Giraud's theorem for Segal topoi
Giraud's theorem for Segal topoi
Let be a -small Segal category. A -Segal topos is a Segal category satisfying the conditions in the claim below; a coproduct is disjoint when its canonical squares with the initial object are cartesian, and a groupoid object is a simplicial object satisfying the Segal and invertibility conditions. For a groupoid object , write for the colimit of its simplicial diagram and for the nerve of the natural morphism.
Giraud's theorem for Segal topoi. is a -Segal topos if and only if:
- The simplicial sets of morphisms in are essentially -small.
- has all -small colimits, and coproducts in are disjoint.
- For every groupoid object in , the natural morphism
is an equivalence of simplicial objects in . 4. Colimits in are stable by pullbacks: for every -small category , every -diagram in , and morphisms from to and from to , the natural morphism
is an equivalence. 5. has a -small set of strong generators.
This is presented as the Segal-category analogue of Giraud's theorem, characterizing Segal topoi by smallness, colimits, disjoint coproducts, effective groupoid objects, pullback-stable colimits, and strong generators. The parser supplies no evidence that the claim has been resolved; its status is therefore open.
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Sources & referencesView supporting material
Primary source
Bertrand Toen and Gabriele Vezzosi, “Segal topoi and stacks over Segal categories”, arXiv:math/0212330 (2003).
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