Projection of a line onto a closed interval

Given a linearly ordered type α, in this file we define

• Set.projIci (a : α) to be the map α → [a, ∞) sending (-∞, a] to a, and each point x ∈ [a, ∞) to itself;
• Set.projIic (b : α) to be the map α → (-∞, b[ sending [b, ∞) to b, and each point x ∈ (-∞, b] to itself;
• Set.projIcc (a b : α) (h : a ≤ b) to be the map α → [a, b] sending (-∞, a] to a, [b, ∞) to b, and each point x ∈ [a, b] to itself;
• Set.IccExtend {a b : α} (h : a ≤ b) (f : Icc a b → β) to be the extension of f to α defined as f ∘ projIcc a b h.
• Set.IciExtend {a : α} (f : Ici a → β) to be the extension of f to α defined as f ∘ projIci a.
• Set.IicExtend {b : α} (f : Iic b → β) to be the extension of f to α defined as f ∘ projIic b.

We also prove some trivial properties of these maps.

def Set.projIci {α : Type u_1} [LinearOrder α] (a x : α) : ↑(Ici a)

Projection of α to the closed interval [a, ∞).

Equations

• Set.projIci a x = ⟨max a x, ⋯⟩

def Set.projIic {α : Type u_1} [LinearOrder α] (b x : α) : ↑(Iic b)

Projection of α to the closed interval (-∞, b].

Equations

• Set.projIic b x = ⟨min b x, ⋯⟩

def Set.projIcc {α : Type u_1} [LinearOrder α] (a b : α) (h : a ≤ b) (x : α) : ↑(Icc a b)

Projection of α to the closed interval [a, b].

Equations

• Set.projIcc a b h x = ⟨max a (min b x), ⋯⟩

theorem Set.coe_projIci {α : Type u_1} [LinearOrder α] (a x : α) : ↑(projIci a x) = max a x

theorem Set.coe_projIic {α : Type u_1} [LinearOrder α] (b x : α) : ↑(projIic b x) = min b x

theorem Set.coe_projIcc {α : Type u_1} [LinearOrder α] (a b : α) (h : a ≤ b) (x : α) : ↑(projIcc a b h x) = max a (min b x)

theorem Set.projIci_of_le {α : Type u_1} [LinearOrder α] {a x : α} (hx : x ≤ a) : projIci a x = ⟨a, ⋯⟩

theorem Set.projIic_of_le {α : Type u_1} [LinearOrder α] {b x : α} (hx : b ≤ x) : projIic b x = ⟨b, ⋯⟩

theorem Set.projIcc_of_le_left {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) {x : α} (hx : x ≤ a) : projIcc a b h x = ⟨a, ⋯⟩

theorem Set.projIcc_of_right_le {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) {x : α} (hx : b ≤ x) : projIcc a b h x = ⟨b, ⋯⟩

@[simp]

theorem Set.projIci_self {α : Type u_1} [LinearOrder α] (a : α) : projIci a a = ⟨a, ⋯⟩

@[simp]

theorem Set.projIic_self {α : Type u_1} [LinearOrder α] (b : α) : projIic b b = ⟨b, ⋯⟩

@[simp]

theorem Set.projIcc_left {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) : projIcc a b h a = ⟨a, ⋯⟩

@[simp]

theorem Set.projIcc_right {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) : projIcc a b h b = ⟨b, ⋯⟩

theorem Set.projIci_eq_self {α : Type u_1} [LinearOrder α] {a x : α} : projIci a x = ⟨a, ⋯⟩ ↔ x ≤ a

theorem Set.projIic_eq_self {α : Type u_1} [LinearOrder α] {b x : α} : projIic b x = ⟨b, ⋯⟩ ↔ b ≤ x

theorem Set.projIcc_eq_left {α : Type u_1} [LinearOrder α] {a b x : α} (h : a < b) : projIcc a b ⋯ x = ⟨a, ⋯⟩ ↔ x ≤ a

theorem Set.projIcc_eq_right {α : Type u_1} [LinearOrder α] {a b x : α} (h : a < b) : projIcc a b ⋯ x = ⟨b, ⋯⟩ ↔ b ≤ x

theorem Set.projIci_of_mem {α : Type u_1} [LinearOrder α] {a x : α} (hx : x ∈ Ici a) : projIci a x = ⟨x, hx⟩

theorem Set.projIic_of_mem {α : Type u_1} [LinearOrder α] {b x : α} (hx : x ∈ Iic b) : projIic b x = ⟨x, hx⟩

theorem Set.projIcc_of_mem {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) {x : α} (hx : x ∈ Icc a b) : projIcc a b h x = ⟨x, hx⟩

@[simp]

theorem Set.projIci_coe {α : Type u_1} [LinearOrder α] {a : α} (x : ↑(Ici a)) : projIci a ↑x = x

@[simp]

theorem Set.projIic_coe {α : Type u_1} [LinearOrder α] {b : α} (x : ↑(Iic b)) : projIic b ↑x = x

