most recent 30 from http://mathoverflow.net 2013-05-26T04:19:28Z http://mathoverflow.net/feeds/user/21545 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/89596/on-dehns-infinitesimal-rigidity-theorem guillaume 2012-02-26T18:50:30Z 2012-02-27T00:41:09Z

<p>Dehn's theorem states that any simplicial strictly convex polyedron P in Euclidean 3-space is infinitesimally rigid (that is, any non-trivial first order deformation of P induces a variation of its edges lengths). But many authors write « convex polyhedra are infinitesimally rigid »... Are the conditions « simplicial » and « strictly » necessary ? </p>

http://mathoverflow.net/questions/88922/derivation-of-surfaces/88945#88945 guillaume 2012-02-19T17:28:39Z 2012-02-19T17:28:39Z

<p>For a surface in 3-dimensional Euclidean space, there is an an analogue of the evolute of a curve but ... in Lorentz-Minkowski space-time, not in 3-dimensional Euclidean space :</p> <p>Derivation of convex surfaces of $\Bbb R^3$ in Lorentz space and study of their focals. C. R., Math., Acad. Sci. Paris 348, No. 23-24, 1307-1310 (2010). </p> <p>The author does not consider the case of dimensions greater than 3.</p>