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    • CommentRowNumber1.
    • CommentAuthorYaron
    • CommentTimeFeb 23rd 2012

    Started presentation of a category by generators and relations. This is probably an evil definition (there was an old discussion on this in the context of quotient category), and there is perhaps a more modern way to do this, so feel free to change the entry. I used “quotient category” as in CWM and mentioned that this is not the definition in the nLab.

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeFeb 23rd 2012
    • (edited Feb 23rd 2012)

    By the way, I recently repeatedly came to think that we should have a general entry titled generators and relations which explains the idea first in full generality (e.g. free construction followed by quotient) and then lists examples.

    Because I noticed that we have many entries whose definitions invoke “generators and relations” and strictly speaking they should all point to an explanation for what precisely that means.

    • CommentRowNumber3.
    • CommentAuthorMike Shulman
    • CommentTimeFeb 23rd 2012

    @Yaron: thanks! I added some links from a few places.

    @Urs: That’s an excellent idea! I made a start: generators and relations.

    • CommentRowNumber4.
    • CommentAuthorTim_Porter
    • CommentTimeFeb 24th 2012

    I have added a brief reference to the links with computads and 2-polygraphs, and also to Mitchell’s paper on Rings with several objects which has a neat section on this.

    • CommentRowNumber5.
    • CommentAuthorTobyBartels
    • CommentTimeFeb 26th 2012

    I added a bit to generators and relations, including mention of finitely presented objects (and a link back from there).

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