18 Answers votes newest views recent 1Constructible topology on schemes 1What is the definition of “canonical” ? 4Galois action on special fiber of a stable model 1Explicit equation of Dickson invariant / quasideterminant / special orthogonal group over the integers 2Top cohomology detecting compactness 2Polynomials for addition in the Witt vectors 0Local rings of non-closed points 2functions satisfying “one-one iff onto” 3universal categorical quotient 2Finiteness of étale Cohomology Groups 2Valuation Criterion of Properness, (Irreducible) Varieties 4Is the category of affine fppf groups closed under normal quotients? 3Is a flat, locally finite type morphism open? 1Criterion for open morphisms without constructible sets? 10Widely accepted mathematical results that were later shown wrong? 6When is the push-forward of the structure sheaf locally free 3Tannaka formalism and the étale fundamental group 4Z_p flatness and irreducible components.