet ZFSet

Equations

• ZFSet.instSingleton = { singleton := fun (x : ZFSet) => insert x ∅ }

instance ZFSet.instLawfulSingleton : LawfulSingleton ZFSet ZFSet

Equations

• ZFSet.instLawfulSingleton = ⋯

@[simp]

theorem ZFSet.mem_insert_iff {x : ZFSet} {y : ZFSet} {z : ZFSet} : x ∈ insert y z ↔ x = y ∨ x ∈ z

theorem ZFSet.mem_insert (x : ZFSet) (y : ZFSet) : x ∈ insert x y

theorem ZFSet.mem_insert_of_mem {y : ZFSet} {z : ZFSet} (x : ZFSet) (h : z ∈ y) : z ∈ insert x y

@[simp]

theorem ZFSet.toSet_insert (x : ZFSet) (y : ZFSet) : (insert x y).toSet = insert x y.toSet

@[simp]

theorem ZFSet.mem_singleton {x : ZFSet} {y : ZFSet} : x ∈ {y} ↔ x = y

@[simp]

theorem ZFSet.toSet_singleton (x : ZFSet) : {x}.toSet = {x}

theorem ZFSet.insert_nonempty (u : ZFSet) (v : ZFSet) : (insert u v).Nonempty

theorem ZFSet.singleton_nonempty (u : ZFSet) : {u}.Nonempty

theorem ZFSet.mem_pair {x : ZFSet} {y : ZFSet} {z : ZFSet} : x ∈ {y, z} ↔ x = y ∨ x = z

def ZFSet.omega : ZFSet

omega is the first infinite von Neumann ordinal

Equations

• ZFSet.omega = ZFSet.mk PSet.omega

@[simp]

theorem ZFSet.omega_zero : ∅ ∈ ZFSet.omega

@[simp]

theorem ZFSet.omega_succ {n : ZFSet} : n ∈ ZFSet.omega → insert n n ∈ ZFSet.omega

def ZFSet.sep (p : ZFSet → Prop) : ZFSet → ZFSet

{x ∈ a | p x} is the set of elements in a satisfying p

Equations

• ZFSet.sep p = PSet.Resp.eval 1 ⟨PSet.sep fun (y : PSet) => p (ZFSet.mk y), ⋯⟩

instance ZFSet.instSep : Sep ZFSet ZFSet

Equations

• ZFSet.instSep = { sep := ZFSet.sep }

@[simp]

theorem ZFSet.mem_sep {p : ZFSet → Prop} {x : ZFSet} {y : ZFSet} : y ∈ ZFSet.sep p x ↔ y ∈ x ∧ p y

@[simp]

theorem ZFSet.toSet_sep (a : ZFSet) (p : ZFSet → Prop) : (ZFSet.sep p a).toSet = {x : ZFSet | x ∈ a.toSet ∧ p x}

def ZFSet.powerset : ZFSet → ZFSet

The powerset operation, the collection of subsets of a ZFC set

Equations

• ZFSet.powerset = PSet.Resp.eval 1 ⟨PSet.powerset, ZFSet.powerset.proof_1⟩

@[simp]

theorem ZFSet.mem_powerset {x : ZFSet} {y : ZFSet} : y ∈ x.powerset ↔ y ⊆ x

theorem ZFSet.sUnion_lem {α : Type u} {β : Type u} (A : α → PSet) (B : β → PSet) (αβ : ∀ (a : α), ∃ (b : β), (A a).Equiv (B b)) (a : (⋃₀ PSet.mk α A).Type) : ∃ (b : (⋃₀ PSet.mk β B).Type), ((⋃₀ PSet.mk α A).Func a).Equiv ((⋃₀ PSet.mk β B).Func b)

def ZFSet.sUnion : ZFSet → ZFSet

The union operator, the collection of elements of elements of a ZFC set

Equations

• ZFSet.sUnion = PSet.Resp.eval 1 ⟨PSet.sUnion, ZFSet.sUnion.proof_1⟩

def ZFSet.«term⋃₀_» : Lean.ParserDescr

The union operator, the collection of elements of elements of a ZFC set

Equations

• ZFSet.«term⋃₀_» = Lean.ParserDescr.node `ZFSet.term⋃₀_ 110 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol "⋃₀ ") (Lean.ParserDescr.cat `term 110))

noncomputable def ZFSet.sInter (x : ZFSet) : ZFSet

The intersection operator, the collection of elements in all of the elements of a ZFC set. We special-case ⋂₀ ∅ = ∅.

