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Dec 28, 2021 at 9:08 comment added Cranium Clamp @Z.M I found most of the details of that relative second cohomology group and the integral (which is $ \zeta(2) $) in the paper of Francis Brown here: arxiv.org/abs/math/0606419
Dec 27, 2021 at 16:39 comment added Z. M Periods are more general than that (I am not sure whether this kind of "periods" also dates back to the 19th century). Kontsevich–Zagier gave several examples like $\log(2)$ and $\zeta(3)$ right after the first definition. The MO question that OP linked also contains an example $\int_{0\le x\le y\le1}(1-x)^{-1}y^{-1}\mathrm{d}x\mathrm{d}y$, but I don't understand their $H^2(\overline{M_{0,5}}\setminus A,B\setminus(A\cap B))$.
Dec 27, 2021 at 16:05 comment added Misha Verbitsky If I understand correctly, you should take the Riemann surface of this function in the complex 2-space with coordinates (x, y), and integrate the form dx/y along the path which lifts this interval to one branch until the branching point, then goes around this point and goes back along another lift of this interval, but on a different branch.
Dec 27, 2021 at 15:58 comment added Misha Verbitsky There is a detailed argument in this paper arxiv.org/pdf/1504.04405.pdf The Origins of Complex Geometry in the 19th Century (Raymond O. Wells, Jr.), Section 6
Dec 24, 2021 at 23:14 comment added Z. M Sorry for a silly question: how to rewrite $\int_0^r\mathrm{d}x/\sqrt{4x^3-ax-b}$ (in the second of the original post) as an integral over a closed cycle on a Riemann surface?
Dec 24, 2021 at 14:32 history edited Misha Verbitsky CC BY-SA 4.0
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Dec 24, 2021 at 9:43 vote accept Cranium Clamp
Dec 23, 2021 at 12:13 history answered Misha Verbitsky CC BY-SA 4.0