# Tags

A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

 Type to find tags:
 20-questions× 18 In the earliest days of MathOverflow, there was a '20 questions' seminar (see ) run by graduate students at Berkeley. Many questions from the sem… 2-categories× 16 2-knots× 15 3-manifolds× 268 4-manifold 4-manifolds× 100 abc-conjecture× 19 abelian-categories× 72 abelian-groups× 81 abelian-schemes× 27 abelian-varieties× 391 projective algebraic varieties endowed with an Abelian group structure. Over the complex numbers, they can be described as quotients of a vector space by a lattice of full rank. … absolute-galois-group× 35 abstract-algebra× 283 Do NOT use this tag. Instead you could consider gr.group-theory, ac.commutative-algebra, ra.rings-and-algebras or various more specific tags. abstract-nonsense× 10 Arguments working entirely at a high level of abstraction, particularly category-theoretic arguments. abstract-polytopes× 6 a poset satisfying a list of properties shared by face lattices of polytopes. ac.commutative-algebra× 2562 Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics. accessible-categories× 8 acyclic-orientations× 2 adams-operations× 3 additive-combinatorics× 260 Questions on the subject additive combinatorics, also known as arithmetic combinatorics, such as questions on: additive bases, sum sets, inverse sum set theorems, sets with small doubling, Sidon sets,… ade-classifications× 11 adeles× 23 adjacency-matrices× 5 adjacency-matrix adjoint-functors× 71 admissible-representation× 5 advice× 75 affine-geometry× 21 affine-grassmannian× 21 ag.algebraic-geometry× 10635 Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology. a-infinity-algebras× 40 For questions about $A_\infty$-algebras as introduced by Stasheff in 1963 and related structures. albert-algebras× 2 a 27-dimensional exceptional Jordan algebra. alexandrov-geometry× 100 Alexandrov geometry studies non smooth analogues of Riemannian manifolds with curvature bounded from below or above. It includes spaces with curvature bounded below (briefly $\mathrm{CBB}[\kappa]$) an… algebraic-combinatorics× 82 algebraic-complexity× 9 algebraic-curves× 500 An algebraic curve or plane algebraic curve is the set of points on the Euclidean plane whose coordinates are zeros of some polynomial in two variables.