Equations

• ⋂₀ x = if h : x.Nonempty then ZFSet.sep (fun (y : ZFSet) => ∀ z ∈ x, y ∈ z) (Set.Nonempty.some h) else ∅

def ZFSet.«term⋂₀_» : Lean.ParserDescr

The intersection operator, the collection of elements in all of the elements of a ZFC set. We special-case ⋂₀ ∅ = ∅.

Equations

• ZFSet.«term⋂₀_» = Lean.ParserDescr.node `ZFSet.term⋂₀_ 110 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol "⋂₀ ") (Lean.ParserDescr.cat `term 110))

@[simp]

theorem ZFSet.mem_sUnion {x : ZFSet} {y : ZFSet} : y ∈ ⋃₀ x ↔ ∃ z ∈ x, y ∈ z

theorem ZFSet.mem_sInter {x : ZFSet} {y : ZFSet} (h : x.Nonempty) : y ∈ ⋂₀ x ↔ ∀ z ∈ x, y ∈ z

@[simp]

theorem ZFSet.sUnion_empty : ⋃₀ ∅ = ∅

@[simp]

theorem ZFSet.sInter_empty : ⋂₀ ∅ = ∅

theorem ZFSet.mem_of_mem_sInter {x : ZFSet} {y : ZFSet} {z : ZFSet} (hy : y ∈ ⋂₀ x) (hz : z ∈ x) : y ∈ z

theorem ZFSet.mem_sUnion_of_mem {x : ZFSet} {y : ZFSet} {z : ZFSet} (hy : y ∈ z) (hz : z ∈ x) : y ∈ ⋃₀ x

theorem ZFSet.not_mem_sInter_of_not_mem {x : ZFSet} {y : ZFSet} {z : ZFSet} (hy : y ∉ z) (hz : z ∈ x) : y ∉ ⋂₀ x

@[simp]

theorem ZFSet.sUnion_singleton {x : ZFSet} : ⋃₀ {x} = x

@[simp]

theorem ZFSet.sInter_singleton {x : ZFSet} : ⋂₀ {x} = x

@[simp]

theorem ZFSet.toSet_sUnion (x : ZFSet) : (⋃₀ x).toSet = ⋃₀ (ZFSet.toSet '' x.toSet)

theorem ZFSet.toSet_sInter {x : ZFSet} (h : x.Nonempty) : (⋂₀ x).toSet = ⋂₀ (ZFSet.toSet '' x.toSet)

theorem ZFSet.singleton_injective : Function.Injective singleton

@[simp]

theorem ZFSet.singleton_inj {x : ZFSet} {y : ZFSet} : {x} = {y} ↔ x = y

def ZFSet.union (x : ZFSet) (y : ZFSet) : ZFSet

The binary union operation

Equations

• x.union y = ⋃₀ {x, y}

def ZFSet.inter (x : ZFSet) (y : ZFSet) : ZFSet

The binary intersection operation

Equations

• x.inter y = ZFSet.sep (fun (z : ZFSet) => z ∈ y) x

def ZFSet.diff (x : ZFSet) (y : ZFSet) : ZFSet

The set difference operation

Equations

• x.diff y = ZFSet.sep (fun (z : ZFSet) => z ∉ y) x

instance ZFSet.instUnion : Union ZFSet

Equations

• ZFSet.instUnion = { union := ZFSet.union }

instance ZFSet.instInter : Inter ZFSet

Equations

• ZFSet.instInter = { inter := ZFSet.inter }

instance ZFSet.instSDiff : SDiff ZFSet

Equations

• ZFSet.instSDiff = { sdiff := ZFSet.diff }

@[simp]

theorem ZFSet.toSet_union (x : ZFSet) (y : ZFSet) : (x ∪ y).toSet = x.toSet ∪ y.toSet

@[simp]

theorem ZFSet.toSet_inter (x : ZFSet) (y : ZFSet) : (x ∩ y).toSet = x.toSet ∩ y.toSet

