Closure operators on large locales

Content created by Egbert Rijke, Fredrik Bakke, Julian KG, Maša Žaucer, fernabnor, Gregor Perčič and louismntnu.

Created on 2023-06-08.
Last modified on 2023-11-24.

module order-theory.closure-operators-large-locales where
Imports
open import foundation.action-on-identifications-functions
open import foundation.dependent-pair-types
open import foundation.function-types
open import foundation.identity-types
open import foundation.large-binary-relations
open import foundation.logical-equivalences
open import foundation.propositions
open import foundation.sets
open import foundation.subtypes
open import foundation.universe-levels

open import order-theory.closure-operators-large-posets
open import order-theory.large-frames
open import order-theory.large-locales
open import order-theory.large-meet-semilattices
open import order-theory.large-meet-subsemilattices
open import order-theory.large-posets
open import order-theory.large-subposets
open import order-theory.large-subpreorders
open import order-theory.large-suplattices
open import order-theory.least-upper-bounds-large-posets
open import order-theory.order-preserving-maps-large-posets

Idea

A closure operator on a large locale L is a closure operator on the underlying large poset of L.

We show that if the closed elements are closed under meets, then the closed elements form a large locale. Note that the condition that the closed elements are closed under meets is more general than the condition that the closure operator is a nucleus.

Definitions

Closure operators on large locales

module _
  {α : Level  Level} {β : Level  Level  Level} {γ : Level}
  (L : Large-Locale α β γ)
  where

  closure-operator-Large-Locale : UUω
  closure-operator-Large-Locale =
    closure-operator-Large-Poset (large-poset-Large-Locale L)

  module _
    (j : closure-operator-Large-Locale)
    where

    hom-large-poset-closure-operator-Large-Locale :
      hom-Large-Poset
        ( λ l  l)
        ( large-poset-Large-Locale L)
        ( large-poset-Large-Locale L)
    hom-large-poset-closure-operator-Large-Locale =
      hom-closure-operator-Large-Poset j

    map-closure-operator-Large-Locale :
      {l1 : Level}  type-Large-Locale L l1  type-Large-Locale L l1
    map-closure-operator-Large-Locale =
      map-hom-Large-Poset
        ( large-poset-Large-Locale L)
        ( large-poset-Large-Locale L)
        ( hom-large-poset-closure-operator-Large-Locale)

    preserves-order-closure-operator-Large-Locale :
      {l1 l2 : Level}
      (x : type-Large-Locale L l1)
      (y : type-Large-Locale L l2) 
      leq-Large-Locale L x y 
      leq-Large-Locale L
        ( map-closure-operator-Large-Locale x)
        ( map-closure-operator-Large-Locale y)
    preserves-order-closure-operator-Large-Locale =
      preserves-order-hom-Large-Poset
        ( large-poset-Large-Locale L)
        ( large-poset-Large-Locale L)
        ( hom-large-poset-closure-operator-Large-Locale)

    is-inflationary-closure-operator-Large-Locale :
      {l1 : Level} (x : type-Large-Locale L l1) 
      leq-Large-Locale L x
        ( map-closure-operator-Large-Locale x)
    is-inflationary-closure-operator-Large-Locale =
      is-inflationary-closure-operator-Large-Poset j

    is-idempotent-closure-operator-Large-Locale :
      {l1 : Level} (x : type-Large-Locale L l1) 
      map-closure-operator-Large-Locale
        ( map-closure-operator-Large-Locale x) 
      map-closure-operator-Large-Locale x
    is-idempotent-closure-operator-Large-Locale =
      is-idempotent-closure-operator-Large-Poset j

