Ordinals

Ordinals are defined as equivalences of well-ordered sets under order isomorphism. They are endowed with a total order, where an ordinal is smaller than another one if it embeds into it as an initial segment (or, equivalently, in any way). This total order is well founded.

Main definitions

• Ordinal: the type of ordinals (in a given universe)

• Ordinal.type r: given a well-founded order r, this is the corresponding ordinal

• Ordinal.typein r a: given a well-founded order r on a type α, and a : α, the ordinal corresponding to all elements smaller than a.

• enum r o h: given a well-order r on a type α, and an ordinal o strictly smaller than the ordinal corresponding to r (this is the assumption h), returns the o-th element of α. In other words, the elements of α can be enumerated using ordinals up to type r.

• Ordinal.card o: the cardinality of an ordinal o.

• Ordinal.lift lifts an ordinal in universe u to an ordinal in universe max u v. For a version registering additionally that this is an initial segment embedding, see Ordinal.lift.initialSeg. For a version registering that it is a principal segment embedding if u < v, see Ordinal.lift.principalSeg.

• Ordinal.omega or ω is the order type of ℕ. This definition is universe polymorphic: Ordinal.omega.{u} : Ordinal.{u} (contrast with ℕ : Type, which lives in a specific universe). In some cases the universe level has to be given explicitly.

• o₁ + o₂ is the order on the disjoint union of o₁ and o₂ obtained by declaring that every element of o₁ is smaller than every element of o₂. The main properties of addition (and the other operations on ordinals) are stated and proved in Mathlib/SetTheory/Ordinal/Arithmetic.lean. Here, we only introduce it and prove its basic properties to deduce the fact that the order on ordinals is total (and well founded).

• succ o is the successor of the ordinal o.

• Cardinal.ord c: when c is a cardinal, ord c is the smallest ordinal with this cardinality. It is the canonical way to represent a cardinal with an ordinal.

A conditionally complete linear order with bot structure is registered on ordinals, where ⊥ is 0, the ordinal corresponding to the empty type, and Inf is the minimum for nonempty sets and 0 for the empty set by convention.

Notations

• ω is a notation for the first infinite ordinal in the locale Ordinal.

Well order on an arbitrary type

theorem nonempty_embedding_to_cardinal {σ : Type u} : Nonempty (σ ↪ Cardinal.{u})

def embeddingToCardinal {σ : Type u} : σ ↪ Cardinal.{u}

An embedding of any type to the set of cardinals.

Equations

• embeddingToCardinal = Classical.choice ⋯

def WellOrderingRel {σ : Type u} : σ → σ → Prop

Any type can be endowed with a well order, obtained by pulling back the well order over cardinals by some embedding.

Equations

• WellOrderingRel = ⇑embeddingToCardinal ⁻¹'o fun (x x_1 : Cardinal.{u}) => x < x_1

instance WellOrderingRel.isWellOrder {σ : Type u} : IsWellOrder σ WellOrderingRel

Equations

• ⋯ = ⋯

instance IsWellOrder.subtype_nonempty {σ : Type u} : Nonempty { r : σ → σ → Prop // IsWellOrder σ r }

Equations

• ⋯ = ⋯

Definition of ordinals

structure WellOrder : Type (u + 1)

Bundled structure registering a well order on a type. Ordinals will be defined as a quotient of this type.

• α : Type u

  The underlying type of the order.

• r : self.α → self.α → Prop

  The underlying relation of the order.

• wo : IsWellOrder self.α self.r

  The proposition that r is a well-ordering for α.

instance WellOrder.inhabited : Inhabited WellOrder

Equations

• WellOrder.inhabited = { default := { α := PEmpty.{u_3 + 1} , r := EmptyRelation, wo := WellOrder.inhabited.proof_1 } }

@[simp]

theorem WellOrder.eta (o : WellOrder) : { α := o.α, r := o.r, wo := ⋯ } = o

instance Ordinal.isEquivalent : Setoid WellOrder

Equivalence relation on well orders on arbitrary types in universe u, given by order isomorphism.

Equations

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

def Ordinal : Type (u + 1)

Ordinal.{u} is the type of well orders in Type u, up to order isomorphism.

Equations

• Ordinal.{u} = Quotient Ordinal.isEquivalent

instance hasWellFoundedOut (o : Ordinal.{u_3}) : WellFoundedRelation (Quotient.out o).α

Equations

• hasWellFoundedOut o = { rel := (Quotient.out o).r, wf := ⋯ }

instance linearOrderOut (o : Ordinal.{u_3}) : LinearOrder (Quotient.out o).α

Equations

• linearOrderOut o = IsWellOrder.linearOrder (Quotient.out o).r

instance isWellOrder_out_lt (o : Ordinal.{u_3}) : IsWellOrder (Quotient.out o).α fun (x x_1 : (Quotient.out o).α) => x < x_1

Equations

• ⋯ = ⋯

Basic properties of the order type

def Ordinal.type {α : Type u} (r : α → α → Prop) [wo : IsWellOrder α r] : Ordinal.{u}

The order type of a well order is an ordinal.

Equations

• Ordinal.type r = ⟦{ α := α, r := r, wo := wo }⟧

instance Ordinal.zero : Zero Ordinal.{u_3}

Equations

• Ordinal.zero = { zero := Ordinal.type EmptyRelation }

instance Ordinal.inhabited : Inhabited Ordinal.{u_3}

Equations

• Ordinal.inhabited = { default := 0 }

instance Ordinal.one : One Ordinal.{u_3}

Equations

• Ordinal.one = { one := Ordinal.type EmptyRelation }

def Ordinal.typein {α : Type u} (r : α → α → Prop) [IsWellOrder α r] (a : α) : Ordinal.{u}

The order type of an element inside a well order. For the embedding as a principal segment, see typein.principalSeg.

