User quetzalcube - MathOverflow most recent 30 from http://mathoverflow.net 2013-05-21T23:56:09Z http://mathoverflow.net/feeds/user/12204 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/130689/reference-for-cech-cohomology-for-nisnevich-topology Reference for Cech cohomology for Nisnevich topology Quetzalcube 2013-05-15T10:06:32Z 2013-05-15T10:06:32Z <p>I need the theorems that prove that Nisnevich cohomology can be computed by the Cech complex similar to what happens in the étale topology. </p> <p>I know this has to be true since (Morel-Voevodsky: $\mathbb{A}^1$-homotopy theory of schemes. Publ. Math. IHES (1999)) say it at the beggining of sectio 3, page 95... but they don't give the reference!</p> <p>Thank you very much for your help!</p> http://mathoverflow.net/questions/91312/why-are-kan-fibrations-and-serre-fibrations-so-important Why are Kan fibrations and Serre fibrations so important? Quetzalcube 2012-03-15T17:23:34Z 2012-03-16T09:05:28Z <p>I know so far that Kan fibrations are the abstract analog of Serre fibrations but i don't have any expierience with neither one of them so </p> <p>Could someone give a motivation why Kan fibrations (or if easier, Serre fibrations) are so important in homotopy theory of simplicial sets?</p> <p>Thank you</p> http://mathoverflow.net/questions/78314/alexander-duality-theorem-for-cw-complexes-and-stable-homotopy-theory Alexander duality theorem for CW-complexes and stable homotopy theory Quetzalcube 2011-10-17T07:40:31Z 2011-10-31T03:54:43Z <p>In Adams, J.F. <em>Infinite Loop Spaces</em> Princ. Univ. Press. page 9 he states Alexander duality theorem </p> <p><strong>Theorem:[Alexander Duality]</strong> $$H^r(X,G)=H_{n-r+1}(S^n-X,G)$$</p> <p>for finite CW-complexes with a "nice embedding". That is to say, $S^n-X$ has a CW-complex $Y$ as deformation retract and $X$ is a deformation retract of $S^n-Y$.</p> <p>My first question is the following: <strong>Do you know if every CW-complex admits a nice embedding into some $S^n$?</strong> if so, <strong>could you give a reference?</strong></p> <p>Thanks in advance.</p> http://mathoverflow.net/questions/54186/reference-learning-noncommutative-geometry-and-c-algebras Reference: Learning noncommutative geometry and C^* algebras Quetzalcube 2011-02-03T11:27:41Z 2011-02-05T02:55:33Z <p>I am starting to study noncommutative geometry and C^* algebras so my question is</p> <p><strong>Does anyone knows a good reference on this subject?</strong></p> <p>I would like a basic book with intuitions for definitions and this kind of things. I come from algebraic geometry so if it talks a bit about the relation with it would be highly appreciated.</p> <p>I have already taken a look to Conne's book but I find it too hard and I'm currently studying Landi's but it lacks lots of proofs (he refers to several papers)</p> <p>Thanks in advance</p> http://mathoverflow.net/questions/51991/are-finite-correspondances-flat Are finite correspondances flat? Quetzalcube 2011-01-13T19:04:21Z 2011-01-14T14:10:01Z <p>In Voevodsky&amp;Mazza&amp;Weibel's book on motivic cohomology they define "an <strong>elementary correspondance</strong> from <em>X</em> (Smooth connected scheme over $k$) to <em>Y</em> (separated scheme over $k$) as an irreducible closed subset $W$ of $X\times Y$ whose associated integral subscheme is finite and surjective over $X$."</p> <p>As far as I know $W$ would be flat over $X$ if it was Cohen-Macaulay so...</p> <p><strong>1.- ¿Is $W$ flat over $X$?</strong></p> <p>If not,</p> <p><strong>2.- why isn't this a common sense assumption? Could anyone give an example of why nonflat elementary correspondaces should be allowed?</strong></p> <p>Thanks in advance</p> http://mathoverflow.net/questions/130689/reference-for-cech-cohomology-for-nisnevich-topology Comment by Quetzalcube Quetzalcube 2013-05-17T07:49:59Z 2013-05-17T07:49:59Z Oups, you are right. Thank you very much. Prop. 3.1.9 is actually what i was looking for. Sorry for my mistake! http://mathoverflow.net/questions/461/understanding-steenrod-squares/19713#19713 Comment by Quetzalcube Quetzalcube 2011-06-14T14:15:13Z 2011-06-14T14:15:13Z $v$ is the normal bundle sorry ( i don't how to &#233;rase the comment) but still: what is $w_i$? thanks http://mathoverflow.net/questions/461/understanding-steenrod-squares/19713#19713 Comment by Quetzalcube Quetzalcube 2011-06-14T14:10:09Z 2011-06-14T14:10:09Z please, could you define what is $w_i$ and $v$ in the formula $Sq^i(x)=f_*(w_i(v))$? Thanks a lot in advance