The large suplattice of j-closed elements of a closure operator

module _
  {α : Level  Level} {β : Level  Level  Level} {γ : Level}
  (L : Large-Locale α β γ) (j : closure-operator-Large-Locale L)
  where

  large-subpreorder-closure-operator-Large-Locale :
    Large-Subpreorder α (large-preorder-Large-Locale L)
  large-subpreorder-closure-operator-Large-Locale {l1} x =
    Id-Prop (set-Large-Locale L l1) (map-closure-operator-Large-Locale L j x) x

  is-closed-element-closure-operator-Large-Locale :
    {l1 : Level}  type-Large-Locale L l1  UU (α l1)
  is-closed-element-closure-operator-Large-Locale =
    is-in-Large-Subpreorder
      ( large-preorder-Large-Locale L)
      ( large-subpreorder-closure-operator-Large-Locale)

  is-prop-is-closed-element-closure-operator-Large-Locale :
    {l1 : Level} (x : type-Large-Locale L l1) 
    is-prop (is-closed-element-closure-operator-Large-Locale x)
  is-prop-is-closed-element-closure-operator-Large-Locale =
    is-prop-is-in-Large-Subpreorder
      ( large-preorder-Large-Locale L)
      ( large-subpreorder-closure-operator-Large-Locale)

  is-closed-element-leq-closure-operator-Large-Locale :
    {l1 : Level} (x : type-Large-Locale L l1) 
    leq-Large-Locale L (map-closure-operator-Large-Locale L j x) x 
    is-closed-element-closure-operator-Large-Locale x
  is-closed-element-leq-closure-operator-Large-Locale x H =
    antisymmetric-leq-Large-Locale L
      ( map-closure-operator-Large-Locale L j x)
      ( x)
      ( H)
      ( is-inflationary-closure-operator-Large-Locale L j x)

  closed-element-closure-operator-Large-Locale :
    (l1 : Level)  UU (α l1)
  closed-element-closure-operator-Large-Locale =
    type-Large-Subpreorder
      ( large-preorder-Large-Locale L)
      ( large-subpreorder-closure-operator-Large-Locale)

  is-closed-under-sim-closure-operator-Large-Locale :
    {l1 l2 : Level}
    (x : type-Large-Locale L l1)
    (y : type-Large-Locale L l2) 
    leq-Large-Locale L x y  leq-Large-Locale L y x 
    is-closed-element-closure-operator-Large-Locale x 
    is-closed-element-closure-operator-Large-Locale y
  is-closed-under-sim-closure-operator-Large-Locale x y H K c =
    is-closed-element-leq-closure-operator-Large-Locale y
      ( transitive-leq-Large-Locale L
        ( map-closure-operator-Large-Locale L j y)
        ( map-closure-operator-Large-Locale L j x)
        ( y)
        ( transitive-leq-Large-Locale L
          ( map-closure-operator-Large-Locale L j x)
          ( x)
          ( y)
          ( H)
          ( leq-eq-Large-Locale L c))
        ( preserves-order-closure-operator-Large-Locale L j y x K))

  large-subposet-closure-operator-Large-Locale :
    Large-Subposet α (large-poset-Large-Locale L)
  large-subpreorder-Large-Subposet
    large-subposet-closure-operator-Large-Locale =
    large-subpreorder-closure-operator-Large-Locale
  is-closed-under-sim-Large-Subposet
    large-subposet-closure-operator-Large-Locale =
    is-closed-under-sim-closure-operator-Large-Locale

  large-poset-closure-operator-Large-Locale :
    Large-Poset α β
  large-poset-closure-operator-Large-Locale =
    large-poset-Large-Subposet
      ( large-poset-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale)

  leq-prop-closed-element-closure-operator-Large-Locale :
    Large-Relation-Prop α β closed-element-closure-operator-Large-Locale
  leq-prop-closed-element-closure-operator-Large-Locale =
    leq-prop-Large-Subposet
      ( large-poset-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale)

  leq-closed-element-closure-operator-Large-Locale :
    Large-Relation α β closed-element-closure-operator-Large-Locale
  leq-closed-element-closure-operator-Large-Locale =
    leq-Large-Subposet
      ( large-poset-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale)