Equations

• Ordinal.typein r a = Ordinal.type (Subrel r {b : α | r b a})

@[simp]

theorem Ordinal.type_def' (w : WellOrder) : ⟦w⟧ = Ordinal.type w.r

@[simp]

theorem Ordinal.type_def {α : Type u} (r : α → α → Prop) [wo : IsWellOrder α r] : ⟦{ α := α, r := r, wo := wo }⟧ = Ordinal.type r

@[simp]

theorem Ordinal.type_out (o : Ordinal.{u_3}) : Ordinal.type (Quotient.out o).r = o

theorem Ordinal.type_eq {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] : Ordinal.type r = Ordinal.type s ↔ Nonempty (r ≃r s)

theorem RelIso.ordinal_type_eq {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (h : r ≃r s) : Ordinal.type r = Ordinal.type s

@[simp]

theorem Ordinal.type_lt (o : Ordinal.{u_3}) : (Ordinal.type fun (x x_1 : (Quotient.out o).α) => x < x_1) = o

theorem Ordinal.type_eq_zero_of_empty {α : Type u} (r : α → α → Prop) [IsWellOrder α r] [IsEmpty α] : Ordinal.type r = 0

@[simp]

theorem Ordinal.type_eq_zero_iff_isEmpty {α : Type u} {r : α → α → Prop} [IsWellOrder α r] : Ordinal.type r = 0 ↔ IsEmpty α

theorem Ordinal.type_ne_zero_iff_nonempty {α : Type u} {r : α → α → Prop} [IsWellOrder α r] : Ordinal.type r ≠ 0 ↔ Nonempty α

theorem Ordinal.type_ne_zero_of_nonempty {α : Type u} (r : α → α → Prop) [IsWellOrder α r] [h : Nonempty α] : Ordinal.type r ≠ 0

theorem Ordinal.type_pEmpty : Ordinal.type EmptyRelation = 0

theorem Ordinal.type_empty : Ordinal.type EmptyRelation = 0

theorem Ordinal.type_eq_one_of_unique {α : Type u} (r : α → α → Prop) [IsWellOrder α r] [Unique α] : Ordinal.type r = 1

@[simp]

theorem Ordinal.type_eq_one_iff_unique {α : Type u} {r : α → α → Prop} [IsWellOrder α r] : Ordinal.type r = 1 ↔ Nonempty (Unique α)

theorem Ordinal.type_pUnit : Ordinal.type EmptyRelation = 1

theorem Ordinal.type_unit : Ordinal.type EmptyRelation = 1

@[simp]

theorem Ordinal.out_empty_iff_eq_zero {o : Ordinal.{u_3}} : IsEmpty (Quotient.out o).α ↔ o = 0

theorem Ordinal.eq_zero_of_out_empty (o : Ordinal.{u_3}) [h : IsEmpty (Quotient.out o).α] : o = 0

instance Ordinal.isEmpty_out_zero : IsEmpty (Quotient.out 0).α

Equations

• Ordinal.isEmpty_out_zero = ⋯

@[simp]

theorem Ordinal.out_nonempty_iff_ne_zero {o : Ordinal.{u_3}} : Nonempty (Quotient.out o).α ↔ o ≠ 0

theorem Ordinal.ne_zero_of_out_nonempty (o : Ordinal.{u_3}) [h : Nonempty (Quotient.out o).α] : o ≠ 0

theorem Ordinal.one_ne_zero : 1 ≠ 0

instance Ordinal.nontrivial : Nontrivial Ordinal.{u}

Equations

• Ordinal.nontrivial = ⋯

theorem Ordinal.type_preimage {α : Type u} {β : Type u} (r : α → α → Prop) [IsWellOrder α r] (f : β ≃ α) : Ordinal.type (⇑f ⁻¹'o r) = Ordinal.type r

@[simp]

theorem Ordinal.type_preimage_aux {α : Type u} {β : Type u} (r : α → α → Prop) [IsWellOrder α r] (f : β ≃ α) : (Ordinal.type fun (x y : β) => r (f x) (f y)) = Ordinal.type r

theorem Ordinal.inductionOn {C : Ordinal.{u_3} → Prop} (o : Ordinal.{u_3}) (H : ∀ (α : Type u_3) (r : α → α → Prop) [inst : IsWellOrder α r], C (Ordinal.type r)) : C o

The order on ordinals

instance Ordinal.partialOrder : PartialOrder Ordinal.{u_3}

Equations

• Ordinal.partialOrder = PartialOrder.mk Ordinal.partialOrder.proof_6

theorem Ordinal.type_le_iff {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] : Ordinal.type r ≤ Ordinal.type s ↔ Nonempty (r ≼i s)

theorem Ordinal.type_le_iff' {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] : Ordinal.type r ≤ Ordinal.type s ↔ Nonempty (r ↪r s)

theorem InitialSeg.ordinal_type_le {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (h : r ≼i s) : Ordinal.type r ≤ Ordinal.type s

theorem RelEmbedding.ordinal_type_le {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (h : r ↪r s) : Ordinal.type r ≤ Ordinal.type s

@[simp]

theorem Ordinal.type_lt_iff {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] : Ordinal.type r < Ordinal.type s ↔ Nonempty (r ≺i s)

theorem PrincipalSeg.ordinal_type_lt {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (h : r ≺i s) : Ordinal.type r < Ordinal.type s

@[simp]

theorem Ordinal.zero_le (o : Ordinal.{u_3}) : 0 ≤ o

instance Ordinal.orderBot : OrderBot Ordinal.{u_3}

Equations

• Ordinal.orderBot = OrderBot.mk Ordinal.zero_le

@[simp]

theorem Ordinal.bot_eq_zero : ⊥ = 0

@[simp]

theorem Ordinal.le_zero {o : Ordinal.{u_3}} : o ≤ 0 ↔ o = 0

theorem Ordinal.pos_iff_ne_zero {o : Ordinal.{u_3}} : 0 < o ↔ o ≠ 0

theorem Ordinal.not_lt_zero (o : Ordinal.{u_3}) : ¬o < 0

theorem Ordinal.eq_zero_or_pos (a : Ordinal.{u_3}) : a = 0 ∨ 0 < a

instance Ordinal.zeroLEOneClass : ZeroLEOneClass Ordinal.{u_3}

Equations

• Ordinal.zeroLEOneClass = ⋯

instance Ordinal.NeZero.one : NeZero 1

Equations

• Ordinal.NeZero.one = ⋯

def Ordinal.initialSegOut {α : Ordinal.{u_3}} {β : Ordinal.{u_3}} (h : α ≤ β) : (fun (x x_1 : (Quotient.out α).α) => x < x_1) ≼i fun (x x_1 : (Quotient.out β).α) => x < x_1

Given two ordinals α ≤ β, then initialSegOut α β is the initial segment embedding of α to β, as map from a model type for α to a model type for β.

Equations

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

def Ordinal.principalSegOut {α : Ordinal.{u_3}} {β : Ordinal.{u_3}} (h : α < β) : (fun (x x_1 : (Quotient.out α).α) => x < x_1) ≺i fun (x x_1 : (Quotient.out β).α) => x < x_1

Given two ordinals α < β, then principalSegOut α β is the principal segment embedding of α to β, as map from a model type for α to a model type for β.