@[simp]

theorem Set.projIcc_val {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) (x : ↑(Icc a b)) : projIcc a b h ↑x = x

theorem Set.projIci_surjOn {α : Type u_1} [LinearOrder α] {a : α} : SurjOn (projIci a) (Ici a) univ

theorem Set.projIic_surjOn {α : Type u_1} [LinearOrder α] {b : α} : SurjOn (projIic b) (Iic b) univ

theorem Set.projIcc_surjOn {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) : SurjOn (projIcc a b h) (Icc a b) univ

theorem Set.projIci_surjective {α : Type u_1} [LinearOrder α] {a : α} : Function.Surjective (projIci a)

theorem Set.projIic_surjective {α : Type u_1} [LinearOrder α] {b : α} : Function.Surjective (projIic b)

theorem Set.projIcc_surjective {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) : Function.Surjective (projIcc a b h)

@[simp]

theorem Set.range_projIci {α : Type u_1} [LinearOrder α] {a : α} : range (projIci a) = univ

@[simp]

theorem Set.range_projIic {α : Type u_1} [LinearOrder α] {a : α} : range (projIic a) = univ

@[simp]

theorem Set.range_projIcc {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) : range (projIcc a b h) = univ

theorem Set.monotone_projIci {α : Type u_1} [LinearOrder α] {a : α} : Monotone (projIci a)

theorem Set.monotone_projIic {α : Type u_1} [LinearOrder α] {a : α} : Monotone (projIic a)

theorem Set.monotone_projIcc {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) : Monotone (projIcc a b h)

theorem Set.strictMonoOn_projIci {α : Type u_1} [LinearOrder α] {a : α} : StrictMonoOn (projIci a) (Ici a)

theorem Set.strictMonoOn_projIic {α : Type u_1} [LinearOrder α] {b : α} : StrictMonoOn (projIic b) (Iic b)

theorem Set.strictMonoOn_projIcc {α : Type u_1} [LinearOrder α] {a b : α} (h : a ≤ b) : StrictMonoOn (projIcc a b h) (Icc a b)

def Set.IciExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] {a : α} (f : ↑(Ici a) → β) : α → β

Extend a function [a, ∞) → β to a map α → β.

Equations

• Set.IciExtend f = f ∘ Set.projIci a

def Set.IicExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] {b : α} (f : ↑(Iic b) → β) : α → β

Extend a function (-∞, b] → β to a map α → β.

Equations

• Set.IicExtend f = f ∘ Set.projIic b

def Set.IccExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) (f : ↑(Icc a b) → β) : α → β

Extend a function [a, b] → β to a map α → β.

Equations

• Set.IccExtend h f = f ∘ Set.projIcc a b h

theorem Set.IciExtend_apply {α : Type u_1} {β : Type u_2} [LinearOrder α] {a : α} (f : ↑(Ici a) → β) (x : α) : IciExtend f x = f ⟨max a x, ⋯⟩

theorem Set.IicExtend_apply {α : Type u_1} {β : Type u_2} [LinearOrder α] {b : α} (f : ↑(Iic b) → β) (x : α) : IicExtend f x = f ⟨min b x, ⋯⟩

theorem Set.IccExtend_apply {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) (f : ↑(Icc a b) → β) (x : α) : IccExtend h f x = f ⟨max a (min b x), ⋯⟩

@[simp]

theorem Set.range_IciExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] {a : α} (f : ↑(Ici a) → β) : range (IciExtend f) = range f

@[simp]

theorem Set.range_IicExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] {b : α} (f : ↑(Iic b) → β) : range (IicExtend f) = range f

@[simp]

theorem Set.IccExtend_range {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) (f : ↑(Icc a b) → β) : range (IccExtend h f) = range f

theorem Set.IciExtend_of_le {α : Type u_1} {β : Type u_2} [LinearOrder α] {a x : α} (f : ↑(Ici a) → β) (hx : x ≤ a) : IciExtend f x = f ⟨a, ⋯⟩

theorem Set.IicExtend_of_le {α : Type u_1} {β : Type u_2} [LinearOrder α] {b x : α} (f : ↑(Iic b) → β) (hx : b ≤ x) : IicExtend f x = f ⟨b, ⋯⟩

theorem Set.IccExtend_of_le_left {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) {x : α} (f : ↑(Icc a b) → β) (hx : x ≤ a) : IccExtend h f x = f ⟨a, ⋯⟩

theorem Set.IccExtend_of_right_le {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) {x : α} (f : ↑(Icc a b) → β) (hx : b ≤ x) : IccExtend h f x = f ⟨b, ⋯⟩

@[simp]

theorem Set.IciExtend_self {α : Type u_1} {β : Type u_2} [LinearOrder α] {a : α} (f : ↑(Ici a) → β) : IciExtend f a = f ⟨a, ⋯⟩