@[simp]

theorem ZFSet.toSet_sdiff (x : ZFSet) (y : ZFSet) : (x \ y).toSet = x.toSet \ y.toSet

@[simp]

theorem ZFSet.mem_union {x : ZFSet} {y : ZFSet} {z : ZFSet} : z ∈ x ∪ y ↔ z ∈ x ∨ z ∈ y

@[simp]

theorem ZFSet.mem_inter {x : ZFSet} {y : ZFSet} {z : ZFSet} : z ∈ x ∩ y ↔ z ∈ x ∧ z ∈ y

@[simp]

theorem ZFSet.mem_diff {x : ZFSet} {y : ZFSet} {z : ZFSet} : z ∈ x \ y ↔ z ∈ x ∧ z ∉ y

@[simp]

theorem ZFSet.sUnion_pair {x : ZFSet} {y : ZFSet} : ⋃₀ {x, y} = x ∪ y

theorem ZFSet.mem_wf : WellFounded fun (x x_1 : ZFSet) => x ∈ x_1

theorem ZFSet.inductionOn {p : ZFSet → Prop} (x : ZFSet) (h : ∀ (x : ZFSet), (∀ y ∈ x, p y) → p x) : p x

Induction on the ∈ relation.

instance ZFSet.instWellFoundedRelation : WellFoundedRelation ZFSet

Equations

• ZFSet.instWellFoundedRelation = { rel := fun (x x_1 : ZFSet) => x ∈ x_1, wf := ZFSet.mem_wf }

instance ZFSet.instIsAsymmMem : IsAsymm ZFSet fun (x x_1 : ZFSet) => x ∈ x_1

Equations

• ZFSet.instIsAsymmMem = ⋯

instance ZFSet.instIsIrreflMem : IsIrrefl ZFSet fun (x x_1 : ZFSet) => x ∈ x_1

Equations

• ZFSet.instIsIrreflMem = ⋯

theorem ZFSet.mem_asymm {x : ZFSet} {y : ZFSet} : x ∈ y → y ∉ x

theorem ZFSet.mem_irrefl (x : ZFSet) : x ∉ x

theorem ZFSet.regularity (x : ZFSet) (h : x ≠ ∅) : ∃ y ∈ x, x ∩ y = ∅

def ZFSet.image (f : ZFSet → ZFSet) [PSet.Definable 1 f] : ZFSet → ZFSet

The image of a (definable) ZFC set function

Equations

• ZFSet.image f = match (motive := PSet.Resp 1 → ZFSet → ZFSet) PSet.Definable.Resp f with | ⟨r, hr⟩ => PSet.Resp.eval 1 ⟨PSet.image r, ⋯⟩

theorem ZFSet.image.mk (f : ZFSet → ZFSet) [H : PSet.Definable 1 f] (x : ZFSet) {y : ZFSet} : y ∈ x → f y ∈ ZFSet.image f x

@[simp]

theorem ZFSet.mem_image {f : ZFSet → ZFSet} [H : PSet.Definable 1 f] {x : ZFSet} {y : ZFSet} : y ∈ ZFSet.image f x ↔ ∃ z ∈ x, f z = y

@[simp]

theorem ZFSet.toSet_image (f : ZFSet → ZFSet) [H : PSet.Definable 1 f] (x : ZFSet) : (ZFSet.image f x).toSet = f '' x.toSet

noncomputable def ZFSet.range {α : Type u} (f : α → ZFSet) : ZFSet

The range of an indexed family of sets. The universes allow for a more general index type without manual use of ULift.

Equations

• ZFSet.range f = ⟦PSet.mk (ULift.{v, u} α) (Quotient.out ∘ f ∘ ULift.down)⟧

@[simp]

theorem ZFSet.mem_range {α : Type u} {f : α → ZFSet} {x : ZFSet} : x ∈ ZFSet.range f ↔ x ∈ Set.range f

