Jason Polak
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 Sep 21 awarded Yearling Aug 31 comment Prerequisites and references for homological algebra @MathematicalPhysicist: Nearly all the typographical errors (that I could find, of course, and many that I couldn't) of Weibel's text have been listed on his website for some time. Jul 6 comment Free modules are projective. @peterag: Thanks very much! A terrible omission on my part :) Jul 6 revised Free modules are projective. forgot a word Jun 29 comment $M_1$, $M_2$ and $M_1\cap M_2$ injective imply $M_1+M_2$ is also injective? @PtF: Sounds good Jun 29 comment What is $\operatorname{Hom}_R(P,R)$ isomorphic to when $P$ is projective? @user26857: The answer to your question is false, e.g. $\mathrm{Hom}(\oplus^\omega \mathbb{Z},\mathbb{Z})\cong\prod^\omega\mathbb{Z}$. Jun 29 revised $M_1$, $M_2$ and $M_1\cap M_2$ injective imply $M_1+M_2$ is also injective? typo fix Jun 29 answered $M_1$, $M_2$ and $M_1\cap M_2$ injective imply $M_1+M_2$ is also injective? Jun 28 comment Ext$_R^n(Q,A)=0=$Tor$_n^R(Q,A)$ where $Q$ is the field of fractions of a domain $R$ @1234: Yes, that sounds good! However, for the isomorphism part, you can still use the fact that any map $Q\to Q$ extends uniquely up to chain homotopy to the projective resolution. Jun 27 answered Ext$_R^n(Q,A)=0=$Tor$_n^R(Q,A)$ where $Q$ is the field of fractions of a domain $R$ Jun 14 answered functor of points for grassmannian Jun 14 answered Is this a typo in Weibel, page 1? Jun 14 comment In a reduced ring the set of zero divisors equals the union of minimal prime ideals. @EricTowers: Thanks, corrected. Jun 14 revised In a reduced ring the set of zero divisors equals the union of minimal prime ideals. edited body Jun 13 comment In a reduced ring the set of zero divisors equals the union of minimal prime ideals. @user26857 - Didn't notice that, thanks! However, I still feel it's more convenient to have a self-contained solution with notation in line with the entire answer rather than jump to another page with a different notation. Jun 13 answered In a reduced ring the set of zero divisors equals the union of minimal prime ideals. May 6 answered Group theory and Complex Analysis May 4 comment Heuristic: Daniell integral vs. Lebesgue integral A similar question you might find useful: math.stackexchange.com/questions/175991/… Apr 27 comment Vector Bundles：differential geometry vs algebraic geometry I believe a superior source to Hartshorne is Gortz and Wedhorn's "Algebraic Geometry I", chapter 11. Apr 3 comment Examples of real world situations where mathemematical rigour is needed A level of rigour is definitely required for applying statistical results to the real world. You could get an idea of this at the cross validated site....