Giuseppe Tortorella
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 Jun 9 accepted what are the killing vector fields on a triaxial ellipsoid? Jun 9 comment what are the killing vector fields on a triaxial ellipsoid? I have received two answers that are equally very interesting. My question was not restrictive on the kind of proof. Not being possible multiple choices, I have accepted the first posted answer. Jun 8 comment what are the killing vector fields on a triaxial ellipsoid? Dear Robert Bryant, I like this argument very much: going along the lines of your sketch, I should have the occasion to give a proof in closed-form. Your and Algol's answers are both very exaustive. Thanks you. Jun 8 comment what are the killing vector fields on a triaxial ellipsoid? Dear Algol Thanks a lot for the proper reference, and for the explanation. Jun 8 asked what are the killing vector fields on a triaxial ellipsoid? Jun 3 comment Schwartz space inequality @Feynmaniac: About an approach which doesn't separate the two cases $|x|\ge 2|y|$ and $|x|\le 2|y|$: couldn't it be possible the following proof? 1)use the triangle inequality $|x|\le |y|+|x-y|$, 2)apply the binomial formula to $(|y|+|x-y|)^l$, 3)apply the hypothesis on $g$, and finally $|y|^k\le(1+|y|)^l$, for any $y\in\mathbb{R}$ and $0\le k\le l$. Jun 2 comment Algebraic structures of greater cardinality than the continuum? Dear Qiaochu Yuan: even if not an exact duplicate, the OP could read the answers to the similar question mathoverflow.net/questions/32370/…. Was you refering to it? Jun 1 comment Schwartz space inequality Should not it be Schwartz? Jun 1 revised Schwartz space inequality edited tags Jun 1 revised Number of spanning forests in a graph edited tags May 31 comment Car movement - differential geometry interpretation. Dear Beni Bogosel you could give a look to "Nonholonomic Mechanics and Control" by A.Bloch. May 31 comment Car movement - differential geometry interpretation. Dear jkersch: it could be helpful for someone starting to learn analysis on manifolds, to see the product formula (cf. for example Abraham, Marsden, Ratiu MTA) as justification of the interpretation you give of the Lie bracket of vector fields. I believe that this interpretation is not always presented in introductory texts to smooth manifolds. May 30 comment Kernel of a bundle map Dear Benjamin: Please, Martin and Daniel's remarks, however objectionable, are directed exclusively to the question, and not at all to the questioner. May 30 revised Sobolev space: probably simple ode… edited tags May 30 comment How to prove that a certain action is hamiltonian? @Robert Bryant: Thank you very much for the attention, and the careful historical information. I did not known exactly where, in the work of Elie Cartan, this formula appeared for the first time. Please, my previous observation was just an hypothesis to explain the attribution of this formula to Henri instead than to Elie, as I found it sometimes in the literature. May 29 comment How to prove that a certain action is hamiltonian? @Theo Buehler: Yes surely it is due to the foundational work of Elié Cartan, but I thought it was named after his son Henri Cartan, for this formula is singled out in his axiomatic presentation of the equivariant cohomology for smooth manifolds acted by a Lie group. Precisely, I found it under this name in Symplectic Geometry and Analytical Mechanics of Libermann and Marle. Thanks again for your help with editing and for your suggestion about LaTeX. May 29 comment How to prove that a certain action is hamiltonian? @Theo Buehler: Thanks a lot. May 29 comment How to prove that a certain action is hamiltonian? Please, excuse me, even if I exactly copied the text of the quoted question, here I have some difficulties in visualizing the sketched proof. Do you have the same troubles? May 29 revised How to prove that a certain action is hamiltonian? added 4 characters in body; added 1 characters in body May 29 revised How to prove that a certain action is hamiltonian? trying to correct tex; deleted 5 characters in body