@[simp]

theorem ZFSet.toSet_range {α : Type u} (f : α → ZFSet) : (ZFSet.range f).toSet = Set.range f

def ZFSet.pair (x : ZFSet) (y : ZFSet) : ZFSet

Kuratowski ordered pair

Equations

• x.pair y = {{x}, {x, y}}

@[simp]

theorem ZFSet.toSet_pair (x : ZFSet) (y : ZFSet) : (x.pair y).toSet = {{x}, {x, y}}

def ZFSet.pairSep (p : ZFSet → ZFSet → Prop) (x : ZFSet) (y : ZFSet) : ZFSet

A subset of pairs {(a, b) ∈ x × y | p a b}

Equations

• ZFSet.pairSep p x y = ZFSet.sep (fun (z : ZFSet) => ∃ a ∈ x, ∃ b ∈ y, z = a.pair b ∧ p a b) (x ∪ y).powerset.powerset

@[simp]

theorem ZFSet.mem_pairSep {p : ZFSet → ZFSet → Prop} {x : ZFSet} {y : ZFSet} {z : ZFSet} : z ∈ ZFSet.pairSep p x y ↔ ∃ a ∈ x, ∃ b ∈ y, z = a.pair b ∧ p a b

theorem ZFSet.pair_injective : Function.Injective2 ZFSet.pair

@[simp]

theorem ZFSet.pair_inj {x : ZFSet} {y : ZFSet} {x' : ZFSet} {y' : ZFSet} : x.pair y = x'.pair y' ↔ x = x' ∧ y = y'

def ZFSet.prod : ZFSet → ZFSet → ZFSet

The cartesian product, {(a, b) | a ∈ x, b ∈ y}

Equations

• ZFSet.prod = ZFSet.pairSep fun (x x : ZFSet) => True

@[simp]

theorem ZFSet.mem_prod {x : ZFSet} {y : ZFSet} {z : ZFSet} : z ∈ x.prod y ↔ ∃ a ∈ x, ∃ b ∈ y, z = a.pair b

theorem ZFSet.pair_mem_prod {x : ZFSet} {y : ZFSet} {a : ZFSet} {b : ZFSet} : a.pair b ∈ x.prod y ↔ a ∈ x ∧ b ∈ y

def ZFSet.IsFunc (x : ZFSet) (y : ZFSet) (f : ZFSet) : Prop

isFunc x y f is the assertion that f is a subset of x × y which relates to each element of x a unique element of y, so that we can consider f as a ZFC function x → y.

Equations

• x.IsFunc y f = (f ⊆ x.prod y ∧ ∀ z ∈ x, ∃! w : ZFSet, z.pair w ∈ f)

def ZFSet.funs (x : ZFSet) (y : ZFSet) : ZFSet

funs x y is y ^ x, the set of all set functions x → y

Equations

• x.funs y = ZFSet.sep (x.IsFunc y) (x.prod y).powerset

@[simp]

theorem ZFSet.mem_funs {x : ZFSet} {y : ZFSet} {f : ZFSet} : f ∈ x.funs y ↔ x.IsFunc y f

noncomputable instance ZFSet.mapDefinableAux (f : ZFSet → ZFSet) [PSet.Definable 1 f] : PSet.Definable 1 fun (y : ZFSet) => y.pair (f y)

Equations

• ZFSet.mapDefinableAux f = Classical.allDefinable fun (y : ZFSet) => y.pair (f y)

noncomputable def ZFSet.map (f : ZFSet → ZFSet) [PSet.Definable 1 f] : ZFSet → ZFSet

Graph of a function: map f x is the ZFC function which maps a ∈ x to f a

Equations

• ZFSet.map f = ZFSet.image fun (y : ZFSet) => y.pair (f y)

@[simp]

theorem ZFSet.mem_map {f : ZFSet → ZFSet} [PSet.Definable 1 f] {x : ZFSet} {y : ZFSet} : y ∈ ZFSet.map f x ↔ ∃ z ∈ x, z.pair (f z) = y

theorem ZFSet.map_unique {f : ZFSet → ZFSet} [H : PSet.Definable 1 f] {x : ZFSet} {z : ZFSet} (zx : z ∈ x) : ∃! w : ZFSet, z.pair w ∈ ZFSet.map f x

@[simp]

theorem ZFSet.map_isFunc {f : ZFSet → ZFSet} [PSet.Definable 1 f] {x : ZFSet} {y : ZFSet} : x.IsFunc y (ZFSet.map f x) ↔ ∀ z ∈ x, f z ∈ y

@[irreducible]

def ZFSet.Hereditarily (p : ZFSet → Prop) (x : ZFSet) : Prop

Given a predicate p on ZFC sets. Hereditarily p x means that x has property p and the members of x are all Hereditarily p.