Equations

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

theorem Ordinal.typein_lt_type {α : Type u} (r : α → α → Prop) [IsWellOrder α r] (a : α) : Ordinal.typein r a < Ordinal.type r

theorem Ordinal.typein_lt_self {o : Ordinal.{u_3}} (i : (Quotient.out o).α) : Ordinal.typein (fun (x x_1 : (Quotient.out o).α) => x < x_1) i < o

@[simp]

theorem Ordinal.typein_top {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (f : r ≺i s) : Ordinal.typein s f.top = Ordinal.type r

@[simp]

theorem Ordinal.typein_apply {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (f : r ≼i s) (a : α) : Ordinal.typein s (f a) = Ordinal.typein r a

@[simp]

theorem Ordinal.typein_lt_typein {α : Type u} (r : α → α → Prop) [IsWellOrder α r] {a : α} {b : α} : Ordinal.typein r a < Ordinal.typein r b ↔ r a b

theorem Ordinal.typein_surj {α : Type u} (r : α → α → Prop) [IsWellOrder α r] {o : Ordinal.{u}} (h : o < Ordinal.type r) : ∃ (a : α), Ordinal.typein r a = o

theorem Ordinal.typein_injective {α : Type u} (r : α → α → Prop) [IsWellOrder α r] : Function.Injective (Ordinal.typein r)

@[simp]

theorem Ordinal.typein_inj {α : Type u} (r : α → α → Prop) [IsWellOrder α r] {a : α} {b : α} : Ordinal.typein r a = Ordinal.typein r b ↔ a = b

def Ordinal.typein.principalSeg {α : Type u} (r : α → α → Prop) [IsWellOrder α r] : r ≺i fun (x x_1 : Ordinal.{u}) => x < x_1

Principal segment version of the typein function, embedding a well order into ordinals as a principal segment.

Equations

• Ordinal.typein.principalSeg r = { toRelEmbedding := { toEmbedding := { toFun := Ordinal.typein r, inj' := ⋯ }, map_rel_iff' := ⋯ }, top := Ordinal.type r, down' := ⋯ }

@[simp]

theorem Ordinal.typein.principalSeg_coe {α : Type u} (r : α → α → Prop) [IsWellOrder α r] : ⇑(Ordinal.typein.principalSeg r).toRelEmbedding = Ordinal.typein r

Enumerating elements in a well-order with ordinals.

def Ordinal.enum {α : Type u} (r : α → α → Prop) [IsWellOrder α r] (o : Ordinal.{u}) (h : o < Ordinal.type r) : α

enum r o h is the o-th element of α ordered by r. That is, enum maps an initial segment of the ordinals, those less than the order type of r, to the elements of α.

Equations

• Ordinal.enum r o h = (PrincipalSeg.subrelIso (Ordinal.typein.principalSeg r)) { val := o, property := h }

@[simp]

theorem Ordinal.typein_enum {α : Type u} (r : α → α → Prop) [IsWellOrder α r] {o : Ordinal.{u}} (h : o < Ordinal.type r) : Ordinal.typein r (Ordinal.enum r o h) = o

theorem Ordinal.enum_type {α : Type u_3} {β : Type u_3} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (f : s ≺i r) {h : Ordinal.type s < Ordinal.type r} : Ordinal.enum r (Ordinal.type s) h = f.top

@[simp]

theorem Ordinal.enum_typein {α : Type u} (r : α → α → Prop) [IsWellOrder α r] (a : α) : Ordinal.enum r (Ordinal.typein r a) ⋯ = a

theorem Ordinal.enum_lt_enum {α : Type u} {r : α → α → Prop} [IsWellOrder α r] {o₁ : Ordinal.{u}} {o₂ : Ordinal.{u}} (h₁ : o₁ < Ordinal.type r) (h₂ : o₂ < Ordinal.type r) : r (Ordinal.enum r o₁ h₁) (Ordinal.enum r o₂ h₂) ↔ o₁ < o₂

theorem Ordinal.relIso_enum' {α : Type u} {β : Type u} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (f : r ≃r s) (o : Ordinal.{u}) (hr : o < Ordinal.type r) (hs : o < Ordinal.type s) : f (Ordinal.enum r o hr) = Ordinal.enum s o hs

theorem Ordinal.relIso_enum {α : Type u} {β : Type u} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (f : r ≃r s) (o : Ordinal.{u}) (hr : o < Ordinal.type r) : f (Ordinal.enum r o hr) = Ordinal.enum s o ⋯

theorem Ordinal.lt_wf : WellFounded fun (x x_1 : Ordinal.{u_3}) => x < x_1

instance Ordinal.wellFoundedRelation : WellFoundedRelation Ordinal.{u_3}

Equations

• Ordinal.wellFoundedRelation = { rel := fun (x x_1 : Ordinal.{u_3}) => x < x_1, wf := Ordinal.lt_wf }

theorem Ordinal.induction {p : Ordinal.{u} → Prop} (i : Ordinal.{u}) (h : ∀ (j : Ordinal.{u}), (∀ k < j, p k) → p j) : p i

Reformulation of well founded induction on ordinals as a lemma that works with the induction tactic, as in induction i using Ordinal.induction with | h i IH => ?_.

Cardinality of ordinals

def Ordinal.card : Ordinal.{u_3} → Cardinal.{u_3}

The cardinal of an ordinal is the cardinality of any type on which a relation with that order type is defined.

Equations

• Ordinal.card = Quotient.map WellOrder.α Ordinal.card.proof_1

@[simp]

theorem Ordinal.card_type {α : Type u} (r : α → α → Prop) [IsWellOrder α r] : Ordinal.card (Ordinal.type r) = Cardinal.mk α

@[simp]

theorem Ordinal.card_typein {α : Type u} {r : α → α → Prop} [IsWellOrder α r] (x : α) : Cardinal.mk { y : α // r y x } = Ordinal.card (Ordinal.typein r x)

theorem Ordinal.card_le_card {o₁ : Ordinal.{u_3}} {o₂ : Ordinal.{u_3}} : o₁ ≤ o₂ → Ordinal.card o₁ ≤ Ordinal.card o₂

@[simp]

theorem Ordinal.card_zero : Ordinal.card 0 = 0

@[simp]

theorem Ordinal.card_one : Ordinal.card 1 = 1

Lifting ordinals to a higher universe

def Ordinal.lift (o : Ordinal.{v}) : Ordinal.{max v u}

The universe lift operation for ordinals, which embeds Ordinal.{u} as a proper initial segment of Ordinal.{v} for v > u. For the initial segment version, see lift.initialSeg.

