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With the SAFT initial comma objects supplied for all spaces, they assemble into the compact-Hausdorff reflection and agree on Tychonoff spaces with the constructed Stone-Cech adjunction
Statement
Assume the ultrafilter lemma and dependent choice. For every topological space , objectwise SAFT gives an initial object of for the inclusion . If these initial objects are supplied for all , they assemble into a left adjoint .
After restricting the domain to Tychonoff spaces, is naturally isomorphic, as a left adjoint to the same inclusion, to the chosen Stone-Cech compactification functor .
Facts & Assumptions
Given: The ultrafilter lemma, dependent choice, and a supplied family of the objectwise initial comma objects.
Under these choice principles, the compact-Hausdorff inclusion satisfies the explicit supplied-well-powering SAFT hypotheses (Under the ultrafilter lemma and dependent choice, compact Hausdorff spaces satisfy the explicit SAFT hypotheses for their inclusion into topological spaces).
Objectwise SAFT gives initial comma objects, and a supplied family of them assembles into a left adjoint (Special adjoint functor theorem, objectwise form with explicit intersection smallness or preservation data, Special adjoint functor theorem, data-supplied functor form).
On Tychonoff spaces, the chosen Stone-Cech functor is left adjoint to the compact-Hausdorff inclusion (Under the ultrafilter lemma and dependent choice, Stone-Cech compactification is left adjoint to the compact-Hausdorff inclusion).
Two left adjoints to the same functor are naturally isomorphic by a unique natural isomorphism compatible with the adjunctions (Adjoints are unique up to a unique natural isomorphism compatible with the adjunction data).
Proof
For each topological space , [L1] and the objectwise part of [L2] give an initial object of .
Applying the functor form of [L2] to the supplied family assembles these universal arrows into .
Restrict and to Tychonoff spaces. By [L3], both and are left adjoint to the same compact-Hausdorff inclusion, so [L4] supplies the unique compatible natural isomorphism .
Depends on
- Under the ultrafilter lemma and dependent choice, compact Hausdorff spaces satisfy the explicit SAFT hypotheses for their inclusion into topological spaces
- Special adjoint functor theorem, objectwise form with explicit intersection smallness or preservation data
- Special adjoint functor theorem, data-supplied functor form
- Under the ultrafilter lemma and dependent choice, Stone-Cech compactification is left adjoint to the compact-Hausdorff inclusion
- Adjoints are unique up to a unique natural isomorphism compatible with the adjunction data
Used by
Dependency tree · next 3 levels
Direct dependencies and their dependencies through the next three levels: 99 results over 14 levels. An arrow runs from a result to what uses it, and this result sits at the bottom with a heavier outline. Click the chart to enlarge it.
Sources
- S. Mac Lane, Categories for the Working Mathematician, compact-Hausdorff example after V.8 (standard reference, not scraped)
- E. Riehl, Category Theory in Context, example 4.7.12 (standard reference, not scraped)