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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeMay 18th 2011
    • (edited Oct 23rd 2012)

    I have expanded Lawvere-Tierney topology, also reorganized it in the process

    • CommentRowNumber2.
    • CommentAuthorzskoda
    • CommentTimeMay 18th 2011

    In

    • C. Cassidy, M. Hébert, G. M. Kelly, Reflective subcategories, localizations and factorization systems, J. Austral. Math. Soc. Ser. A 38 (1985), no. 3, 287–329, MR86j:18001; Corrigenda: “Reflective subcategories, localizations and factorization systems”, J. Austral. Math. Soc. Ser. A 41 (1986), no. 2, 286, MR87f:18001

    there is somewhat strange wording “Grothendieck-Lawvere-Tierney topologies”. He cites also some related articles to the topic of connection between topologies and localization, including a work of Borceux, which I can not find online (the MathReviews entry is quite useful though). Is there somebody who has the access ?

    • Francis Borceux, Sheaves of algebras for a commutative theory, Ann. Soc. Sci. Bruxelles Sér. I 95 (1981), no. 1, 3–19, MR83c:18006
    • CommentRowNumber3.
    • CommentAuthorzskoda
    • CommentTimeMay 18th 2011
    • (edited May 18th 2011)

    By localization C. Cassidy, M. Hébert, G. M. Kelly mean a more narrow sense of exact localization functor having right adjoint (i.e. a left exact reflection, they say “reflexion”). They say in the introduction

    Localizations have been extensively studied for certain classes of categories AA. When AA is the presheaf category [K,Set]][K,Set]] they correspond to the Grothendieck topologies on KK; and more generally when AA is any topos, they correspond to Grothendieck-Lawvere-Tierney topologies on AA; see [9]. When AA is an additive functor category [K,Ab][K,Ab], such as a category of modules, they correspond to Gabriel topologies, which are an additive analogue of the Grothendieck ones; see [13] and [14]. This has been further generalized by Borceux [3], replacing SetSet and AbAb by the symmetric monoidal category of algebras fo any commutative Lawvere theory.

    Borceux [3] is the one quoted in reply 2 of this thread. The last two paragraphs of the MathReviews record MR83c:18006 for Borceux [3] (written by Harvey Wolf) says

    To get a more tractable theory, the author restricts to the case where T\mathbf{T} is a commutative theory, in which case Set T\text{Set}^{\mathbf{T}} is a closed category. In this context, he considers a small Set T\text{Set}^{\mathbf {T}}-category 𝒞\mathcal{C} and the Set T\text{Set}^{\mathbf{T}}-category [𝒞 op,Set T][\mathcal{C}^{\text{op}},\text{Set}^{\mathbf{T}}]. He defines a T\mathbf{T}-sieve as a subfunctor of 𝒞(,x):𝒞 opSet T\mathcal{C}(-,x)\colon\mathcal{C}^{\text{op}}\rightarrow\text{Set}^{\mathbf{T}}. A T\mathbf{T}-topology is a set J(x)J(x) of T\mathbf{T}-sieves for every xx, satisfying the usual properties. He discusses the notion of a sheaf relative to such a topology and proves the existence and exactness of the associated sheaf functor.

    The author shows, in the context of a commutative theory, that there is an object Ω T\Omega_{\mathbf{T}} in [𝒞 op,Set][\mathcal{C}^{\text{op}},\text{Set}] which classifies subobjects in [𝒞 op,Set T][\mathcal{C}^{\text{op}},\text{Set}^{\mathbf{T}}] and such that there exist bijections between the following:

    (1) localizations of [𝒞 op,Set T][\mathcal{C}^{\text{op}},\text{Set}^{\mathbf{T}}];

    (2) T\mathbf{T}-topologies on 𝒞\mathcal{C}; and

    (3) morphisms j:Ω TΩ Tj\colon\Omega_{\mathbf{T}}\rightarrow\Omega_{\mathbf{T}} satisfying the Lawvere-Tierney axioms for a topology.

    In the final section of the paper it is shown that for each localization 𝒜 j\mathcal{A}_j of [𝒞 op,Set T][\mathcal{C}^{\text{op}},\text{Set}^{\mathbf{T}}] there exists an object Ω j\Omega_j in [𝒞 op,Set][\mathcal{C}^{\text{op}},\text{Set}] which plays a role analogous to that played by Ω T\Omega_{\mathbf{T}} for [𝒞 op,Set T][\mathcal{C}^{\text{op}},\text{Set}^{\mathbf{T}}].

    • CommentRowNumber4.
    • CommentAuthorzskoda
    • CommentTimeMay 18th 2011
    • (edited May 18th 2011)

    I find very beautiful the generalization from the review quoted in (3). It is enriched version of Lawvere-Tierney topology, for a limited class of enrichments (over Set TSet^{\mathbf{T}}, for a commutative theory T\mathbf{T} in SetSet). However, I do not have the access to the original paper. I added a paragraph into Lawvere-Tierney topology.