@[simp]

theorem Set.IicExtend_self {α : Type u_1} {β : Type u_2} [LinearOrder α] {b : α} (f : ↑(Iic b) → β) : IicExtend f b = f ⟨b, ⋯⟩

@[simp]

theorem Set.IccExtend_left {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) (f : ↑(Icc a b) → β) : IccExtend h f a = f ⟨a, ⋯⟩

@[simp]

theorem Set.IccExtend_right {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) (f : ↑(Icc a b) → β) : IccExtend h f b = f ⟨b, ⋯⟩

theorem Set.IciExtend_of_mem {α : Type u_1} {β : Type u_2} [LinearOrder α] {a x : α} (f : ↑(Ici a) → β) (hx : x ∈ Ici a) : IciExtend f x = f ⟨x, hx⟩

theorem Set.IicExtend_of_mem {α : Type u_1} {β : Type u_2} [LinearOrder α] {b x : α} (f : ↑(Iic b) → β) (hx : x ∈ Iic b) : IicExtend f x = f ⟨x, hx⟩

theorem Set.IccExtend_of_mem {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) {x : α} (f : ↑(Icc a b) → β) (hx : x ∈ Icc a b) : IccExtend h f x = f ⟨x, hx⟩

@[simp]

theorem Set.IciExtend_coe {α : Type u_1} {β : Type u_2} [LinearOrder α] {a : α} (f : ↑(Ici a) → β) (x : ↑(Ici a)) : IciExtend f ↑x = f x

@[simp]

theorem Set.IicExtend_coe {α : Type u_1} {β : Type u_2} [LinearOrder α] {b : α} (f : ↑(Iic b) → β) (x : ↑(Iic b)) : IicExtend f ↑x = f x

@[simp]

theorem Set.IccExtend_val {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) (f : ↑(Icc a b) → β) (x : ↑(Icc a b)) : IccExtend h f ↑x = f x

theorem Set.IccExtend_eq_self {α : Type u_1} {β : Type u_2} [LinearOrder α] {a b : α} (h : a ≤ b) (f : α → β) (ha : ∀ x < a, f x = f a) (hb : ∀ (x : α), b < x → f x = f b) : IccExtend h (f ∘ Subtype.val) = f

If f : α → β is a constant both on $(-∞, a]$ and on $[b, +∞)$, then the extension of this function from $[a, b]$ to the whole line is equal to the original function.

theorem Monotone.IciExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] [Preorder β] {a : α} {f : ↑(Set.Ici a) → β} (hf : Monotone f) : Monotone (Set.IciExtend f)

theorem Monotone.IicExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] [Preorder β] {b : α} {f : ↑(Set.Iic b) → β} (hf : Monotone f) : Monotone (Set.IicExtend f)

theorem Monotone.IccExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] [Preorder β] {a b : α} (h : a ≤ b) {f : ↑(Set.Icc a b) → β} (hf : Monotone f) : Monotone (Set.IccExtend h f)

theorem StrictMono.strictMonoOn_IciExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] [Preorder β] {a : α} {f : ↑(Set.Ici a) → β} (hf : StrictMono f) : StrictMonoOn (Set.IciExtend f) (Set.Ici a)

theorem StrictMono.strictMonoOn_IicExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] [Preorder β] {b : α} {f : ↑(Set.Iic b) → β} (hf : StrictMono f) : StrictMonoOn (Set.IicExtend f) (Set.Iic b)

theorem StrictMono.strictMonoOn_IccExtend {α : Type u_1} {β : Type u_2} [LinearOrder α] [Preorder β] {a b : α} (h : a ≤ b) {f : ↑(Set.Icc a b) → β} (hf : StrictMono f) : StrictMonoOn (Set.IccExtend h f) (Set.Icc a b)

theorem Set.OrdConnected.IciExtend {α : Type u_1} [LinearOrder α] {a : α} {s : Set ↑(Ici a)} (hs : s.OrdConnected) : {x : α | IciExtend (fun (x : ↑(Ici a)) => x ∈ s) x}.OrdConnected

theorem Set.OrdConnected.IicExtend {α : Type u_1} [LinearOrder α] {b : α} {s : Set ↑(Iic b)} (hs : s.OrdConnected) : {x : α | IicExtend (fun (x : ↑(Iic b)) => x ∈ s) x}.OrdConnected

theorem Set.OrdConnected.domRestrict {α : Type u_1} [LinearOrder α] {s t : Set α} (hs : s.OrdConnected) : {x : ↑t | t.domRestrict (fun (x : α) => x ∈ s) x}.OrdConnected

@[deprecated Set.OrdConnected.domRestrict (since := "2026-07-19")]

theorem Set.OrdConnected.restrict {α : Type u_1} [LinearOrder α] {s t : Set α} (hs : s.OrdConnected) : {x : ↑t | t.domRestrict (fun (x : α) => x ∈ s) x}.OrdConnected

Alias of Set.OrdConnected.domRestrict.