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Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.

7 votes
1 answer
204 views

Are the primary parallelotopes classified? (equivalently, Voronoi cells of lattices)

A primary parallelohedron is a polyhedron that can fill space with infinite translated copies. It is known (e.g., Coxeter, H. S. M. Regular Polytopes, 3rd ed. New York: Dover, pp. 29-30, 1973; or, Tu …
Samuel Reid's user avatar
  • 1,441
7 votes
2 answers
547 views

Kissing Number of Spheres in Non-Euclidean Geometry

There has been much work done on the kissing number problem (of determining the greatest number of congruent spheres which can touch a single sphere in a packing) in Euclidean space for dimensions $1$ …
Samuel Reid's user avatar
  • 1,441
4 votes
2 answers
356 views

Finding the order of a flip graph and how it relates to all possible triangulations of a graph

I've recently run into the following problem: Given a planar graph, how many possible triangulations are there? I am using triangulations in the normal sense when applied to anything in geometri …
Samuel Reid's user avatar
  • 1,441
3 votes
1 answer
723 views

Klein Bottle exception to the Heawood Conjecture [duplicate]

Possible Duplicate: The Klein bottle and the Heawood Conjecture It is well known that the Heawood Conjecture states that the bound for the number of colours which are sufficient to colour a m …
Samuel Reid's user avatar
  • 1,441
2 votes
2 answers
281 views

On the Combinatorial Classification of Modal Kripke Frames

We have that S5 modal logic is characterized by the modal axioms $K$, $M$ (reflexive), $4$ (transitive), and $B$ (symmetric). That is, an equivalence relation on a set of possible world (which can be …
Samuel Reid's user avatar
  • 1,441
1 vote
1 answer
497 views

Does the Hardy-Ramanujan Asymptotic Formula Partition Sets or Integers?

From "Models and Games" by Jouko Vaananen (Cambridge studies in advanced mathematics), I quote The Hardy-Ramanujan asymptotic formula says that the number of equivalence relations on a fixed set o …
Samuel Reid's user avatar
  • 1,441
1 vote
1 answer
133 views

Generalizing the internal angle of a graph in $\mathbb{E}^2$ to $\mathbb{S}^2$

I am currently working on research involving packing problems and am finding myself needing the tools from Combinatorial Geometry (in particular, I've been reading Pach and Agarwal's book on the subje …
Samuel Reid's user avatar
  • 1,441
0 votes
Accepted

On the Combinatorial Classification of Modal Kripke Frames

I happened to end up writing a paper which answered my question if anyone else is ever interested in this topic or comes across this question: "On Generalizing a Temporal Formalism for Game Theory to …
Samuel Reid's user avatar
  • 1,441
0 votes
1 answer
145 views

Asymptotics of the Number of Non-Isomorphic Equivalence Relations and the Number of Non-Isom...

The number of non-isomorphic equivalence relations on a set of $n$ elements is the partition function $$p(n) =\frac{1}{\pi\sqrt{2}} \sum_{k=1}^{\infty} \sum_{h=1}^{k} \delta_{\gcd(h,k),1} \text{exp}\l …
Samuel Reid's user avatar
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