Equations

• ZFSet.Hereditarily p x = (p x ∧ ∀ y ∈ x, ZFSet.Hereditarily p y)

theorem ZFSet.hereditarily_iff {p : ZFSet → Prop} {x : ZFSet} : ZFSet.Hereditarily p x ↔ p x ∧ ∀ y ∈ x, ZFSet.Hereditarily p y

theorem ZFSet.Hereditarily.def {p : ZFSet → Prop} {x : ZFSet} : ZFSet.Hereditarily p x → p x ∧ ∀ y ∈ x, ZFSet.Hereditarily p y

Alias of the forward direction of ZFSet.hereditarily_iff.

theorem ZFSet.Hereditarily.self {p : ZFSet → Prop} {x : ZFSet} (h : ZFSet.Hereditarily p x) : p x

theorem ZFSet.Hereditarily.mem {p : ZFSet → Prop} {x : ZFSet} {y : ZFSet} (h : ZFSet.Hereditarily p x) (hy : y ∈ x) : ZFSet.Hereditarily p y

theorem ZFSet.Hereditarily.empty {p : ZFSet → Prop} {x : ZFSet} : ZFSet.Hereditarily p x → p ∅

def Class : Type (u_1 + 1)

The collection of all classes. We define Class as Set ZFSet, as this allows us to get many instances automatically. However, in practice, we treat it as (the definitionally equal) ZFSet → Prop. This means, the preferred way to state that x : ZFSet belongs to A : Class is to write A x.

Equations

• Class = Set ZFSet

instance instInsertZFSetClass : Insert ZFSet Class

Equations

• instInsertZFSetClass = { insert := Set.insert }

def Class.sep (p : ZFSet → Prop) (A : Class) : Class

{x ∈ A | p x} is the class of elements in A satisfying p

Equations

• Class.sep p A = {y : ZFSet | A y ∧ p y}

theorem Class.ext {x : Class} {y : Class} : (∀ (z : ZFSet), x z ↔ y z) → x = y

theorem Class.ext_iff {x : Class} {y : Class} : x = y ↔ ∀ (z : ZFSet), x z ↔ y z

def Class.ofSet (x : ZFSet) : Class

Coerce a ZFC set into a class

Equations

• ↑x = {y : ZFSet | y ∈ x}

instance Class.instCoeZFSet : Coe ZFSet Class

Equations

• Class.instCoeZFSet = { coe := Class.ofSet }

def Class.univ : Class

The universal class

Equations

• Class.univ = Set.univ

def Class.ToSet (B : Class) (A : Class) : Prop

Assert that A is a ZFC set satisfying B

Equations

• B.ToSet A = ∃ (x : ZFSet), ↑x = A ∧ B x

def Class.Mem (A : Class) (B : Class) : Prop

A ∈ B if A is a ZFC set which satisfies B

Equations

• A.Mem B = B.ToSet A

instance Class.instMembership : Membership Class Class

Equations

• Class.instMembership = { mem := Class.Mem }

theorem Class.mem_def (A : Class) (B : Class) : A ∈ B ↔ ∃ (x : ZFSet), ↑x = A ∧ B x

@[simp]

theorem Class.not_mem_empty (x : Class) : x ∉ ∅

@[simp]

theorem Class.not_empty_hom (x : ZFSet) : ¬∅ x

@[simp]

theorem Class.mem_univ {A : Class} : A ∈ Class.univ ↔ ∃ (x : ZFSet), ↑x = A

@[simp]

theorem Class.mem_univ_hom (x : ZFSet) : Class.univ x

theorem Class.eq_univ_iff_forall {A : Class} : A = Class.univ ↔ ∀ (x : ZFSet), A x

theorem Class.eq_univ_of_forall {A : Class} : (∀ (x : ZFSet), A x) → A = Class.univ

theorem Class.mem_wf : WellFounded fun (x x_1 : Class) => x ∈ x_1

instance Class.instWellFoundedRelation : WellFoundedRelation Class

Equations

• Class.instWellFoundedRelation = { rel := fun (x x_1 : Class) => x ∈ x_1, wf := Class.mem_wf }