  is-prop-leq-closed-element-closure-operator-Large-Locale :
    is-prop-Large-Relation
      ( closed-element-closure-operator-Large-Locale)
      ( leq-closed-element-closure-operator-Large-Locale)
  is-prop-leq-closed-element-closure-operator-Large-Locale =
    is-prop-leq-Large-Subposet
      ( large-poset-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale)

  refl-leq-closed-element-closure-operator-Large-Locale :
    is-reflexive-Large-Relation
      ( closed-element-closure-operator-Large-Locale)
      ( leq-closed-element-closure-operator-Large-Locale)
  refl-leq-closed-element-closure-operator-Large-Locale =
    refl-leq-Large-Subposet
      ( large-poset-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale)

  antisymmetric-leq-closed-element-closure-operator-Large-Locale :
    is-antisymmetric-Large-Relation
      ( closed-element-closure-operator-Large-Locale)
      ( leq-closed-element-closure-operator-Large-Locale)
  antisymmetric-leq-closed-element-closure-operator-Large-Locale =
    antisymmetric-leq-Large-Subposet
      ( large-poset-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale)

  transitive-leq-closed-element-closure-operator-Large-Locale :
    is-transitive-Large-Relation
      ( closed-element-closure-operator-Large-Locale)
      ( leq-closed-element-closure-operator-Large-Locale)
  transitive-leq-closed-element-closure-operator-Large-Locale =
    transitive-leq-Large-Subposet
      ( large-poset-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale)

  contains-top-large-subposet-closure-operator-Large-Locale :
    is-closed-element-closure-operator-Large-Locale
      ( top-Large-Locale L)
  contains-top-large-subposet-closure-operator-Large-Locale =
    antisymmetric-leq-Large-Locale L
      ( map-closure-operator-Large-Locale L j (top-Large-Locale L))
      ( top-Large-Locale L)
      ( is-top-element-top-Large-Locale L
        ( map-closure-operator-Large-Locale L j (top-Large-Locale L)))
      ( is-inflationary-closure-operator-Large-Locale L j (top-Large-Locale L))

  forward-implication-adjoint-relation-closure-operator-Large-Locale :
    {l1 l2 : Level}
    {x : type-Large-Locale L l1}
    {y : type-Large-Locale L l2} 
    is-closed-element-closure-operator-Large-Locale y 
    leq-Large-Locale L x y 
    leq-Large-Locale L (map-closure-operator-Large-Locale L j x) y
  forward-implication-adjoint-relation-closure-operator-Large-Locale
    {x = x} {y} H K =
    transitive-leq-Large-Locale L
      ( map-closure-operator-Large-Locale L j x)
      ( map-closure-operator-Large-Locale L j y)
      ( y)
      ( leq-eq-Large-Locale L H)
      ( preserves-order-closure-operator-Large-Locale L j
        ( x)
        ( y)
        ( K))

  backward-implication-adjoint-relation-closure-operator-Large-Locale :
    {l1 l2 : Level}
    {x : type-Large-Locale L l1}
    {y : type-Large-Locale L l2} 
    leq-Large-Locale L (map-closure-operator-Large-Locale L j x) y 
    leq-Large-Locale L x y
  backward-implication-adjoint-relation-closure-operator-Large-Locale
    {x = x} {y} H =
    transitive-leq-Large-Locale L
      ( x)
      ( map-closure-operator-Large-Locale L j x)
      ( y)
      ( H)
      ( is-inflationary-closure-operator-Large-Locale L j x)

  adjoint-relation-closure-operator-Large-Locale :
    {l1 l2 : Level}
    (x : type-Large-Locale L l1)
    (y : type-Large-Locale L l2) 
    is-closed-element-closure-operator-Large-Locale y 
    leq-Large-Locale L x y 
    leq-Large-Locale L (map-closure-operator-Large-Locale L j x) y
  pr1 (adjoint-relation-closure-operator-Large-Locale x y H) =
    forward-implication-adjoint-relation-closure-operator-Large-Locale H
  pr2 (adjoint-relation-closure-operator-Large-Locale x y H) =
    backward-implication-adjoint-relation-closure-operator-Large-Locale

