Inseparable points in a topological space #
In this file we prove basic properties of the following notions defined elsewhere.
Specializes
(notation:x ⤳ y
) : a relation saying that𝓝 x ≤ 𝓝 y
;Inseparable
: a relation saying that two points in a topological space have the same neighbourhoods; equivalently, they can't be separated by an open set;InseparableSetoid X
: same relation, as aSetoid
;SeparationQuotient X
: the quotient ofX
by itsInseparableSetoid
.
We also prove various basic properties of the relation Inseparable
.
Notations #
x ⤳ y
: notation forSpecializes x y
;x ~ᵢ y
is used as a local notation forInseparable x y
;𝓝 x
is the neighbourhoods filternhds x
of a pointx
, defined elsewhere.
Tags #
topological space, separation setoid
Specializes
relation #
A collection of equivalent definitions of x ⤳ y
. The public API is given by iff
lemmas
below.
Alias of the forward direction of specializes_iff_nhds
.
Alias of the forward direction of specializes_iff_pure
.
Alias of the forward direction of specializes_iff_mem_closure
.
Alias of the forward direction of specializes_iff_closure_subset
.
Alias of specializes_of_eq
.
Alias of IsInducing.specializes_iff
.
A continuous function is monotone with respect to the specialization preorders on the domain and the codomain.
A subset S
of a topological space is stable under specialization
if x ∈ S → y ∈ S
for all x ⤳ y
.
Equations
- StableUnderSpecialization s = ∀ ⦃x y : X⦄, x ⤳ y → x ∈ s → y ∈ s
Instances For
A subset S
of a topological space is stable under specialization
if x ∈ S → y ∈ S
for all y ⤳ x
.
Equations
- StableUnderGeneralization s = ∀ ⦃x y : X⦄, y ⤳ x → x ∈ s → y ∈ s
Instances For
Alias of the reverse direction of stableUnderSpecialization_compl_iff
.
Alias of the reverse direction of stableUnderGeneralization_compl_iff
.
Alias of the forward direction of stableUnderSpecialization_iff_Union_eq
.
A set is stable under specialization iff it is a union of closed sets.
A set is stable under generalization iff it is an intersection of open sets.
A map f
between topological spaces is specializing if specializations lifts along f
,
i.e. for each f x' ⤳ y
there is some x
with x' ⤳ x
whose image is y
.
Equations
- SpecializingMap f = Relation.Fibration (flip fun (x1 x2 : X) => x1 ⤳ x2) (flip fun (x1 x2 : Y) => x1 ⤳ x2) f
Instances For
A map f
between topological spaces is generalizing if generalizations lifts along f
,
i.e. for each y ⤳ f x'
there is some x ⤳ x'
whose image is y
.
Equations
- GeneralizingMap f = Relation.Fibration (fun (x1 x2 : X) => x1 ⤳ x2) (fun (x1 x2 : Y) => x1 ⤳ x2) f
Instances For
Alias of the forward direction of specializingMap_iff_closure_singleton_subset
.
Alias of IsInducing.specializingMap
.
Alias of IsInducing.generalizingMap
.
Alias of IsOpenEmbedding.generalizingMap
.
Inseparable
relation #
Alias of IsInducing.inseparable_iff
.
Separation quotient #
In this section we define the quotient of a topological space by the Inseparable
relation.
Equations
- instTopologicalSpaceSeparationQuotient X = instTopologicalSpaceQuotient
The natural map from a topological space to its separation quotient.
Equations
- SeparationQuotient.mk = Quotient.mk''
Instances For
Alias of SeparationQuotient.isQuotientMap_mk
.
Equations
- ⋯ = ⋯
Equations
- SeparationQuotient.instInhabited = { default := SeparationQuotient.mk default }
Equations
- ⋯ = ⋯
Equations
- SeparationQuotient.instZero = { zero := SeparationQuotient.mk 0 }
Equations
- SeparationQuotient.instOne = { one := SeparationQuotient.mk 1 }
Alias of SeparationQuotient.isInducing_mk
.
The map (x, y) ↦ (mk x, mk y)
is a quotient map.
Alias of SeparationQuotient.isQuotientMap_prodMap_mk
.
The map (x, y) ↦ (mk x, mk y)
is a quotient map.
Lift a map f : X → α
such that Inseparable x y → f x = f y
to a map
SeparationQuotient X → α
.
Equations
- SeparationQuotient.lift f hf x = Quotient.liftOn' x f hf
Instances For
Lift a map f : X → Y → α
such that Inseparable a b → Inseparable c d → f a c = f b d
to a
map SeparationQuotient X → SeparationQuotient Y → α
.
Equations
- SeparationQuotient.lift₂ f hf x y = Quotient.liftOn₂' x y f hf