instance Class.instIsAsymmMem : IsAsymm Class fun (x x_1 : Class) => x ∈ x_1

Equations

• Class.instIsAsymmMem = ⋯

instance Class.instIsIrreflMem : IsIrrefl Class fun (x x_1 : Class) => x ∈ x_1

Equations

• Class.instIsIrreflMem = ⋯

theorem Class.mem_asymm {x : Class} {y : Class} : x ∈ y → y ∉ x

theorem Class.mem_irrefl (x : Class) : x ∉ x

theorem Class.univ_not_mem_univ : Class.univ ∉ Class.univ

There is no universal set. This is stated as univ ∉ univ, meaning that univ (the class of all sets) is proper (does not belong to the class of all sets).

def Class.congToClass (x : Set Class) : Class

Convert a conglomerate (a collection of classes) into a class

Equations

• Class.congToClass x = {y : ZFSet | ↑y ∈ x}

@[simp]

theorem Class.congToClass_empty : Class.congToClass ∅ = ∅

def Class.classToCong (x : Class) : Set Class

Convert a class into a conglomerate (a collection of classes)

Equations

• x.classToCong = {y : Class | y ∈ x}

@[simp]

theorem Class.classToCong_empty : ∅.classToCong = ∅

def Class.powerset (x : Class) : Class

The power class of a class is the class of all subclasses that are ZFC sets

Equations

• x.powerset = Class.congToClass (𝒫 x)

def Class.sUnion (x : Class) : Class

The union of a class is the class of all members of ZFC sets in the class

Equations

• ⋃₀ x = ⋃₀ x.classToCong

def Class.«term⋃₀_» : Lean.ParserDescr

The union of a class is the class of all members of ZFC sets in the class

Equations

• Class.«term⋃₀_» = Lean.ParserDescr.node `Class.term⋃₀_ 110 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol "⋃₀ ") (Lean.ParserDescr.cat `term 110))

def Class.sInter (x : Class) : Class

The intersection of a class is the class of all members of ZFC sets in the class

Equations

• ⋂₀ x = ⋂₀ x.classToCong

def Class.«term⋂₀_» : Lean.ParserDescr

The intersection of a class is the class of all members of ZFC sets in the class

Equations

• Class.«term⋂₀_» = Lean.ParserDescr.node `Class.term⋂₀_ 110 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol "⋂₀ ") (Lean.ParserDescr.cat `term 110))

theorem Class.ofSet.inj {x : ZFSet} {y : ZFSet} (h : ↑x = ↑y) : x = y

@[simp]

theorem Class.toSet_of_ZFSet (A : Class) (x : ZFSet) : A.ToSet ↑x ↔ A x

@[simp]

theorem Class.coe_mem {x : ZFSet} {A : Class} : ↑x ∈ A ↔ A x

@[simp]

theorem Class.coe_apply {x : ZFSet} {y : ZFSet} : ↑y x ↔ x ∈ y

@[simp]

theorem Class.coe_subset (x : ZFSet) (y : ZFSet) : ↑x ⊆ ↑y ↔ x ⊆ y

@[simp]

theorem Class.coe_sep (p : Class) (x : ZFSet) : ↑(ZFSet.sep p x) = {y : ZFSet | y ∈ x ∧ p y}

@[simp]

theorem Class.coe_empty : ↑∅ = ∅

@[simp]

theorem Class.coe_insert (x : ZFSet) (y : ZFSet) : ↑(insert x y) = insert x ↑y

@[simp]

theorem Class.coe_union (x : ZFSet) (y : ZFSet) : ↑(x ∪ y) = ↑x ∪ ↑y

@[simp]

theorem Class.coe_inter (x : ZFSet) (y : ZFSet) : ↑(x ∩ y) = ↑x ∩ ↑y

@[simp]

theorem Class.coe_diff (x : ZFSet) (y : ZFSet) : ↑(x \ y) = ↑x \ ↑y

@[simp]

theorem Class.coe_powerset (x : ZFSet) : ↑x.powerset = (↑x).powerset

@[simp]

theorem Class.powerset_apply {A : Class} {x : ZFSet} : A.powerset x ↔ ↑x ⊆ A

@[simp]

theorem Class.sUnion_apply {x : Class} {y : ZFSet} : (⋃₀ x) y ↔ ∃ (z : ZFSet), x z ∧ y ∈ z

