Where can I find a proof of the de Rham-Weil theorem? - MathOverflow most recent 30 from http://mathoverflow.net 2013-05-23T04:56:36Z http://mathoverflow.net/feeds/question/91385 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/91385/where-can-i-find-a-proof-of-the-de-rham-weil-theorem Where can I find a proof of the de Rham-Weil theorem? Samuel Mf 2012-03-16T16:39:35Z 2012-03-17T10:21:31Z <p>Where can I find a proof of the de Rham-Weil theorem? </p> <p>Does anyone know?</p> http://mathoverflow.net/questions/91385/where-can-i-find-a-proof-of-the-de-rham-weil-theorem/91399#91399 Answer by Steven Landsburg for Where can I find a proof of the de Rham-Weil theorem? Steven Landsburg 2012-03-16T18:11:23Z 2012-03-16T18:11:23Z <p>If "the de Rham-Weil Theorem" means that you can compute cohomology using acyclic resolutions rather than injective ones, this is a standard result you can find in just about any book on homological algebra. The earliest reference I know is Grothendieck's Tohoku paper, Section 2.4.</p> http://mathoverflow.net/questions/91385/where-can-i-find-a-proof-of-the-de-rham-weil-theorem/91418#91418 Answer by Roger Godement for Where can I find a proof of the de Rham-Weil theorem? Roger Godement 2012-03-16T22:14:05Z 2012-03-16T22:14:05Z <p>Of course Weil did it (although I'm not able to give you the ref right away), and I even lectured on it in Paris 40 years ago. His method is very simple : (1) You first prove that your compact manifold X can be endowed with a Riemann structure (obvious locally, global result by using a smooth partition of unity). (2) By the general theory of Riemann spaces, there are plenty of "convex" open sets U in X, i.e. such that any two points of U can be joined by one and only geodesic arc in U. Such an open set is clearly homotopic to a point, so that every closed diff form on it is exact; the intersection of any two such "convex" sets is also convex. (3) That being said, choose a finite covering of X by convex open sets U(i) - no math available - and let omega (idem) be a form of degree p on X. There are forms omega(i) of degree p-1 in the U(i) such that omega = d[omega(i)] in U(i). Since U(i) inter U(j) = U(i,j) is convex, there are forms omega(i,j) of degree p-2 in the U(i,j) such that omega(j) - omega(i) = d[omega(i,j)] in U(i,j). By standard de Rham, there are forms omega(i,j,k) in the U(i,j,k) = U(i) inter U(j) inter U(k) such that omega(j,k) - omega(i,k) + omega(i,j) = d[omega(i,j,k)] in U(i,j,k), and so on. In this way, you eventually get forms of degree O whose alternate sums are closed, hence CONSTANTS, in the p to p intersections of the U(i). If you consider the abstract simplicial complex defined by the covering (U(i)), i.e. its so-called "nerve" (nerf in French), you thus associate to omega a cocyle of degree p (with real coefficients) of this complex. Etc, etc. You can do it all by your little self - matter of patience.</p> <p>Before Grothendieck's Tohoku, there was a Cartan Seminar on sheaves theory (ca. 1948-49) in which everybody, at any rate in France, learned the theory, including Groth and myself. I even wrote a book on the subject (Théorie des Faisceaux, Paris, Hermann, 1957), which was still on sale (and found customers) two or three years ago, and possibly still is. </p> <p>Don't infer from my answer I'm still doing mathematics. Roger Godement, Paris. </p> http://mathoverflow.net/questions/91385/where-can-i-find-a-proof-of-the-de-rham-weil-theorem/91424#91424 Answer by Liviu Nicolaescu for Where can I find a proof of the de Rham-Weil theorem? Liviu Nicolaescu 2012-03-16T22:28:02Z 2012-03-17T10:21:31Z <p><em>Andrew Fanoe</em>, a former student of mine, wrote his senior thesis on various proofs of the DeRham theorem. In particular he discusses in detail Weil's very elegant proof of DeRham's theorem. Andrew's presentation uses a more modern language, but all the ideas are in Weil's paper. In any case, <a href="http://www.nd.edu/~lnicolae/Fanoethesis.pdf" rel="nofollow">here is the link to Andrew's thesis.</a> It's worth having a look at it. It is well written and may have references you might find useful.</p>