* sieves in nLab @ 2011-03-01 19:18 Vasili I. Galchin 2011-03-02 20:04 ` Toby Bartels [not found] ` <20110302200410.GA17666@ugcs.caltech.edu> 0 siblings, 2 replies; 3+ messages in thread From: Vasili I. Galchin @ 2011-03-01 19:18 UTC (permalink / raw) To: Categories mailing list Hello, I am confused about the notion of "encoding" regarding sieves: ." And sieves on objects are mostly used in the context of Grothendieck topologies to encode presheaves that behave like coverings" "Sieves are an equivalent way to encode subobjects of representable functors in a presheaf category in terms of the total sets of elements of such a subfunctor." "It is in this way that sieves and their associated subfunctors encode the notion of cover of an object V: they tell us which of all the maps into V do factor through the cover." Regards, Vasili [For admin and other information see: http://www.mta.ca/~cat-dist/ ] ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: sieves in nLab 2011-03-01 19:18 sieves in nLab Vasili I. Galchin @ 2011-03-02 20:04 ` Toby Bartels [not found] ` <20110302200410.GA17666@ugcs.caltech.edu> 1 sibling, 0 replies; 3+ messages in thread From: Toby Bartels @ 2011-03-02 20:04 UTC (permalink / raw) To: Categories mailing list; +Cc: Urs Schreiber Vasili I. Galchin wrote in part on the categories list: >I am confused about the notion of "encoding" regarding sieves: Looking through the history of the page, it seems that Urs Schreiber introduced that term. So he might be able to say what he meant by it. (I'm pretty sure that he reads this list, but I'll Cc him to be safe.) By the way, the page is http://ncatlab.org/nlab/show/sieve for anybody who doesn't know how to find it. --Toby [For admin and other information see: http://www.mta.ca/~cat-dist/ ] ^ permalink raw reply [flat|nested] 3+ messages in thread
[parent not found: <20110302200410.GA17666@ugcs.caltech.edu>]
* Re: sieves in nLab [not found] ` <20110302200410.GA17666@ugcs.caltech.edu> @ 2011-03-03 17:50 ` Urs Schreiber 0 siblings, 0 replies; 3+ messages in thread From: Urs Schreiber @ 2011-03-03 17:50 UTC (permalink / raw) To: Categories mailing list; +Cc: Toby Bartels Dear Vasili; concerning the nLab entry "sieve" http://ncatlab.org/nlab/show/sieve you had written >I am confused about the notion of "encoding" regarding sieves: It seems that I had once used this word in an attempt to express the fact that while the notions of "sieve" (on an object) and "subfunctor" (of the functor represented by that object) are not _identitcal_ notions, one does determine ("encode") the other. Sorry if that wasn't a good formulation. Finn Lawler has meanwhile been so kind to improve the phrasing a bit. By the way, questions and comments about nLab pages are mostly best sent to the community of people who work on that wiki and these people can jointly be contacted by posting a message to the "nForum". There is now for instance a thread discussing your question, which you can see here: http://www.math.ntnu.no/~stacey/Mathforge/nForum/comments.php?DiscussionID=2534&page=1 All the best, Urs [For admin and other information see: http://www.mta.ca/~cat-dist/ ] ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2011-03-03 17:50 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2011-03-01 19:18 sieves in nLab Vasili I. Galchin 2011-03-02 20:04 ` Toby Bartels [not found] ` <20110302200410.GA17666@ugcs.caltech.edu> 2011-03-03 17:50 ` Urs Schreiber
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