@[simp]

theorem Class.coe_sUnion (x : ZFSet) : ↑(⋃₀ x) = ⋃₀ ↑x

@[simp]

theorem Class.mem_sUnion {x : Class} {y : Class} : y ∈ ⋃₀ x ↔ ∃ z ∈ x, y ∈ z

theorem Class.sInter_apply {x : Class} {y : ZFSet} : (⋂₀ x) y ↔ ∀ (z : ZFSet), x z → y ∈ z

@[simp]

theorem Class.coe_sInter {x : ZFSet} (h : x.Nonempty) : ↑(⋂₀ x) = ⋂₀ ↑x

theorem Class.mem_of_mem_sInter {x : Class} {y : Class} {z : Class} (hy : y ∈ ⋂₀ x) (hz : z ∈ x) : y ∈ z

theorem Class.mem_sInter {x : Class} {y : Class} (h : Set.Nonempty x) : y ∈ ⋂₀ x ↔ ∀ z ∈ x, y ∈ z

@[simp]

theorem Class.sUnion_empty : ⋃₀ ∅ = ∅

@[simp]

theorem Class.sInter_empty : ⋂₀ ∅ = Class.univ

theorem Class.eq_univ_of_powerset_subset {A : Class} (hA : A.powerset ⊆ A) : A = Class.univ

An induction principle for sets. If every subset of a class is a member, then the class is universal.

def Class.iota (A : Class) : Class

The definite description operator, which is {x} if {y | A y} = {x} and ∅ otherwise.

Equations

• A.iota = ⋃₀ {x : ZFSet | ∀ (y : ZFSet), A y ↔ y = x}

theorem Class.iota_val (A : Class) (x : ZFSet) (H : ∀ (y : ZFSet), A y ↔ y = x) : A.iota = ↑x

theorem Class.iota_ex (A : Class) : A.iota ∈ Class.univ

Unlike the other set constructors, the iota definite descriptor is a set for any set input, but not constructively so, so there is no associated Class → Set function.

def Class.fval (F : Class) (A : Class) : Class

Function value

Equations

• F ′ A = Class.iota fun (y : ZFSet) => Class.ToSet (fun (x : ZFSet) => F (x.pair y)) A

def Class.«term_′_» : Lean.TrailingParserDescr

Function value

Equations

• Class.«term_′_» = Lean.ParserDescr.trailingNode `Class.term_′_ 100 100 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol " ′ ") (Lean.ParserDescr.cat `term 101))

theorem Class.fval_ex (F : Class) (A : Class) : F ′ A ∈ Class.univ

@[simp]

theorem ZFSet.map_fval {f : ZFSet → ZFSet} [H : PSet.Definable 1 f] {x : ZFSet} {y : ZFSet} (h : y ∈ x) : ↑(ZFSet.map f x) ′ ↑y = ↑(f y)

noncomputable def ZFSet.choice (x : ZFSet) : ZFSet

A choice function on the class of nonempty ZFC sets.

Equations

• x.choice = ZFSet.map (fun (y : ZFSet) => Classical.epsilon fun (z : ZFSet) => z ∈ y) x

theorem ZFSet.choice_mem_aux (x : ZFSet) (h : ∅ ∉ x) (y : ZFSet) (yx : y ∈ x) : (Classical.epsilon fun (z : ZFSet) => z ∈ y) ∈ y

theorem ZFSet.choice_isFunc (x : ZFSet) (h : ∅ ∉ x) : x.IsFunc (⋃₀ x) x.choice

theorem ZFSet.choice_mem (x : ZFSet) (h : ∅ ∉ x) (y : ZFSet) (yx : y ∈ x) : ↑x.choice ′ ↑y ∈ ↑y

@[simp]

theorem ZFSet.toSet_equiv_apply_coe (x : ZFSet) : ↑(ZFSet.toSet_equiv x) = x.toSet

noncomputable def ZFSet.toSet_equiv : ZFSet ≃ { s : Set ZFSet // Small.{u, u + 1} ↑s }

ZFSet.toSet as an equivalence.

Equations

• One or more equations did not get rendered due to their size.