Constructions of diffeological spaces #
This file gives some concrete constructions like products and coproducts of
diffeological spaces. General limits and colimits are found in
Orbifolds.Diffeology.DiffSp
.
Mostly based on Mathlib.Topology.Constructions
.
TODO #
- binary disjoint unions
- arbitrary disjoint unions
- more API on arbitrary products
Equations
Equations
- Pi.diffeologicalSpace = ⨅ (i : ι), DiffeologicalSpace.induced (fun (x : (i : ι) → Y i) => x i) (D i)
Additive
, Multiplicative
#
The diffeology on those type synonyms is inherited without change.
Equations
Equations
Order dual #
The diffeology on this type synonym is inherited without change.
Equations
On an open subset, a function is smooth in the usual sense iff it is smooth diffeologically.
On open subsets, the D-topology and subspace topology agree.
Smoothness can also be characterised as preserving smooth maps u → X
for open u
.
Any D-locally constant map is smooth.
The indiscrete diffeology is the one for which every map is a plot.
The discrete diffeologoy is the only diffeology whose D-topology is discrete. Note that the corresponding statement for indiscrete spaces is false.
A map from an indiscrete space is smooth iff its range is indiscrete. Note that this can't be characterised purely topologically, since it might be the case that all involved D-topologies are indiscrete but the diffeologies are not.
A map to an discrete space is smooth iff it is D-locally constant.
A map is a plot in the coinduced diffeology iff it is constant or lifts locally.
For surjective functions, the plots of the coinduced diffeology are precicely those that locally lift.
The D-topology is coinduced by all plots.
The topology coinduced by a map out of a sigma type is the surpremum of the topologies
coinduced by its components.
Maybe should go into mathlib? A similar induced_to_pi
is already there.
The D-topology is coinduced by the sum of all plots.
The D-topology is always delta-generated.
Diffeological spaces are always delta-generated when equipped with the D-topology.
The plots of the quotient diffeology are precicely those that locally lift to plots.
The plots of the quotient diffeology are precicely those that locally lift to plots.
A version of dsmooth_inf_dom_left
for binary functions
A version of dsmooth_inf_dom_right
for binary functions
A version of dsmooth_sInf_dom
for binary functions
Smooth functions on products are smooth in their first argument
Alias of DSmooth.curry_left
.
Smooth functions on products are smooth in their first argument
Smooth functions on products are smooth in their second argument
Alias of DSmooth.curry_right
.
Smooth functions on products are smooth in their second argument
The first projection in a product of diffeological spaces is a subduction.
The second projection in a product of diffeological spaces is a subduction.
A product of induced diffeologies is induced by the product map.
The diffeology coinduced by a product map is at least as fine as the product of the coinduced diffelogies. Note that equality only holds when both maps are surjective.
A product of coinduced diffeologies is coinduced by the product map, if both maps are surjective.
Products of reflexive diffeological spaces are reflexive.
Products of normed spaces are compatible with the product diffeology.
The D-topology of the product diffeology is at least as fine as the product of the D-topologies.
For locally compact spaces X
, the product functor X × -
takes quotient maps to quotient
maps. Note that surjectivity is actually required here - coinducing maps do not necessarily
get taken to coinducing maps.
Adapted from
https://dantopology.wordpress.com/2023/04/21/the-product-of-the-identity-map-and-a-quotient-map/.
TODO: give an explicit description of the coinduced topology without assuming surjectivity
TODO: give an explicit description even without local compactness, using deltaGenerated
TODO: maybe move to mathlib?
Analogous to QuotientMap.id_prod
.
Equivalent of Function.Surjective.sigma_map
for quotient maps.
TODO: move to mathlib.
For locally compact diffeological spaces, the D-topology commutes with products. This is not true in general, because the product topology might not be delta-generated; however, according to a remark in https://arxiv.org/abs/1302.2935 it should be always true if one takes the product in the category of delta-generated spaces instead of in Top. TODO: work this all out more generally
Version of dTop_prod_eq_prod_dTop_of_locallyCompact_left
where the second factor
is assumed to be locally compact instead of the first one.
The functional diffeology on the space DSmoothMap X Y
of smooth maps X → Y
.
Equations
- One or more equations did not get rendered due to their size.
A map f : X → DSmoothMap Y Z
is smooth iff the corresponding map X × Y → Z
is.
The evaluation map DSmoothMap X Y × X → Y
is smooth.
The composition map DSmoothMap Y Z × DSmoothMap X Y → DSmoothMap X Z
is smooth.
The coevaluation map Y → DSmoothMap X (Y × X)
.
Equations
- DSmoothMap.coev y = { toFun := fun (x : X) => (y, x), dsmooth := ⋯ }
Instances For
The coevaluation map is smooth.
The currying map DSmoothMap (X × Y) Z → DSmoothMap X (DSmoothMap Y Z)
Equations
- f.curry = { toFun := fun (x : X) => { toFun := Function.curry (⇑f) x, dsmooth := ⋯ }, dsmooth := ⋯ }
Instances For
The currying map is smooth.
The uncurrying map DSmoothMap X (DSmoothMap Y Z) → DSmoothMap (X × Y) Z
.
Instances For
The uncurrying map is smooth.
The projection X × Y → X
as a DSmoothMap
.
Equations
- DSmoothMap.fst = { toFun := Prod.fst, dsmooth := ⋯ }
Instances For
The projection X × Y → Y
as a DSmoothMap
.
Equations
- DSmoothMap.snd = { toFun := Prod.snd, dsmooth := ⋯ }
Instances For
The continuous map X → Y × Z
corresponding to two maps X → Y
, X → Z
.
Instances For
The equivalence between smooth functions X → Y
and plain functions when X
is discrete.
TODO: replace the topological assumptions with [DiscreteDiffeology X]
once that is defined.
Equations
- DSmoothMap.equivFnOfDiscrete = { toFun := fun (f : DSmoothMap X Y) => ⇑f, invFun := fun (f : X → Y) => { toFun := f, dsmooth := ⋯ }, left_inv := ⋯, right_inv := ⋯ }
Instances For
The equivalence between smooth functions X → Y
and Y
when X
is discrete.
TODO: remove topological assumptions.
TODO: DDiffeomorph
variants of these two constructions.