17 Answers votes newest views recent 11Algebraic de Rham cohomology vs. analytic de Rham cohomology 18Why is an injective quasi-coherent sheaf’s restriction to an open subset still an injective object? 16Where does the splitting principle come from and does it generalize 11In what topology DM stacks are stacks 4How ugly is the isomorphism R[GxH] = R[G] (X) R[H] for groups G, H? 8Derived categories of (coherent) sheaves of modules: exceptional images, gluing, and proper descent? 3Proving interesting theorems about S_n using its character table. 7H-space structure on infinite projective spaces 11Interdependence between A^1 homotopy theory and algebraic cobordism 6Constructible sheaves and dg-modules 6Gerbes for a cyclic group. (or maybe G_m too) 9Extraordinary cohomology as a derived functor? 6Cyclic spaces and S^1-equivariant homotopy theory 5Whitehead Products without Base Points? 6Flatness of relative canonical bundle 8characterization of cofibrations in CW-complexes with G-action 8Can Deligne-Mumford stacks be characterized by their restriction to a small subcategory?