  sup-closed-element-closure-operator-Large-Locale :
    {l1 l2 : Level} {I : UU l1}
    (x : I  closed-element-closure-operator-Large-Locale l2) 
    closed-element-closure-operator-Large-Locale (γ  l1  l2)
  pr1 (sup-closed-element-closure-operator-Large-Locale x) =
    map-closure-operator-Large-Locale L j (sup-Large-Locale L (pr1  x))
  pr2 (sup-closed-element-closure-operator-Large-Locale x) =
    is-idempotent-closure-operator-Large-Locale L j
      ( sup-Large-Locale L (pr1  x))

  is-least-upper-bound-sup-closed-element-closure-operator-Large-Locale :
    {l1 l2 : Level} {I : UU l1}
    (x : I  closed-element-closure-operator-Large-Locale l2) 
    is-least-upper-bound-family-of-elements-Large-Poset
      ( large-poset-closure-operator-Large-Locale)
      ( x)
      ( sup-closed-element-closure-operator-Large-Locale x)
  pr1
    ( is-least-upper-bound-sup-closed-element-closure-operator-Large-Locale x y)
    ( H) =
    forward-implication-adjoint-relation-closure-operator-Large-Locale
      ( pr2 y)
      ( forward-implication
        ( is-least-upper-bound-sup-Large-Locale L (pr1  x) (pr1 y))
        ( H))
  pr2
    ( is-least-upper-bound-sup-closed-element-closure-operator-Large-Locale x y)
    ( H) =
    backward-implication
      ( is-least-upper-bound-sup-Large-Locale L (pr1  x) (pr1 y))
      ( backward-implication-adjoint-relation-closure-operator-Large-Locale H)

  is-large-suplattice-large-poset-closure-operator-Large-Locale :
    is-large-suplattice-Large-Poset γ
      ( large-poset-closure-operator-Large-Locale)
  sup-has-least-upper-bound-family-of-elements-Large-Poset
    ( is-large-suplattice-large-poset-closure-operator-Large-Locale x) =
    sup-closed-element-closure-operator-Large-Locale x
  is-least-upper-bound-sup-has-least-upper-bound-family-of-elements-Large-Poset
    ( is-large-suplattice-large-poset-closure-operator-Large-Locale x) =
    is-least-upper-bound-sup-closed-element-closure-operator-Large-Locale x

  large-suplattice-closure-operator-Large-Locale :
    Large-Suplattice α β γ
  large-poset-Large-Suplattice
    large-suplattice-closure-operator-Large-Locale =
    large-poset-closure-operator-Large-Locale
  is-large-suplattice-Large-Suplattice
    large-suplattice-closure-operator-Large-Locale =
    is-large-suplattice-large-poset-closure-operator-Large-Locale

The predicate that the closed elements of a closure operator on a large locale are closed under meets

module _
  {α : Level  Level} {β : Level  Level  Level} {γ : Level}
  (L : Large-Locale α β γ) (j : closure-operator-Large-Locale L)
  where

  is-closed-under-meets-closure-operator-Large-Locale : UUω
  is-closed-under-meets-closure-operator-Large-Locale =
    is-closed-under-meets-Large-Subposet
      ( large-meet-semilattice-Large-Locale L)
      ( large-subposet-closure-operator-Large-Locale L j)

Properties

If the closed elements are closed under meets, then the closed elements of a closure operator form a large locale

We also assume that x ∧ j y = j (x ∧ y) for any closed element x. In large locales with exponentials it seems that we can omit this extra hypothesis.

