Abstract
We introduce, comment and develop the Scott adjunction, mostly from the point of view of a category theorist. Besides its technical and conceptual aspects, in a nutshell we provide a categorification of the Scott topology over a posets with directed suprema. From a technical point of view we establish an adjunction between accessible categories with directed colimits and Grothendieck topoi. We show that the bicategory of topoi is enriched over the 2-category of accessible categories with directed colimits and it has tensors with respect to this enrichment. The Scott adjunction (re-)emerges naturally from this observation.
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Notes
This is shown in Remark 2.7.
This will be shown in the remark below.
The free completions that adds splittings of pseudo-idempotents.
These are those limits can be reduced to products, inserters and equifiers.
i.e., send filtered colimits in \(\mathscr {A}\) or \(\mathscr {B}\) to limits in \(\mathbf{Set}\).
Here we are using that \(\mathscr {A}\) and \(\mathscr {B}\) are accessible in order to cut down the size of the orthogonality.
This is not strictly true, because the definition of monoidal closed category does not allow for equivalence of categories. We did not find a precise terminology in the literature and we felt non-useful to introduce a new concept for such a small discrepancy.
This is not quite true, we know that e is a subquotient of \(f^*(g)\), in the general case the proof gets a bit messier to follow, for this reason we will cover in detail just this case.
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Acknowledgements
I am indebted to my advisor, Jiří Rosický, for the freedom and the trust he blessed me with during these years, not to mention his sharp and remarkably blunt wisdom. I would like to thank Simon Henry, for his collaboration in those days in which this project was nothing but an informal conversation at the whiteboard. I am grateful to Peter Arndt, for his sincere interest in my research, and the hint of looking at the example of the geometric theory of fields. Finally, I am grateful to the anonymous referee for their suggestions and comments.
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This research was mostly developed during the Ph.D. studies of the author and has been supported through the Grant 19-00902S from the Grant Agency of the Czech Republic. The finalization of this research has been supported by the GACR Project EXPRO 20-31529X and RVO: 67985840.
Communicated by Thomas Streicher.
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Di Liberti, I. General Facts on the Scott Adjunction. Appl Categor Struct 30, 569–591 (2022). https://doi.org/10.1007/s10485-021-09666-6
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DOI: https://doi.org/10.1007/s10485-021-09666-6