20 Answers votes newest views recent 13Homotopy groups of Lie groups 5Logic comment in Mumford’s Red Book 0Do convolution and multiplication satisfy any nontrivial algebraic identities? 2When are there enough projective sheaves on a space X? 1(∞, 1)-categorical description of equivariant homotopy theory 1What are the higher homotopy groups of Spec Z ? 4D-modules supported on the nilpotent cone 8Which R-algebras are the group ring of some group over a ring R? 17Topologically contractible algebraic varieties 2Making D-modules on affine varieties more explicit 3Understanding the unreducedness of a subscheme supported on fixed points 1Thom first isotopy lemma in o-minimal structures 6Which commutative groups are the group of units of some field? 3Hypercube decomposition of perverse sheaves 6What are the implications of torsion in H^2 for geometric quantization? 3How should I think about correspondences? 2Equivariant Derived Categories via their properties. 1Is there a theory of differential equations for smooth correspondences? 2When is the derived category of representations of a finite poset equivalent to its opposite? 4Over which schemes can there exist non-trivial G_a bundles?