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.

Questions involving results for the special case of matrices over the integers, reals, or complex numbers in which all coefficients are 0 or 1 (e.g. permutation matrices and adjacency matrices of grap…
2 questions
In the earliest days of MathOverflow, there was a '20 questions' seminar (see <http://sbseminar.wordpress.com/category/20-questions/>) run by graduate students at Berkeley. Many questions from the sem…
18 questions
20 questions
a space that locally looks like Euclidean 3-dimensional space
411 questions
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a 4-manifold with a smooth structure. In dimension four, in marked contrast with lower dimensions, topological and smooth manifolds are quite different.
171 questions
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. …
Deprecated; do NOT use this tag. Instead you could consider gr.group-theory, ac.commutative-algebra, ra.rings-and-algebras, universal-algebra, or various more specific tags.
174 questions
Arguments working entirely at a high level of abstraction, particularly category-theoretic arguments.
18 questions
a poset satisfying a list of properties shared by face lattices of polytopes.
13 questions
Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics.
An acyclic orientation of an undirected graph is an assignment of a direction to each edge (an orientation) that does not form any directed cycle and therefore makes it into a directed acyclic graph. …
4 questions
For questions about Adams operations which are cohomology operations for K theory.
8 questions
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,…
468 questions
41 questions
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95 questions
for questions on algebraic geometry, including algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.
For questions about $A_\infty$-algebras as introduced by Stasheff in 1963 and related structures.
81 questions
a 27-dimensional exceptional Jordan algebra.
2 questions
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…
162 questions
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