28 Answers votes newest views recent 9Awfully sophisticated proof for simple facts (2) 3Best online mathematics videos? (2) 34Suggestions for good notation 13Most striking applications of category theory? 19nontrivial theorems with trivial proofs 48Blackbox Theorems (2) 1Combinatorial results without known combinatorial proofs 0When does ‘positive’ imply ‘sum of squares’? 2Subspaces of finite codimension in Banach spaces 9Things that should be positive integers…really? 6Graded local rings versus local rings 3Applications of the “other” definition of Sheaves 7Characterizing specific “concrete” mathematical objects by abstract general properties 15What is the general geometric interpretation of modules in algebraic geometry? 1Does a locally free sheaf over a product pushforward to a locally free sheaf? 5Is the direct image of a constant sheaf a constant sheaf? 0Does the Riemann-Hilbert Correspondence work at the DG level? 8Can we define homotopy groups using Tannakian categories 7Unit ideal in non-commutative rings 2intermediate/middle extension of perverse sheaves 4moduli problem for flag varieties? 2Has there been any application of tensor species? 3Which commutative algebras admit a nonzero Poisson bracket? 1A_infinity structure on cohomology and the weight filtration 6Intersection of all normalizers 1Distinguished triangle of closed - open partition, for D-modules 1Differential operators on M/G are factor of invariant differential operators on M ? (Quantization commute with reduction ) What is state of art ? 8Faithfulness of derived functor.