Not signed in (Sign In)

Start a new discussion

Not signed in

Want to take part in these discussions? Sign in if you have an account, or apply for one below

  • Sign in using OpenID

Site Tag Cloud

2-category 2-category-theory abelian-categories adjoint algebra algebraic algebraic-geometry algebraic-topology analysis analytic-geometry arithmetic arithmetic-geometry book bundles calculus categorical categories category category-theory chern-weil-theory cohesion cohesive-homotopy-type-theory cohomology colimits combinatorics complex complex-geometry computable-mathematics computer-science constructive cosmology deformation-theory descent diagrams differential differential-cohomology differential-equations differential-geometry digraphs duality elliptic-cohomology enriched fibration foundation foundations functional-analysis functor galois-theory gauge-theory gebra geometric-quantization geometry graph graphs gravity grothendieck group group-theory harmonic-analysis higher higher-algebra higher-category-theory higher-differential-geometry higher-geometry higher-lie-theory higher-topos-theory homological homological-algebra homotopy homotopy-theory homotopy-type-theory index-theory integration integration-theory k-theory lie-theory limits linear linear-algebra locale localization logic manifolds mathematics measure-theory modal modal-logic model model-category-theory monad monads monoidal monoidal-category-theory morphism motives motivic-cohomology nlab noncommutative noncommutative-geometry number number-theory of operads operator operator-algebra order-theory pages pasting philosophy physics pro-object probability probability-theory quantization quantum quantum-field quantum-field-theory quantum-mechanics quantum-physics quantum-theory question representation representation-theory riemannian-geometry scheme schemes set set-theory sheaf simplicial space spin-geometry stable-homotopy-theory string string-theory subobject superalgebra supergeometry svg symplectic-geometry synthetic-differential-geometry terminology theory topology topos topos-theory type type-theory universal variational-calculus

Vanilla 1.1.10 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to nForum
If you want to take part in these discussions either sign in now (if you have an account), apply for one now (if you don't).
    • CommentRowNumber1.
    • CommentAuthorHurkyl
    • CommentTimeMar 8th 2021

    Added direct descriptions of the various universal fibrations.

    diff, v12, current

    • CommentRowNumber2.
    • CommentAuthorHurkyl
    • CommentTimeMar 9th 2021

    Figured the proof of the description for the universal (co)cartesian fibration would be better duplicated here

    diff, v13, current

    • CommentRowNumber3.
    • CommentAuthorHurkyl
    • CommentTimeMar 14th 2021

    Described the hom-spaces in the universal cocartesian fibration, and that it can be constructed using a lax coslice.

    diff, v14, current

    • CommentRowNumber4.
    • CommentAuthorUrs
    • CommentTimeMar 14th 2021
    • (edited Mar 14th 2021)

    tried to give the references to online resources more canonical and more informative formatting: how about doing pointers to Kerdodon like this (with an eye towards their own request here on how to cite them):

    diff, v15, current

    • CommentRowNumber5.
    • CommentAuthorHurkyl
    • CommentTimeMar 24th 2021

    I think there isn’t a consistent naming scheme whether the universal cocartesian fibration uses lax points or oplax points, so I’ve remarked on that ambiguity.

    diff, v16, current

    • CommentRowNumber6.
    • CommentAuthorUrs
    • CommentTimeDec 29th 2021

    added pointer to:

    diff, v17, current

    • CommentRowNumber7.
    • CommentAuthorHurkyl
    • CommentTimeMar 28th 2022
    • (edited Mar 28th 2022)

    Here’s a subtle issue in my construction of the universal cocartesian fibration that I’m wondering if there is an easy solution to.

    Consider two functors CatCat^\infty Cat \to \widehat{\infty Cat} from small \infty-categories to large \infty-categories given as follows:

    • The covariant functor P()P(-), the “\infty-category of presheaves”, where functorality comes from the universal property Fun L(P(C),E)Fun(C,E)Fun^L(P(C), E) \simeq Fun(C, E) for \infty-categories EE with small colimits.
    • The contravariant functor R=Fun(() op,Gpd)R = Fun((-)^{op}, \infty Gpd)

    Lurie defines PP pointwise by setting P(C)=Fun(C op,Gpd)P(C) = Fun(C^{op}, \infty Gpd), so the content of the first bullet point is to make it into a functor.

    These two functors are closely related; for any functor f:CDf : C \to D, Proposition of Higher Topos Theory proves that P(f)R(f)P(f) \dashv R(f).

    Let el¯(R)Cat\overline{el}(R) \to \infty Cat be the cartesian fibration classified by RR. This is a presentable fibration, so it is also a cocartesian fibration that is classified by a covariant functor R ladjR^{ladj}.

    It’s clear PP and R ladjR^{ladj} agree strictly objects and up to equivalence on arrows… but I realize now I have a gap in that I don’t actually know there is a natural equivalence between them. Is there any easy or general method for arriving at that conclusion from that sort of method? Or does closing this gap rely more on diving into the specifics of how PP is defined?

    • CommentRowNumber8.
    • CommentAuthorHurkyl
    • CommentTimeMar 30th 2022
    • (edited Mar 30th 2022)

    Here’s a concrete conjecture.

    Let F:C opCatF : C^{op} \to \infty\!Cat and G:CCatG : C \to \infty\!Cat. Suppose:

    • For each object cc in CC, we have F(c)=G(c)F(c) = G(c) (probably better to just require an equivalence)
    • For each arrow f:cdf : c \to d in CC, an adjunction G(f)F(f)G(f) \dashv F(f)

    I conjecture that this data can be extended to a natural equivalence GF ladjG \simeq F^{ladj}, where F ladjF^\ladj is the functor constructed from FF by reversing the action on arrows via taking left adjoints. To be more precise, I claim this data can be used to produce a bundle p:XCp : X \to C such that pp is both a cocartesian fibration classified by GG and a cartesian fibration classified by FF. I probably want to include some consistency constraint with the specified adjunctions as well.

    The reason that there is hope that it is enough to observe the relationship between how FF and GG act on arrows is that uniqueness of adjoints might be able to fill in the rest of the missing data. This seems like a mess to actually work through, though.

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeJun 24th 2022

    Where the universal left fibration was mentioned (here), I have added pointer also to

    diff, v18, current

Add your comments
  • Please log in or leave your comment as a "guest post". If commenting as a "guest", please include your name in the message as a courtesy. Note: only certain categories allow guest posts.
  • To produce a hyperlink to an nLab entry, simply put double square brackets around its name, e.g. [[category]]. To use (La)TeX mathematics in your post, make sure Markdown+Itex is selected below and put your mathematics between dollar signs as usual. Only a subset of the usual TeX math commands are accepted: see here for a list.

  • (Help)