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.

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For questions related to Moebius inversion and its applications.
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For questions about the geometry, complex-analytic, and group-theoretic properties of the Möbius transformations (linear fractional transformations) $z \mapsto \frac{az + b}{cz + d}$ of the complex pl…
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Questions about or involving perfect numbers which are positive integers that are equal to the sum of their proper positive divisors.
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Mental arithmetic comprises arithmetical calculations using only the human brain, with no help from calculators, computers, or pen and paper.
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For questions about the least common multiple of a collection of numbers (or more generally, elements of a commutative ring).
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For questions on determining whether a number is rational, and related problems. If applicable, use this tag instead of (rational-numbers) and (irrational-numbers). Consider adding a tag (radicals) or…
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For questions about torsion groups and their properties. A torsion group is a group in which every element has finite order.
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For questions on Gauss sums, a particular kind of finite sum of roots of unity.
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If the expression obtained after any substitution during limit analysis does not give enough information to determine the original limit, it is known as an indeterminate form.
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For questions about vector lattices (aka. Riesz spaces; a type of vector space equipped with a partial order), Banach lattices and similar topics.
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Computation of Cauchy principal values of integrals. May be tied in with contour integration, but should be separate from definite-integrals.
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The Ricci flow on a Riemannian manifold $(M,g)$ is determined by the geometric evolution equation $\partial_t g_{ij} = -2R_{ij}$ where $R_{ij}$ is the Ricci curvature. The Ricci flow is the main ingre…
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a non-orientable surface. It was first described in 1882 by the German mathematician Felix Klein.
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Kolmogorov complexity concerns the size of the shortest program that generates a given string.
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Questions dealing with set-theoretic functions defined by transfinite recursion.
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For questions about topological graphs, flows, representation, planar, and book embeddings, geometric graphs, crossing numbers, coloring graphs, and other topics in topological graph theory.
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Probabilistic methods prove existence results in a nonconstructive fashion, by showing the chance of randomly selecting a solution is greater than zero.
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For questions regarding profinite groups and their properties.
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meromorphic functions on $\mathbb{C}$ that are used extensively in number theory
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a regular, convex polyhedron with congruent faces of regular polygons and the same number of faces meeting at each vertex.
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For questions related to the fractional part of a number.
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typically defined to be without boundaries (every point has a neighbourhood homeomorphic to an Euclidean open disc). Use this tag for the manifolds with boundaries, as well as manifolds …
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For questions regarding the formal analysis of collective decision problems.
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For questions about three-valued logic and other non-classical logics. Please use the more specific tags 'modal-logic' and 'fuzzy-logic' instead of this tag if they apply.
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For questions about Octave, a high-level interpreted language for numerical computations.
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Percolation theory describes the behavior of connected clusters in a random graph.
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