Equations

• Ordinal.lift.{u, v} o = Quotient.liftOn o (fun (w : WellOrder) => Ordinal.type (ULift.down ⁻¹'o w.r)) Ordinal.lift.proof_2

theorem Ordinal.type_uLift {α : Type u} (r : α → α → Prop) [IsWellOrder α r] : Ordinal.type (ULift.down ⁻¹'o r) = Ordinal.lift.{v, u} (Ordinal.type r)

@[simp]

theorem Ordinal.type_uLift_aux {α : Type u} (r : α → α → Prop) [IsWellOrder α r] : (Ordinal.type fun (x y : ULift.{v, u} α) => r x.down y.down) = Ordinal.lift.{v, u} (Ordinal.type r)

theorem RelIso.ordinal_lift_type_eq {α : Type u} {β : Type v} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] (f : r ≃r s) : Ordinal.lift.{v, u} (Ordinal.type r) = Ordinal.lift.{u, v} (Ordinal.type s)

theorem Ordinal.type_lift_preimage {α : Type u} {β : Type v} (r : α → α → Prop) [IsWellOrder α r] (f : β ≃ α) : Ordinal.lift.{u, v} (Ordinal.type (⇑f ⁻¹'o r)) = Ordinal.lift.{v, u} (Ordinal.type r)

@[simp]

theorem Ordinal.type_lift_preimage_aux {α : Type u} {β : Type v} (r : α → α → Prop) [IsWellOrder α r] (f : β ≃ α) : Ordinal.lift.{u, v} (Ordinal.type fun (x y : β) => r (f x) (f y)) = Ordinal.lift.{v, u} (Ordinal.type r)

theorem Ordinal.lift_umax : Ordinal.lift.{max u v, u} = Ordinal.lift.{v, u}

lift.{max u v, u} equals lift.{v, u}.

theorem Ordinal.lift_umax' : Ordinal.lift.{max v u, u} = Ordinal.lift.{v, u}

lift.{max v u, u} equals lift.{v, u}.

theorem Ordinal.lift_id' (a : Ordinal.{max u_3 u_4} ) : Ordinal.lift.{u_3, max u_3 u_4} a = a

An ordinal lifted to a lower or equal universe equals itself.

@[simp]

theorem Ordinal.lift_id (a : Ordinal.{u}) : Ordinal.lift.{u, u} a = a

An ordinal lifted to the same universe equals itself.

@[simp]

theorem Ordinal.lift_uzero (a : Ordinal.{u}) : Ordinal.lift.{0, u} a = a

An ordinal lifted to the zero universe equals itself.

@[simp]

theorem Ordinal.lift_lift (a : Ordinal.{u_3}) : Ordinal.lift.{w, max v u_3} (Ordinal.lift.{v, u_3} a) = Ordinal.lift.{max v w, u_3} a

theorem Ordinal.lift_type_le {α : Type u} {β : Type v} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] : Ordinal.lift.{max v w, u} (Ordinal.type r) ≤ Ordinal.lift.{max u w, v} (Ordinal.type s) ↔ Nonempty (r ≼i s)

theorem Ordinal.lift_type_eq {α : Type u} {β : Type v} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] : Ordinal.lift.{max v w, u} (Ordinal.type r) = Ordinal.lift.{max u w, v} (Ordinal.type s) ↔ Nonempty (r ≃r s)

theorem Ordinal.lift_type_lt {α : Type u} {β : Type v} {r : α → α → Prop} {s : β → β → Prop} [IsWellOrder α r] [IsWellOrder β s] : Ordinal.lift.{max v w, u} (Ordinal.type r) < Ordinal.lift.{max u w, v} (Ordinal.type s) ↔ Nonempty (r ≺i s)

@[simp]

theorem Ordinal.lift_le {a : Ordinal.{v}} {b : Ordinal.{v}} : Ordinal.lift.{u, v} a ≤ Ordinal.lift.{u, v} b ↔ a ≤ b

@[simp]

theorem Ordinal.lift_inj {a : Ordinal.{v}} {b : Ordinal.{v}} : Ordinal.lift.{u, v} a = Ordinal.lift.{u, v} b ↔ a = b

@[simp]

theorem Ordinal.lift_lt {a : Ordinal.{v}} {b : Ordinal.{v}} : Ordinal.lift.{u, v} a < Ordinal.lift.{u, v} b ↔ a < b

@[simp]

theorem Ordinal.lift_zero : Ordinal.lift.{u_4, u_3} 0 = 0

@[simp]

theorem Ordinal.lift_one : Ordinal.lift.{u_4, u_3} 1 = 1

@[simp]

theorem Ordinal.lift_card (a : Ordinal.{v}) : Cardinal.lift.{u, v} (Ordinal.card a) = Ordinal.card (Ordinal.lift.{u, v} a)

theorem Ordinal.lift_down' {a : Cardinal.{u}} {b : Ordinal.{max u v} } (h : Ordinal.card b ≤ Cardinal.lift.{v, u} a) : ∃ (a' : Ordinal.{u}), Ordinal.lift.{v, u} a' = b

theorem Ordinal.lift_down {a : Ordinal.{u}} {b : Ordinal.{max u v} } (h : b ≤ Ordinal.lift.{v, u} a) : ∃ (a' : Ordinal.{u}), Ordinal.lift.{v, u} a' = b

theorem Ordinal.le_lift_iff {a : Ordinal.{u}} {b : Ordinal.{max u v} } : b ≤ Ordinal.lift.{v, u} a ↔ ∃ (a' : Ordinal.{u}), Ordinal.lift.{v, u} a' = b ∧ a' ≤ a

theorem Ordinal.lt_lift_iff {a : Ordinal.{u}} {b : Ordinal.{max u v} } : b < Ordinal.lift.{v, u} a ↔ ∃ (a' : Ordinal.{u}), Ordinal.lift.{v, u} a' = b ∧ a' < a

def Ordinal.lift.initialSeg : (fun (x x_1 : Ordinal.{u}) => x < x_1) ≼i fun (x x_1 : Ordinal.{max u v} ) => x < x_1

Initial segment version of the lift operation on ordinals, embedding ordinal.{u} in ordinal.{v} as an initial segment when u ≤ v.

Equations

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

@[simp]

theorem Ordinal.lift.initialSeg_coe : ⇑Ordinal.lift.initialSeg = Ordinal.lift.{v, u}

The first infinite ordinal omega

def Ordinal.omega : Ordinal.{u}

ω is the first infinite ordinal, defined as the order type of ℕ.

Equations

• Ordinal.omega = Ordinal.lift.{u, 0} (Ordinal.type fun (x x_1 : ℕ) => x < x_1)

def Ordinal.termω : Lean.ParserDescr

ω is the first infinite ordinal, defined as the order type of ℕ.