    I have to also understand the connection to Gabriel localization. The latter was the original motivation of Rosenberg to introduce Q-categories, and at some point he told me that the idea is related to the idea of Lawvere-Tierney in non-topos setup. I am sure he is not aware of the article by Borceux though.

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeMay 18th 2011

    Thanks, Zoran, interesting.

    I tried to find that article by Borceux that you mention, but can’t find it either. I can see a followup “Algebraic localization” but that’s a Springer LNM volume and Springer is asking me to pay for it (I never quite understand why we are apparently not subscribed to such volumes online).

    • CommentRowNumber6.
    • CommentAuthorzskoda
    • CommentTimeMay 18th 2011
    • (edited May 18th 2011)

    I would like that original paper, it seems more interesting for my purposes, than the other papers of Borceux from about the same time. I can get the LNM volume, though, and I have the

    • Francis Borceux, Gilberte Van Den Bossche, Recovering a frame from its sheaves of algebras, Journal of Pure and Applied Algebra 28, 2, May 1983, 141-154, doi

    P.S. The paper in the LNM Gummersbach volume has only short sketches of proofs. Supposedly there is a larger French preprint version with full proofs.

    • Francis Borceux, Sur les localisations algébriques, Preprint, Rapp. Sém. Math. Pures, Univ. Louvain, Louvain, Belgium, 1981
    • CommentRowNumber7.
    • CommentAuthorzskoda
    • CommentTimeMay 18th 2011
    • (edited May 18th 2011)

    Oh, Urs, maybe you were not talking the short article in Gummersbach LNM volume (what I assumed)

    • Francis Borceux, On algebraic localizations, MR84c:18007, in Category theory (Gummersbach, 1981), pp. 13–22, Lecture Notes in Math. 962, Springer 1982.

    but the later LNM volume

    • Francis Borceux, Gilberte Van den Bossche, Algebra in a localic topos with applications to ring theory, Lecture Notes in Mathematics 1038, Springer-Verlag, Berlin, 1983. ix+240 pp. MR85h:18005

    I can get that one too. I added the above bibliographic entries to Francis Borceux.

    • CommentRowNumber8.
    • CommentAuthorzskoda
    • CommentTimeMay 18th 2011

    Borceux-Bossche say that the correspondence between left exact localizations and Gabriel-Grothendieck topologies (that is an enriched version of Grothendieck topologies) fails once one gets to non-commutative theories. This was I think precisely the motivation for the introduction of sheaves on Q-categories rather than on Gabriel-Grothendieck sites in noncommutative algebraic geometry.

    • CommentRowNumber9.
    • CommentAuthorzskoda
    • CommentTimeMay 18th 2011
    • (edited May 18th 2011)

    Enrico Vitale was kind to send me the pdf scan of Borceux’s article from item 2 (Sheaves of algebras for a commutative theory).

    • CommentRowNumber10.
    • CommentAuthorDavidRoberts
    • CommentTimeMay 18th 2011

    @Zoran #3 - I think ’reflexion’ would be Max Kelly. I was in a talk once where he interjected about the distinction between ’dilation’ and ’dilatation’, quoting the Latin derivation to prove his point. :)

    • CommentRowNumber11.
    • CommentAuthorFinnLawler
    • CommentTimeMay 19th 2011

    Zoran: re enriched Grothendieck topologies, have you seen Borceux and Quinteiro, A theory of enriched sheaves, Cahiers 37(2), 1996?

    • CommentRowNumber12.
    • CommentAuthorzskoda
    • CommentTimeMay 19th 2011
    • (edited May 19th 2011)

    No, I have not. Thanks.

    It is a bit dissappointing that those works with theories need commutative theories, what makes it strange that they mention Gabriel when they say Gabriel-Grothendieck topologies, as Gabriel’s work on abelian localization is mainly made for (categories of modules over) noncommutative rings.

    So let me see the paper you suggest. Here is the full record now

    • Francis Borceux, Carmen Quinteiro, A theory of enriched sheaves, Cahiers de Topologie et Géométrie Différentielle Catégoriques 37 no. 2 (1996), p. 145-162, numdam

    They enrich over symmetric monoidal category.

    • CommentRowNumber13.
    • CommentAuthorUrs
    • CommentTimeDec 5th 2011
    • (edited Dec 5th 2011)

    I am adding to Lawvere-Tierney topology a subsection Properties – Relation to lex reflectors. This is supposed to expose the baby-version of the \sharp-escape theory that Mike recently developed on the Café

    • CommentRowNumber14.
    • CommentAuthorMike Shulman
    • CommentTimeDec 6th 2011

    Nice, thanks!

    • CommentRowNumber15.
    • CommentAuthorUrs
    • CommentTimeOct 23rd 2012

    Added to Lawvere-Tierney operator links to geometric modality (currently redirecting to modal type theory) and added a pointer to Goldblatt’s article to the References-section.

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