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Results tagged with co.combinatorics
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user 23571
Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.
4
votes
Accepted
Discriminants of indefinite integral binary quadratic forms admitting 3 or 6 torsion.
The structure of the automorphism group becomes clear when one looks at the Conway topograph of a given form. For an indefinite form not representing 0 the topograph has an infinite periodic river se …
- 20k
35
votes
Why do wedges of spheres often appear in combinatorics?
This is indeed a mystery. I presume the question refers to wedges of spheres of the same dimension, where there's a simple criterion (n-dimensional and (n-1)-connected, for some n). For wedges of sph …
- 20k