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nLab > Latest Changes: (infinity,1)-Grothendieck construction

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    • CommentRowNumber1.
    • CommentAuthorHurkyl
    • CommentTimeMar 25th 2021

    I added a short abstract description of the Cartesian fibration over the interval, and commented that the section describes a construction with additional strictness properties in the quasi-category model.

    diff, v43, current

    • CommentRowNumber2.
    • CommentAuthorHurkyl
    • CommentTimeApr 1st 2021
    • (edited Apr 1st 2021)

    In the statement for general fibered categories, the way it was stated seemed to be assuming that CC was small, so I made the assumption explicit. I also clarified the arrows of Cart(C)Cart(C) are just the cartesian functors.

    I also added the statement that the construction gives a natural equivalence.

    Random aside: the language I’ve seen clarifying which functor is meant by just saying its action on morphisms – e.g. that Cart(−)Cart(-) acts on morphisms by pullback – is dissatisfying, but I don’t really know a better way to state that without being overly cumbersome. Is there a better way of phrasing it?

    diff, v44, current

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeOct 9th 2021

    I have adjusted the first sentences of the Idea-section, which were essentially unreadable with their nested case distinctions.

    Also I moved the proposition about the case of ∞\infty-groupoids over ∞\infty-groupoids up to (here) right after the statement of the (∞,0)(\infty,0)-Grothendieck construction (for it uses nothing else that would be discussed later and usefully completes the picture at this point)

    It’s this Prop. that is used over at shape of an (infinity,1)-topos and I will finally link to it from there.

    diff, v45, current

    • CommentRowNumber4.
    • CommentAuthorHurkyl
    • CommentTimeNov 10th 2021

    Corrected the typo that \natural was converted to \sharp when copying over an argument from HTT 5.2.1.3.

    diff, v46, current

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeDec 28th 2021

    Here is a question:

    Given an ∞\infty-presheaf 𝒳:𝒞 op→Grpd ∞\mathcal{X} \,\colon\, \mathcal{C}^{op} \xrightarrow{\;} Grpd_\infty, its ∞\infty-Grothendieck construction is naturally fibered over that of its nn-truncation (for any n∈ℕn \in \mathbb{N}):

    ∫c∈𝒞𝒳(c) ↓ P n ∫c∈𝒞τ n𝒳(c) \array{ \overset{c \in \mathcal{C}}{\int} \mathcal{X}(c) \\ \big\downarrow {}^{\mathrlap{P_n}} \\ \overset{c \in \mathcal{C}}{\int} \tau_n\mathcal{X}(c) }

    This map itself is the ∞\infty-Grothendieck construction of some ∞\infty-functor

    ∫c∈𝒞τ n𝒳(c)→Grpd ∞. \overset{c \in \mathcal{C}}{\int} \tau_n\mathcal{X}(c) \; \xrightarrow{\;\;\;\;\;\;\;} \; Grpd_\infty \,.

    What is this ∞\infty-functor? I suppose it should the the functor that assigns the system of nn-connected covers of 𝒳\mathcal{X}:

    (c,x)↦cn n(𝒳(c),x). (c,x) \;\mapsto\; cn_n\big( \mathcal{X}(c), x \big) \,.

    Is this right? Is this discussed/proven anywhere?

    I have put a note with some elaboration on this question into the Sandbox (using some tikz-typesetting, which doesn’t display here on the nnForum).

    • CommentRowNumber6.
    • CommentAuthorUrs
    • CommentTimeDec 29th 2021

    While the nnLab is migrating, I made a pdf-note

    with the answer to my question in #5.

    (But it’s still missing an argument that ∫𝒳→∫τ n𝒳\int \mathcal{X} \xrightarrow{\;} \int \tau_n \mathcal{X} is itself a left fibration in the first place.)

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeJul 7th 2022
    • (edited Jul 7th 2022)

    added pointer to

    for disucssion of the ∞\infty-Grothendieck construction for ∞\infty-functors to ∞\infty-toposes from inverse images of ∞\infty-groupoids.

    diff, v49, current

    • CommentRowNumber8.
    • CommentAuthorTim_Porter
    • CommentTimeSep 27th 2022

    Fixed grammatical typo.

    diff, v51, current

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeOct 19th 2022

    added pointer to today’s

    diff, v52, current

1 to 9 of 9

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