Comments for Stacks Project Blog
http://math.columbia.edu/~dejong/wordpress
Algebraic stacks and open source algebraic geometryMon, 14 Aug 2017 20:34:56 +0000hourly1https://wordpress.org/?v=4.8.1Comment on Mgbar by Johan
http://math.columbia.edu/~dejong/wordpress/?p=4184&cpage=1#comment-1137292
Mon, 14 Aug 2017 20:34:56 +0000http://math.columbia.edu/~dejong/wordpress/?p=4184#comment-1137292All in its own good time, but yes!
]]>Comment on Mgbar by BCnrd
http://math.columbia.edu/~dejong/wordpress/?p=4184&cpage=1#comment-1137291
Mon, 14 Aug 2017 19:26:57 +0000http://math.columbia.edu/~dejong/wordpress/?p=4184#comment-1137291Are you planning to include the proof (via deformation theory?) of the fact that the closed complement of $\mathcal{M}_g$ in $\overline{\mathcal{M}}_g$ is the support of a $\mathbf{Z}$-flat relative effective Cartier divisor (giving a most satisfactory sense in which $\mathcal{M}_g$ is “relatively dense” in $\overline{\mathcal{M}}_g$)? Or something about the story of $\mathcal{M}_{g,n}$ (which is useful in a paper I once read about alterations…)?
]]>Comment on Mgbar by Emmanuel Kowalski
http://math.columbia.edu/~dejong/wordpress/?p=4184&cpage=1#comment-1137290
Mon, 14 Aug 2017 16:31:00 +0000http://math.columbia.edu/~dejong/wordpress/?p=4184#comment-1137290Congratulations!
]]>Comment on Mgbar by Pieter Belmans
http://math.columbia.edu/~dejong/wordpress/?p=4184&cpage=1#comment-1137289
Mon, 14 Aug 2017 16:15:29 +0000http://math.columbia.edu/~dejong/wordpress/?p=4184#comment-1137289Some statistics about the result: it requires 6455 tags (which is 27% of the current toal), in 1493 sections (which is 52% of the sections).
]]>Comment on Yet another update and … by 6000 pages | Stacks Project Blog
http://math.columbia.edu/~dejong/wordpress/?p=4177&cpage=1#comment-1137267
Sun, 09 Jul 2017 18:15:45 +0000http://math.columbia.edu/~dejong/wordpress/?p=4177#comment-1137267[…] ← Previous […]
]]>Comment on Challenge Accepted by Jason Starr
http://math.columbia.edu/~dejong/wordpress/?p=4149&cpage=1#comment-1136702
Sun, 30 Oct 2016 17:26:49 +0000http://math.columbia.edu/~dejong/wordpress/?p=4149#comment-1136702So why doesn’t that work?
]]>Comment on Completeness by Jason Starr
http://math.columbia.edu/~dejong/wordpress/?p=4123&cpage=1#comment-1136324
Sun, 03 Apr 2016 11:01:37 +0000http://math.columbia.edu/~dejong/wordpress/?p=4123#comment-1136324Was this post and April 1 joke? No textbook is complete. In my opinion, no textbook should be “complete”, at least, not if it is going to be used by students to learn a subject for the first time. Once I tried teaching an intro grad course out of a textbook that was written more as an encyclopedia than a textbook. Before each lecture, I spent hours tracing forward through the book trying to determine which baroque lemmas would be used later and which would not. That was not the author’s fault: it was my fault for trying to teach out of a book that was not suitable for classroom use.
]]>Comment on Blowing down exceptional curves by Johan
http://math.columbia.edu/~dejong/wordpress/?p=4115&cpage=1#comment-1136227
Mon, 07 Mar 2016 11:51:45 +0000http://math.columbia.edu/~dejong/wordpress/?p=4115#comment-1136227Sorry, I forgot to say that E is an effective Cartier divisor; I have edited the post. The fact that E is an effective Cartier divisor implies that every local ring of X at a closed point of E is regular of dimension 2. But part of the problem with not assuming more about X is that it need not be the case that X has dimension 2 in an open neighbourhood of E, although I have no counter example.
]]>Comment on Blowing down exceptional curves by Jason Starr
http://math.columbia.edu/~dejong/wordpress/?p=4115&cpage=1#comment-1136224
Mon, 07 Mar 2016 09:38:45 +0000http://math.columbia.edu/~dejong/wordpress/?p=4115#comment-1136224Just so I understand, is the ambient scheme regular of dimension 2, and does it contain $E$ as a Cartier divisor?
]]>Comment on Canonical divisor by Jason Starr
http://math.columbia.edu/~dejong/wordpress/?p=4093&cpage=1#comment-1136187
Thu, 18 Feb 2016 21:23:31 +0000http://math.columbia.edu/~dejong/wordpress/?p=4093#comment-1136187Maybe I am remembering the problem of constructing the relative Todd class as an element in K-theory for perfect morphisms (although presumably that is in SGA 6 . . .). Apart from the Q-coefficients issue (which seems unavoidable), Grothendieck’s formulation (for perfect morphisms, etc.) takes values in a ring formed from K-theory, which could be much bigger than the corresponding Chow groups (which Fulton defines in terms of the associated reduced scheme, so definitely lose information).
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