module _
  {α : Level  Level} {β : Level  Level  Level} {γ : Level}
  (L : Large-Locale α β γ) (j : closure-operator-Large-Locale L)
  (H : is-closed-under-meets-closure-operator-Large-Locale L j)
  (K :
    {l1 l2 : Level} (x : type-Large-Locale L l1) (y : type-Large-Locale L l2) 
    is-closed-element-closure-operator-Large-Locale L j x 
    meet-Large-Locale L x (map-closure-operator-Large-Locale L j y) 
    map-closure-operator-Large-Locale L j (meet-Large-Locale L x y))
  where

  large-meet-subsemilattice-closure-operator-Large-Locale :
    Large-Meet-Subsemilattice α (large-meet-semilattice-Large-Locale L)
  large-subposet-Large-Meet-Subsemilattice
    large-meet-subsemilattice-closure-operator-Large-Locale =
    large-subposet-closure-operator-Large-Locale L j
  is-closed-under-meets-Large-Meet-Subsemilattice
    large-meet-subsemilattice-closure-operator-Large-Locale =
    H
  contains-top-Large-Meet-Subsemilattice
    large-meet-subsemilattice-closure-operator-Large-Locale =
    contains-top-large-subposet-closure-operator-Large-Locale L j

  large-meet-semilattice-closure-operator-Large-Locale :
    Large-Meet-Semilattice α β
  large-meet-semilattice-closure-operator-Large-Locale =
    large-meet-semilattice-Large-Meet-Subsemilattice
      ( large-meet-semilattice-Large-Locale L)
      ( large-meet-subsemilattice-closure-operator-Large-Locale)

  is-large-meet-semilattice-large-poset-closure-operator-Large-Locale :
    is-large-meet-semilattice-Large-Poset
      ( large-poset-closure-operator-Large-Locale L j)
  is-large-meet-semilattice-large-poset-closure-operator-Large-Locale =
    is-large-meet-semilattice-Large-Meet-Semilattice
      large-meet-semilattice-closure-operator-Large-Locale

  meet-closed-element-closure-operator-Large-Locale :
    {l1 l2 : Level} 
    closed-element-closure-operator-Large-Locale L j l1 
    closed-element-closure-operator-Large-Locale L j l2 
    closed-element-closure-operator-Large-Locale L j (l1  l2)
  meet-closed-element-closure-operator-Large-Locale =
    meet-Large-Meet-Semilattice
      large-meet-semilattice-closure-operator-Large-Locale

  distributive-meet-sup-closure-operator-Large-Locale :
    {l1 l2 l3 : Level}
    (x : closed-element-closure-operator-Large-Locale L j l1)
    {I : UU l2} (y : I  closed-element-closure-operator-Large-Locale L j l3) 
    meet-closed-element-closure-operator-Large-Locale x
      ( sup-closed-element-closure-operator-Large-Locale L j y) 
    sup-closed-element-closure-operator-Large-Locale L j
      ( λ i 
        meet-closed-element-closure-operator-Large-Locale x (y i))
  distributive-meet-sup-closure-operator-Large-Locale (x , p) y =
    eq-type-subtype
      ( large-subpreorder-closure-operator-Large-Locale L j)
      ( ( K x _ p) 
        ( ap
          ( map-closure-operator-Large-Locale L j)
          ( distributive-meet-sup-Large-Locale L x _)))

  large-frame-closure-operator-Large-Locale :
    Large-Frame α β γ
  large-poset-Large-Frame
    large-frame-closure-operator-Large-Locale =
    large-poset-closure-operator-Large-Locale L j
  is-large-meet-semilattice-Large-Frame
    large-frame-closure-operator-Large-Locale =
    is-large-meet-semilattice-large-poset-closure-operator-Large-Locale
  is-large-suplattice-Large-Frame
    large-frame-closure-operator-Large-Locale =
    is-large-suplattice-large-poset-closure-operator-Large-Locale L j
  distributive-meet-sup-Large-Frame
    large-frame-closure-operator-Large-Locale x y =
    distributive-meet-sup-closure-operator-Large-Locale x y

  large-locale-closure-operator-Large-Locale :
    Large-Locale α β γ
  large-locale-closure-operator-Large-Locale =
    large-frame-closure-operator-Large-Locale

Recent changes