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 Aug 19 awarded Notable Question Jul 2 awarded Curious Nov 8 awarded Nice Answer Jun 25 awarded Revival Dec 21 awarded Yearling Nov 15 awarded Nice Question Dec 22 awarded Yearling Apr 3 awarded Nice Answer Feb 10 awarded Popular Question Dec 22 awarded Yearling Sep 7 awarded Nice Answer May 17 comment Restriction of a complex polynomial to the unit circle [deleted the comment referred to in the OP's comment from Mar. 5, 4:37] May 17 comment What is the “right” universal property of the completion of a metric space? [deleted previous comments] May 17 comment What is the “right” universal property of the completion of a metric space? [deleted previous comments] May 17 comment Practical applications of algebraic number theory? I honestly don't know [deleted previous comment] May 17 comment Given a finite field $K$, what are the possible degrees of a polynomial $p\in K[x]$ such that $x\longmapsto p(x)$ is one-to-one? There seem to be some discussion on the subject of permutation polynomials in Ch. 7 of Lidl-Niederreiter‏ (books.google.com/…). [I hope I understood the question correctly. In the title shouldn’t $x\mapsto f(x)$ really be $c\mapsto f(c)$?] May 15 comment Reference request for category theory works which quickly prove the theorem which generalises the 1st isomorphism theorem for groups/rings/… Perhaps instead of category theory, you should look at some basic book on universal algebra, for example, you can try part 3 of Cohn’s algebra. May 14 comment is the presheaf category of a locally small category locally small? Thanks for the pointers! The link doesn't seem to work, but I will look at nLab now that I know what to look for. I suppose that at the moment (before finished reading Mac Lane) I'll stick to the foundations described in Section 1.6 of Mac Lane. Although limited (as I now see..), these foundations seem to be sufficient in Mac Lane (as Mike Shulman told me in a comment...), and I should probably not "dive" into something else right now. Thanks again for your help. May 14 comment is the presheaf category of a locally small category locally small? Thank you very much! Having such tips from an expert is extremely helpful. I have a million more question to ask, but I guess these comments aren't the right place for such a mini course... May 14 comment is the presheaf category of a locally small category locally small? Thank you very much for your answer! I hope it is OK that I ask another silly question: Is my comment above correct, but just useless, because (for some reason that I still don't understand) "locally small" can refer to non-small hom-sets that are in bijection with small sets? [I'm assuming a single universe, as in Mac Lane.]