Equations

• Ordinal.termω = Lean.ParserDescr.node `Ordinal.termω 1024 (Lean.ParserDescr.symbol "ω")

@[simp]

theorem Ordinal.type_nat_lt : (Ordinal.type fun (x x_1 : ℕ) => x < x_1) = Ordinal.omega

Note that the presence of this lemma makes simp [omega] form a loop.

@[simp]

theorem Ordinal.card_omega : Ordinal.card Ordinal.omega = Cardinal.aleph0

@[simp]

theorem Ordinal.lift_omega : Ordinal.lift.{u_3, u_4} Ordinal.omega = Ordinal.omega

Definition and first properties of addition on ordinals

In this paragraph, we introduce the addition on ordinals, and prove just enough properties to deduce that the order on ordinals is total (and therefore well-founded). Further properties of the addition, together with properties of the other operations, are proved in Mathlib/SetTheory/Ordinal/Arithmetic.lean.

instance Ordinal.add : Add Ordinal.{u}

o₁ + o₂ is the order on the disjoint union of o₁ and o₂ obtained by declaring that every element of o₁ is smaller than every element of o₂.

Equations

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

instance Ordinal.addMonoidWithOne : AddMonoidWithOne Ordinal.{u}

Equations

• Ordinal.addMonoidWithOne = AddMonoidWithOne.mk Ordinal.addMonoidWithOne.proof_6 Ordinal.addMonoidWithOne.proof_7

@[simp]

theorem Ordinal.card_add (o₁ : Ordinal.{u_3}) (o₂ : Ordinal.{u_3}) : Ordinal.card (o₁ + o₂) = Ordinal.card o₁ + Ordinal.card o₂

@[simp]

theorem Ordinal.type_sum_lex {α : Type u} {β : Type u} (r : α → α → Prop) (s : β → β → Prop) [IsWellOrder α r] [IsWellOrder β s] : Ordinal.type (Sum.Lex r s) = Ordinal.type r + Ordinal.type s

@[simp]

theorem Ordinal.card_nat (n : ℕ) : Ordinal.card ↑n = ↑n

@[simp]

theorem Ordinal.card_ofNat (n : ℕ) [Nat.AtLeastTwo n] : Ordinal.card (OfNat.ofNat n) = OfNat.ofNat n

instance Ordinal.add_covariantClass_le : CovariantClass Ordinal.{u} Ordinal.{u} (fun (x x_1 : Ordinal.{u}) => x + x_1) fun (x x_1 : Ordinal.{u}) => x ≤ x_1

Equations

• Ordinal.add_covariantClass_le = ⋯

instance Ordinal.add_swap_covariantClass_le : CovariantClass Ordinal.{u} Ordinal.{u} (Function.swap fun (x x_1 : Ordinal.{u}) => x + x_1) fun (x x_1 : Ordinal.{u}) => x ≤ x_1

Equations

• Ordinal.add_swap_covariantClass_le = ⋯

theorem Ordinal.le_add_right (a : Ordinal.{u_3}) (b : Ordinal.{u_3}) : a ≤ a + b

theorem Ordinal.le_add_left (a : Ordinal.{u_3}) (b : Ordinal.{u_3}) : a ≤ b + a

instance Ordinal.linearOrder : LinearOrder Ordinal.{u_3}

Equations

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

instance Ordinal.wellFoundedLT : WellFoundedLT Ordinal.{u_3}

Equations

• Ordinal.wellFoundedLT = ⋯

instance Ordinal.isWellOrder : IsWellOrder Ordinal.{u_3} fun (x x_1 : Ordinal.{u_3}) => x < x_1

Equations

• Ordinal.isWellOrder = ⋯

instance Ordinal.instConditionallyCompleteLinearOrderBotOrdinal : ConditionallyCompleteLinearOrderBot Ordinal.{u_3}

Equations

• Ordinal.instConditionallyCompleteLinearOrderBotOrdinal = IsWellOrder.conditionallyCompleteLinearOrderBot Ordinal.{u_3}

theorem Ordinal.max_zero_left (a : Ordinal.{u_3}) : max 0 a = a

theorem Ordinal.max_zero_right (a : Ordinal.{u_3}) : max a 0 = a

@[simp]

theorem Ordinal.max_eq_zero {a : Ordinal.{u_3}} {b : Ordinal.{u_3}} : max a b = 0 ↔ a = 0 ∧ b = 0

@[simp]

theorem Ordinal.sInf_empty : sInf ∅ = 0

Successor order properties

instance Ordinal.noMaxOrder : NoMaxOrder Ordinal.{u_3}

Equations

• Ordinal.noMaxOrder = ⋯

instance Ordinal.succOrder : SuccOrder Ordinal.{u}

Equations

• Ordinal.succOrder = SuccOrder.ofSuccLeIff (fun (o : Ordinal.{u}) => o + 1) ⋯

@[simp]

theorem Ordinal.add_one_eq_succ (o : Ordinal.{u_3}) : o + 1 = Order.succ o

@[simp]

theorem Ordinal.succ_zero : Order.succ 0 = 1

@[simp]

theorem Ordinal.succ_one : Order.succ 1 = 2

theorem Ordinal.add_succ (o₁ : Ordinal.{u_3}) (o₂ : Ordinal.{u_3}) : o₁ + Order.succ o₂ = Order.succ (o₁ + o₂)

theorem Ordinal.one_le_iff_pos {o : Ordinal.{u_3}} : 1 ≤ o ↔ 0 < o

theorem Ordinal.one_le_iff_ne_zero {o : Ordinal.{u_3}} : 1 ≤ o ↔ o ≠ 0

theorem Ordinal.succ_pos (o : Ordinal.{u_3}) : 0 < Order.succ o

theorem Ordinal.succ_ne_zero (o : Ordinal.{u_3}) : Order.succ o ≠ 0

@[simp]

theorem Ordinal.lt_one_iff_zero {a : Ordinal.{u_3}} : a < 1 ↔ a = 0

theorem Ordinal.le_one_iff {a : Ordinal.{u_3}} : a ≤ 1 ↔ a = 0 ∨ a = 1

@[simp]

theorem Ordinal.card_succ (o : Ordinal.{u_3}) : Ordinal.card (Order.succ o) = Ordinal.card o + 1

theorem Ordinal.natCast_succ (n : ℕ) : ↑(Nat.succ n) = Order.succ ↑n

instance Ordinal.uniqueIioOne : Unique ↑(Set.Iio 1)

