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: 
algebraicgroups× 652 
oa.operatoralgebras× 651
Algebras of operators on Hilbert space, C^*algebras, von Neumann algebras, noncommutative geometry

finitegroups× 633 
ho.historyoverview× 630
Biographies, philosophy of mathematics, mathematics education, recreational mathematics, communication of mathematics

polynomials× 629
Questions in which polynomials (single or several variables) play a key role. It is typically important that this tag is combined with other tags; polynomials appear in very different contexts. Please…

riemanniangeometry× 612
a subfield of Differential Geometry, which specifically studies "Riemannian Manifolds", manifolds with "Riemannian Metrics", which means that they are equipped with continuous i…

algorithms× 609  arithmeticgeometry× 591 
primenumbers× 577
Questions where prime numbers play a keyrole, such as: questions on the distribution of prime numbers (twin primes, gaps between primes, Hardy–Littlewood conjectures, etc); questions on prime numbers…

na.numericalanalysis× 554
Numerical algorithms for problems in analysis and algebra, scientific computation

computationalcomplexity× 550
computational complexity theory; complexity classes, such as P, NP, PSPACE, and so on; resourcelimited computation; NPcompleteness and other completeness concepts; oracle analogues of complexity cla…

stochasticprocesses× 547
a collection of random variables usually indexed by a totally ordered set.

sg.symplecticgeometry× 533
Hamiltonian systems, symplectic flows, classical integrable systems

ellipticcurves× 517
an algebraic curve of genus one with some additional properties. Questions with this tag will often have the toplevel tags nt.numbertheory or ag.algebraicgeometry in addition; …

differentialequations× 508
Ordinary or partial differential equations. Delay differential equations, neutral equations, integrodifferential equations. Wellposedness, asymptotic behavior, and related questions.

fourieranalysis× 475 
algebraicnumbertheory× 464 
biglist× 464
Questions designed to generate a "big list" of certain results, examples, conjectures, etc. via many individual answers, each contributing one or a few instances. Such a question should typically be i…

differentialtopology× 457
The study of differentiable manifolds and differentiable maps. One fundamental problem is that of classifying manifolds up to diffeomorphism. Differential topology is what Poincaré understood as topol…

modularforms× 457
Questions about modular forms and related areas

cohomology× 446 
analyticnumbertheory× 440
A beautiful blending of real/complex analysis with number theory. The study involves distribution of prime numbers and other problems and helps giving asymptotic estimates to these.

tagremoved× 435
to be used only when retagging highly(!) offtopic questions where none of the actual tags would make sense; all actual tags the questioner has used are removed and something is needed to…

oc.optimizationcontrol× 407
Operations research, linear programming, control theory, systems theory, optimal control, game theory

modeltheory× 403
the branch of mathematical logic which deals with the connection between a formal language and its interpretations, or models.

banachspaces× 402
a complete normed vector space: A vector space equipped with a norm such that every Cauchy sequence converges.

qa.quantumalgebra× 395
Quantum groups, skein theories, operadic and diagrammatic algebra, quantum field theory

complexanalysis× 374 
knottheory× 361
dealing with embedding of curves in manifolds of dimension 3. A knot is a single circle embedded in the affine space of dimension 3 as a smooth curve not crossing itself. Many knot inva…

algebraiccurves× 359  probabilitydistributions× 353  modulispaces× 334 
computabilitytheory× 330
computable sets and functions, Turing degrees, c.e. degrees, models of computability, primitive recursion, oracle computation, models of computability, decision problems, undecidability, Turing jump, …

highercategorytheory× 329 
kt.ktheoryhomology× 324
Algebraic and topological Ktheory, relations with topology, commutative algebra, and operator algebras

smoothmanifolds× 318 