Nucleus

Locales are the dual concept to frames. Locale theory is a branch of point-free topology, where intuitively locales are like topological spaces which may or may not have enough points. Sublocales of a locale generalize the concept of subspaces in topology to the point-free setting.

A nucleus is an endomorphism of a frame which corresponds to a sublocale.

References

https://ncatlab.org/nlab/show/sublocale https://ncatlab.org/nlab/show/nucleus

structure Nucleus (X : Type u_2) [SemilatticeInf X] extends InfHom X X : Type u_2

A nucleus is an inflationary idempotent inf-preserving endomorphism of a semilattice. In a frame, nuclei correspond to sublocales.

• toFun : X → X
• map_inf' (a b : X) : self.toFun (a ⊓ b) = self.toFun a ⊓ self.toFun b
• idempotent' (x : X) : self.toFun (self.toFun x) ≤ self.toFun x

  A Nucleus is idempotent.

  Do not use this directly. Instead use NucleusClass.idempotent.

• le_apply' (x : X) : x ≤ self.toFun x

  A Nucleus is increasing.

  Do not use this directly. Instead use NucleusClass.le_apply.

class NucleusClass (F : Type u_2) (X : Type u_3) [SemilatticeInf X] [FunLike F X X] extends InfHomClass F X X : Prop

NucleusClass F X states that F is a type of nuclei.

• map_inf (f : F) (a b : X) : f (a ⊓ b) = f a ⊓ f b
• idempotent (x : X) (f : F) : f (f x) ≤ f x

  A nucleus is idempotent.

• le_apply (x : X) (f : F) : x ≤ f x

  A nucleus is increasing.

instance Nucleus.instFunLike {X : Type u_1} [CompleteLattice X] : FunLike (Nucleus X) X X

Equations

• Nucleus.instFunLike = { coe := fun (x : Nucleus X) => x.toFun, coe_injective' := ⋯ }

theorem Nucleus.toFun_eq_coe {X : Type u_1} [CompleteLattice X] (n : Nucleus X) : n.toFun = ⇑n

@[simp]

theorem Nucleus.coe_toInfHom {X : Type u_1} [CompleteLattice X] (n : Nucleus X) : ⇑n.toInfHom = ⇑n

@[simp]

theorem Nucleus.coe_mk {X : Type u_1} [CompleteLattice X] (f : InfHom X X) (h1 : ∀ (x : X), f.toFun (f.toFun x) ≤ f.toFun x) (h2 : ∀ (x : X), x ≤ f.toFun x) : ⇑{ toInfHom := f, idempotent' := h1, le_apply' := h2 } = ⇑f

instance Nucleus.instNucleusClass {X : Type u_1} [CompleteLattice X] : NucleusClass (Nucleus X) X

def Nucleus.toClosureOperator {X : Type u_1} [CompleteLattice X] (n : Nucleus X) : ClosureOperator X

Every Nucleus is a ClosureOperator.

Equations

• n.toClosureOperator = ClosureOperator.mk' ⇑n ⋯ ⋯ ⋯

theorem Nucleus.idempotent {X : Type u_1} [CompleteLattice X] {n : Nucleus X} {x : X} : n (n x) = n x

theorem Nucleus.le_apply {X : Type u_1} [CompleteLattice X] {n : Nucleus X} {x : X} : x ≤ n x

theorem Nucleus.map_inf {X : Type u_1} [CompleteLattice X] {n : Nucleus X} {x y : X} : n (x ⊓ y) = n x ⊓ n y

theorem Nucleus.ext {X : Type u_1} [CompleteLattice X] {m n : Nucleus X} (h : ∀ (a : X), m a = n a) : m = n

instance Nucleus.instTopHomClass {X : Type u_1} [CompleteLattice X] : TopHomClass (Nucleus X) X X

A Nucleus preserves ⊤.

instance Nucleus.instPartialOrder {X : Type u_1} [CompleteLattice X] : PartialOrder (Nucleus X)

Equations

• Nucleus.instPartialOrder = PartialOrder.lift DFunLike.coe ⋯

@[simp]

theorem Nucleus.coe_le_coe {X : Type u_1} [CompleteLattice X] {n m : Nucleus X} : ⇑m ≤ ⇑n ↔ m ≤ n

@[simp]

theorem Nucleus.coe_lt_coe {X : Type u_1} [CompleteLattice X] {n m : Nucleus X} : ⇑m < ⇑n ↔ m < n

instance Nucleus.instBot {X : Type u_1} [CompleteLattice X] : Bot (Nucleus X)

The smallest Nucleus is the identity.

Equations

• Nucleus.instBot = { bot := { toFun := fun (x : X) => x, map_inf' := ⋯, idempotent' := ⋯, le_apply' := ⋯ } }

instance Nucleus.instTop {X : Type u_1} [CompleteLattice X] : Top (Nucleus X)

The biggest Nucleus sends everything to ⊤.

Equations

• Nucleus.instTop = { top := { toFun := ⊤, map_inf' := ⋯, idempotent' := ⋯, le_apply' := ⋯ } }

@[simp]

theorem Nucleus.coe_bot {X : Type u_1} [CompleteLattice X] : ⇑⊥ = id

@[simp]

theorem Nucleus.coe_top {X : Type u_1} [CompleteLattice X] : ⇑⊤ = ⊤

@[simp]

theorem Nucleus.bot_apply {X : Type u_1} [CompleteLattice X] (x : X) : ⊥ x = x

@[simp]

theorem Nucleus.top_apply {X : Type u_1} [CompleteLattice X] (x : X) : ⊤ x = ⊤

instance Nucleus.instBoundedOrder {X : Type u_1} [CompleteLattice X] : BoundedOrder (Nucleus X)

Equations

• Nucleus.instBoundedOrder = BoundedOrder.mk