Equations

• Ordinal.uniqueIioOne = { toInhabited := { default := { val := 0, property := Ordinal.uniqueIioOne.proof_1 } }, uniq := Ordinal.uniqueIioOne.proof_2 }

instance Ordinal.uniqueOutOne : Unique (Quotient.out 1).α

Equations

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

theorem Ordinal.one_out_eq (x : (Quotient.out 1).α) : x = Ordinal.enum (fun (x x_1 : (Quotient.out 1).α) => x < x_1) 0 ⋯

Extra properties of typein and enum

@[simp]

theorem Ordinal.typein_one_out (x : (Quotient.out 1).α) : Ordinal.typein (fun (x x_1 : (Quotient.out 1).α) => x < x_1) x = 0

@[simp]

theorem Ordinal.typein_le_typein {α : Type u} (r : α → α → Prop) [IsWellOrder α r] {x : α} {x' : α} : Ordinal.typein r x ≤ Ordinal.typein r x' ↔ ¬r x' x

theorem Ordinal.typein_le_typein' (o : Ordinal.{u_3}) {x : (Quotient.out o).α} {x' : (Quotient.out o).α} : Ordinal.typein (fun (x x_1 : (Quotient.out o).α) => x < x_1) x ≤ Ordinal.typein (fun (x x_1 : (Quotient.out o).α) => x < x_1) x' ↔ x ≤ x'

@[simp]

theorem Ordinal.enum_le_enum {α : Type u} (r : α → α → Prop) [IsWellOrder α r] {o : Ordinal.{u}} {o' : Ordinal.{u}} (ho : o < Ordinal.type r) (ho' : o' < Ordinal.type r) : ¬r (Ordinal.enum r o' ho') (Ordinal.enum r o ho) ↔ o ≤ o'

@[simp]

theorem Ordinal.enum_le_enum' (a : Ordinal.{u_3}) {o : Ordinal.{u_3}} {o' : Ordinal.{u_3}} (ho : o < Ordinal.type fun (x x_1 : (Quotient.out a).α) => x < x_1) (ho' : o' < Ordinal.type fun (x x_1 : (Quotient.out a).α) => x < x_1) : Ordinal.enum (fun (x x_1 : (Quotient.out a).α) => x < x_1) o ho ≤ Ordinal.enum (fun (x x_1 : (Quotient.out a).α) => x < x_1) o' ho' ↔ o ≤ o'

theorem Ordinal.enum_zero_le {α : Type u} {r : α → α → Prop} [IsWellOrder α r] (h0 : 0 < Ordinal.type r) (a : α) : ¬r a (Ordinal.enum r 0 h0)

theorem Ordinal.enum_zero_le' {o : Ordinal.{u_3}} (h0 : 0 < o) (a : (Quotient.out o).α) : Ordinal.enum (fun (x x_1 : (Quotient.out o).α) => x < x_1) 0 ⋯ ≤ a

theorem Ordinal.le_enum_succ {o : Ordinal.{u_3}} (a : (Quotient.out (Order.succ o)).α) : a ≤ Ordinal.enum (fun (x x_1 : (Quotient.out (Order.succ o)).α) => x < x_1) o ⋯

@[simp]

theorem Ordinal.enum_inj {α : Type u} {r : α → α → Prop} [IsWellOrder α r] {o₁ : Ordinal.{u}} {o₂ : Ordinal.{u}} (h₁ : o₁ < Ordinal.type r) (h₂ : o₂ < Ordinal.type r) : Ordinal.enum r o₁ h₁ = Ordinal.enum r o₂ h₂ ↔ o₁ = o₂

@[simp]

theorem Ordinal.enumIso_apply {α : Type u} (r : α → α → Prop) [IsWellOrder α r] (x : ↑fun (x : Ordinal.{u}) => x < Ordinal.type r) : (Ordinal.enumIso r) x = Ordinal.enum r ↑x ⋯

@[simp]

theorem Ordinal.enumIso_symm_apply_coe {α : Type u} (r : α → α → Prop) [IsWellOrder α r] (x : α) : ↑((RelIso.symm (Ordinal.enumIso r)) x) = Ordinal.typein r x

def Ordinal.enumIso {α : Type u} (r : α → α → Prop) [IsWellOrder α r] : (Subrel (fun (x x_1 : Ordinal.{u}) => x < x_1) fun (x : Ordinal.{u}) => x < Ordinal.type r) ≃r r

A well order r is order isomorphic to the set of ordinals smaller than type r.

Equations

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

@[simp]

theorem Ordinal.enumIsoOut_symm_apply_coe (o : Ordinal.{u_3}) (x : (Quotient.out o).α) : ↑((RelIso.symm (Ordinal.enumIsoOut o)) x) = Ordinal.typein (fun (x x_1 : (Quotient.out o).α) => x < x_1) x

@[simp]

theorem Ordinal.enumIsoOut_apply (o : Ordinal.{u_3}) (x : ↑(Set.Iio o)) : (Ordinal.enumIsoOut o) x = Ordinal.enum (fun (x x_1 : (Quotient.out o).α) => x < x_1) ↑x ⋯

noncomputable def Ordinal.enumIsoOut (o : Ordinal.{u_3}) : ↑(Set.Iio o) ≃o (Quotient.out o).α

The order isomorphism between ordinals less than o and o.out.α.

Equations

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

def Ordinal.outOrderBotOfPos {o : Ordinal.{u_3}} (ho : 0 < o) : OrderBot (Quotient.out o).α

o.out.α is an OrderBot whenever 0 < o.

Equations

• Ordinal.outOrderBotOfPos ho = OrderBot.mk ⋯

theorem Ordinal.enum_zero_eq_bot {o : Ordinal.{u_3}} (ho : 0 < o) : Ordinal.enum (fun (x x_1 : (Quotient.out o).α) => x < x_1) 0 ⋯ = ⊥

Universal ordinal

def Ordinal.univ : Ordinal.{max (u + 1) v}

univ.{u v} is the order type of the ordinals of Type u as a member of Ordinal.{v} (when u < v). It is an inaccessible cardinal.

Equations

• Ordinal.univ.{u, v} = Ordinal.lift.{v, u + 1} (Ordinal.type fun (x x_1 : Ordinal.{u}) => x < x_1)

theorem Ordinal.univ_id : Ordinal.univ.{u, u + 1} = Ordinal.type fun (x x_1 : Ordinal.{u}) => x < x_1

@[simp]

theorem Ordinal.lift_univ : Ordinal.lift.{w, max (u + 1) v} Ordinal.univ.{u, v} = Ordinal.univ.{u, max v w}

theorem Ordinal.univ_umax : Ordinal.univ.{u, max (u + 1) v} = Ordinal.univ.{u, v}

def Ordinal.lift.principalSeg : (fun (x x_1 : Ordinal.{u}) => x < x_1) ≺i fun (x x_1 : Ordinal.{max (u + 1) v} ) => x < x_1

Principal segment version of the lift operation on ordinals, embedding ordinal.{u} in ordinal.{v} as a principal segment when u < v.

