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bio website jmilne.org/math
location Ann Arbor, MI, USA, and New Zealand.
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visits member for 4 years, 10 months
seen Oct 18 '10 at 13:35
Arithmetic geometry (especially Shimura varieties and abelian varieties).

May
31
comment What was Galois theory like before Emil Artin?
Actually, it wasn't all that different, except that you first proved the primitive element theorem, and then proved things by choosing a primitive element. Artin disliked having to make a choice, and his main contribution was show that you can do Galois theory without choosing a primitive element. It's not obvious to me that this makes things easier or better. You can find the old approach in A.A. Albert's book on algebra.
May
29
comment Points of reductive groups
Actually, "Deligne's result" is already in Saavedra, and the reference given is to an article by Deligne and somebody else.
May
27
revised Automorphism of algebraic group preserving a hyperspecial maximal compact
added 482 characters in body
May
26
answered Automorphism of algebraic group preserving a hyperspecial maximal compact
May
26
comment Ext of Tate-modules of abelian varieties
Over a finite field, these Ext groups are studied in one of my 1968 Inventiones papers. The same techniques may work over local fields.
May
20
revised Constructing coherent sheaves on Shimura varieties.
added 7 characters in body
May
20
answered Constructing coherent sheaves on Shimura varieties.
May
15
comment Motives versus Motifs
I've quite often seen the English word "motif" (meaning A distinctive, significant, or dominant idea or theme...) written "motive", which is one reason I chose as the title of LNM 900 "Hodge cycles, Motives,..." (at the time both "motive" and "motif" were in use in English). I would prefer to say that the French word "motif" has been borrowed three times into English, and twice anglicized.
May
14
comment Quotients of Abelian Varieties by Finite Groups
The group of automorphisms of a polarized abelian variety is finite, and Shimura and Taniyama (in their famous 1961 book, p35) define a Kummer variety to be the quotient of a polarized abelian variety by the full group of automorphisms. For a general polarized abelian variety, the automorphism group is Z/2Z, and so I expect that they have been most studied in that case.
May
14
answered If Erdős is published as Erdös in a paper, which do I cite?
May
12
comment homology of abelian variety ?
Perhaps its the paper that includes: "Recall that the category of abelian varieties up to isogeny is obtained from the category of abelian varieties by taking the same class of objects but replacing $Hom(A,B)$ with $Hom(A;B)\otimes\mathbb{Q}$. We shall always regard an abelian variety as an object in the category of abelian varieties up to isogeny: thus $Hom(A,B)$ is a vector space over $\mathbb{Q}$." If so, $A\otimes E$ means $A\otimes_{\mathbb{Z}}\mathcal{O}_{E}$, which is explained by Torsten.
May
12
comment What are examples of mathematical concepts named after the wrong people? (Stigler's law)
It's not so clear. In the historical notes to his book, Nagata says that in the case N=0 and M an ideal, the lemma was given by Krull, and that the general case is in a paper of Azumaya. But Nagata learned it from Nakayama and Azumaya when he was an undergraduate. Since some mathematicians were calling it Nakayama's lemma, he asked Nakayama who had this formulation first, to which Nakayama responded that he did not remember whether Nakayama or Azumaya was the first. Probably it should be considered folklore, and the name "Nakayama's lemma" seems appropriate.
May
12
comment Representations of reductive Lie group
There's a complete proof that representations of reductive groups in characteristic zero are semisimple in II, section 5, of the notes on my website.
May
9
comment Question about computing group cohomology using cochains
For a group (no topology), I define the cohomology using injective resolutions in the category of all G-modules, and I prove that it can be computed using cochains (no conditions on G). For a profinite group, I define the cohomology using injective resolutions in the category of all discrete G-modules, and state that it can be computed using continuous cochains. A finite group can be regarded as a profinite group with the discrete topology, in which case the two definitions coincide (obviously).
May
8
comment Examples of common false beliefs in mathematics
Pete: It can screw you up very badly. For example, F-isocrystals are very different over the maximal unramified extension of Q_p and its completion.
May
7
comment Published results: when to take them for granted?
Actually, the signs in Deligne's Travaux de Shimura are correct. It's in his Corvallis article that he got them wrong...
May
6
comment Why are normal crossing divisors nice?
Hironaka proved that a smooth variety can always be realized as an open subvariety of a smooth projective variety in such a way that the boundary is a divisor with normal crossings.
May
5
answered Lifting Etale Morphisms
Apr
18
comment Is there a schemetical construction for modular curves over the rationals?
"I agree PVHS is the way to prove analyticity (but not evident to beginners" well, they could try reading [the next version] of my Introduction to Shimura Varieties. More seriously, this argument in the one-dimensional case is pretty trivial, and Katz and Mazur were surely aware of it, so I find the statement in your first comment a bit strong. Perhaps they considered it too obvious to write out (or just forgot).
Apr
18
comment Is there a schemetical construction for modular curves over the rationals?
I'm not sure I understand Brian's objections --- Shimura worked a lot with function fields and really did prove things. However, I would agree that this is completely the wrong way to do things.