Lines and pairs of points on cubics

 Ill talk about a joint work with Evgeny Shinder. We establish a
 relation between a variety of lines and a symmetric square of a cubic
hypersurface. The relation holds in the Grothendieck ring of
varieties, so in particular it proves there are 27 lines on smooth
cubic surface (and some other numbers for surfaces with
 singularities), computes Hodge numbers for varieties of lines, etc.