Equations

• Ordinal.lift.principalSeg = { toRelEmbedding := Ordinal.lift.initialSeg.toRelEmbedding, top := Ordinal.univ.{u, v} , down' := Ordinal.lift.principalSeg.proof_1 }

@[simp]

theorem Ordinal.lift.principalSeg_coe : ⇑Ordinal.lift.principalSeg.toRelEmbedding = Ordinal.lift.{max (u + 1) v, u}

@[simp]

theorem Ordinal.lift.principalSeg_top : Ordinal.lift.principalSeg.top = Ordinal.univ.{u, v}

theorem Ordinal.lift.principalSeg_top' : Ordinal.lift.principalSeg.top = Ordinal.type fun (x x_1 : Ordinal.{u}) => x < x_1

Representing a cardinal with an ordinal

@[simp]

theorem Cardinal.mk_ordinal_out (o : Ordinal.{u_3}) : Cardinal.mk (Quotient.out o).α = Ordinal.card o

def Cardinal.ord (c : Cardinal.{u}) : Ordinal.{u}

The ordinal corresponding to a cardinal c is the least ordinal whose cardinal is c. For the order-embedding version, see ord.order_embedding.

Equations

• Cardinal.ord c = let F := fun (α : Type u) => ⨅ (r : { r : α → α → Prop // IsWellOrder α r }), Ordinal.type ↑r; Quot.liftOn c F Cardinal.ord.proof_2

theorem Cardinal.ord_eq_Inf (α : Type u) : Cardinal.ord (Cardinal.mk α) = ⨅ (r : { r : α → α → Prop // IsWellOrder α r }), Ordinal.type ↑r

theorem Cardinal.ord_eq (α : Type u_3) : ∃ (r : α → α → Prop) (wo : IsWellOrder α r), Cardinal.ord (Cardinal.mk α) = Ordinal.type r

theorem Cardinal.ord_le_type {α : Type u} (r : α → α → Prop) [h : IsWellOrder α r] : Cardinal.ord (Cardinal.mk α) ≤ Ordinal.type r

theorem Cardinal.ord_le {c : Cardinal.{u_3}} {o : Ordinal.{u_3}} : Cardinal.ord c ≤ o ↔ c ≤ Ordinal.card o

theorem Cardinal.gc_ord_card : GaloisConnection Cardinal.ord Ordinal.card

theorem Cardinal.lt_ord {c : Cardinal.{u_3}} {o : Ordinal.{u_3}} : o < Cardinal.ord c ↔ Ordinal.card o < c

@[simp]

theorem Cardinal.card_ord (c : Cardinal.{u_3}) : Ordinal.card (Cardinal.ord c) = c

def Cardinal.gciOrdCard : GaloisCoinsertion Cardinal.ord Ordinal.card

Galois coinsertion between Cardinal.ord and Ordinal.card.

Equations

• Cardinal.gciOrdCard = GaloisConnection.toGaloisCoinsertion Cardinal.gc_ord_card Cardinal.gciOrdCard.proof_1

theorem Cardinal.ord_card_le (o : Ordinal.{u_3}) : Cardinal.ord (Ordinal.card o) ≤ o

theorem Cardinal.lt_ord_succ_card (o : Ordinal.{u_3}) : o < Cardinal.ord (Order.succ (Ordinal.card o))

theorem Cardinal.card_le_iff {o : Ordinal.{u_3}} {c : Cardinal.{u_3}} : Ordinal.card o ≤ c ↔ o < Cardinal.ord (Order.succ c)

theorem Cardinal.card_le_of_le_ord {o : Ordinal.{u_3}} {c : Cardinal.{u_3}} (ho : o ≤ Cardinal.ord c) : Ordinal.card o ≤ c

A variation on Cardinal.lt_ord using ≤: If o is no greater than the initial ordinal of cardinality c, then its cardinal is no greater than c.

The converse, however, is false (for instance, o = ω+1 and c = ℵ₀).

theorem Cardinal.ord_strictMono : StrictMono Cardinal.ord

theorem Cardinal.ord_mono : Monotone Cardinal.ord

@[simp]

theorem Cardinal.ord_le_ord {c₁ : Cardinal.{u_3}} {c₂ : Cardinal.{u_3}} : Cardinal.ord c₁ ≤ Cardinal.ord c₂ ↔ c₁ ≤ c₂

@[simp]

theorem Cardinal.ord_lt_ord {c₁ : Cardinal.{u_3}} {c₂ : Cardinal.{u_3}} : Cardinal.ord c₁ < Cardinal.ord c₂ ↔ c₁ < c₂

@[simp]

theorem Cardinal.ord_zero : Cardinal.ord 0 = 0

@[simp]

theorem Cardinal.ord_nat (n : ℕ) : Cardinal.ord ↑n = ↑n

@[simp]

theorem Cardinal.ord_one : Cardinal.ord 1 = 1

@[simp]

theorem Cardinal.ord_ofNat (n : ℕ) [Nat.AtLeastTwo n] : Cardinal.ord (OfNat.ofNat n) = OfNat.ofNat n

@[simp]

theorem Cardinal.lift_ord (c : Cardinal.{v}) : Ordinal.lift.{u, v} (Cardinal.ord c) = Cardinal.ord (Cardinal.lift.{u, v} c)

theorem Cardinal.mk_ord_out (c : Cardinal.{u_3}) : Cardinal.mk (Quotient.out (Cardinal.ord c)).α = c

theorem Cardinal.card_typein_lt {α : Type u} (r : α → α → Prop) [IsWellOrder α r] (x : α) (h : Cardinal.ord (Cardinal.mk α) = Ordinal.type r) : Ordinal.card (Ordinal.typein r x) < Cardinal.mk α

theorem Cardinal.card_typein_out_lt (c : Cardinal.{u_3}) (x : (Quotient.out (Cardinal.ord c)).α) : Ordinal.card (Ordinal.typein (fun (x x_1 : (Quotient.out (Cardinal.ord c)).α) => x < x_1) x) < c

theorem Cardinal.ord_injective : Function.Injective Cardinal.ord

def Cardinal.ord.orderEmbedding : Cardinal.{u_3} ↪o Ordinal.{u_3}

The ordinal corresponding to a cardinal c is the least ordinal whose cardinal is c. This is the order-embedding version. For the regular function, see ord.

Equations

• Cardinal.ord.orderEmbedding = RelEmbedding.orderEmbeddingOfLTEmbedding (RelEmbedding.ofMonotone Cardinal.ord Cardinal.ord.orderEmbedding.proof_2)

@[simp]

theorem Cardinal.ord.orderEmbedding_coe : ⇑Cardinal.ord.orderEmbedding = Cardinal.ord

def Cardinal.univ : Cardinal.{max (u + 1) v}

The cardinal univ is the cardinality of ordinal univ, or equivalently the cardinal of Ordinal.{u}, or Cardinal.{u}, as an element of Cardinal.{v} (when u < v).

Equations

• Cardinal.univ.{u, v} = Cardinal.lift.{v, u + 1} (Cardinal.mk Ordinal.{u})

theorem Cardinal.univ_id : Cardinal.univ.{u, u + 1} = Cardinal.mk Ordinal.{u}

@[simp]

theorem Cardinal.lift_univ : Cardinal.lift.{w, max (u + 1) v} Cardinal.univ.{u, v} = Cardinal.univ.{u, max v w}

theorem Cardinal.univ_umax : Cardinal.univ.{u, max (u + 1) v} = Cardinal.univ.{u, v}

theorem Cardinal.lift_lt_univ (c : Cardinal.{u}) : Cardinal.lift.{u + 1, u} c < Cardinal.univ.{u, u + 1}

theorem Cardinal.lift_lt_univ' (c : Cardinal.{u}) : Cardinal.lift.{max (u + 1) v, u} c < Cardinal.univ.{u, v}

@[simp]

theorem Cardinal.ord_univ : Cardinal.ord Cardinal.univ.{u, v} = Ordinal.univ.{u, v}

theorem Cardinal.lt_univ {c : Cardinal.{u + 1} } : c < Cardinal.univ.{u, u + 1} ↔ ∃ (c' : Cardinal.{u}), c = Cardinal.lift.{u + 1, u} c'

theorem Cardinal.lt_univ' {c : Cardinal.{max (u + 1) v} } : c < Cardinal.univ.{u, v} ↔ ∃ (c' : Cardinal.{u}), c = Cardinal.lift.{max (u + 1) v, u} c'

theorem Cardinal.small_iff_lift_mk_lt_univ {α : Type u} : Small.{v, u} α ↔ Cardinal.lift.{v + 1, u} (Cardinal.mk α) < Cardinal.univ.{v, max u (v + 1)}

@[simp]

theorem Ordinal.card_univ : Ordinal.card Ordinal.univ.{u, v} = Cardinal.univ.{u, v}

@[simp]

theorem Ordinal.nat_le_card {o : Ordinal.{u_3}} {n : ℕ} : ↑n ≤ Ordinal.card o ↔ ↑n ≤ o

@[simp]

theorem Ordinal.one_le_card {o : Ordinal.{u_3}} : 1 ≤ Ordinal.card o ↔ 1 ≤ o

@[simp]

theorem Ordinal.ofNat_le_card {o : Ordinal.{u_3}} {n : ℕ} [Nat.AtLeastTwo n] : OfNat.ofNat n ≤ Ordinal.card o ↔ OfNat.ofNat n ≤ o

@[simp]

theorem Ordinal.nat_lt_card {o : Ordinal.{u_3}} {n : ℕ} : ↑n < Ordinal.card o ↔ ↑n < o

@[simp]

theorem Ordinal.zero_lt_card {o : Ordinal.{u_3}} : 0 < Ordinal.card o ↔ 0 < o

@[simp]

theorem Ordinal.one_lt_card {o : Ordinal.{u_3}} : 1 < Ordinal.card o ↔ 1 < o

@[simp]

theorem Ordinal.ofNat_lt_card {o : Ordinal.{u_3}} {n : ℕ} [Nat.AtLeastTwo n] : OfNat.ofNat n < Ordinal.card o ↔ OfNat.ofNat n < o

@[simp]

theorem Ordinal.card_lt_nat {o : Ordinal.{u_3}} {n : ℕ} : Ordinal.card o < ↑n ↔ o < ↑n

@[simp]

theorem Ordinal.card_lt_ofNat {o : Ordinal.{u_3}} {n : ℕ} [Nat.AtLeastTwo n] : Ordinal.card o < OfNat.ofNat n ↔ o < OfNat.ofNat n

@[simp]

theorem Ordinal.card_le_nat {o : Ordinal.{u_3}} {n : ℕ} : Ordinal.card o ≤ ↑n ↔ o ≤ ↑n

@[simp]

theorem Ordinal.card_le_one {o : Ordinal.{u_3}} : Ordinal.card o ≤ 1 ↔ o ≤ 1

@[simp]

theorem Ordinal.card_le_ofNat {o : Ordinal.{u_3}} {n : ℕ} [Nat.AtLeastTwo n] : Ordinal.card o ≤ OfNat.ofNat n ↔ o ≤ OfNat.ofNat n

@[simp]

theorem Ordinal.card_eq_nat {o : Ordinal.{u_3}} {n : ℕ} : Ordinal.card o = ↑n ↔ o = ↑n

@[simp]

theorem Ordinal.card_eq_zero {o : Ordinal.{u_3}} : Ordinal.card o = 0 ↔ o = 0

@[simp]

theorem Ordinal.card_eq_one {o : Ordinal.{u_3}} : Ordinal.card o = 1 ↔ o = 1

@[simp]

theorem Ordinal.card_eq_ofNat {o : Ordinal.{u_3}} {n : ℕ} [Nat.AtLeastTwo n] : Ordinal.card o = OfNat.ofNat n ↔ o = OfNat.ofNat n

@[simp]

theorem Ordinal.type_fintype {α : Type u} (r : α → α → Prop) [IsWellOrder α r] [Fintype α] : Ordinal.type r = ↑(Fintype.card α)

theorem Ordinal.type_fin (n : ℕ) : (Ordinal.type fun (x x_1 : Fin n) => x < x_1) = ↑n

Sorted lists

theorem List.Sorted.lt_ord_of_lt {α : Type u} [LinearOrder α] [IsWellOrder α fun (x x_1 : α) => x < x_1] {l : List α} {m : List α} {o : Ordinal.{u}} (hl : List.Sorted (fun (x x_1 : α) => x > x_1) l) (hm : List.Sorted (fun (x x_1 : α) => x > x_1) m) (hmltl : m < l) (hlt : ∀ i ∈ l, Ordinal.typein (fun (x x_1 : α) => x < x_1) i < o) (i : α) : i ∈ m → Ordinal.typein (fun (x x_1 : α) => x < x_1) i < o