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Finite or discrete collections of geometric objects. Packings, tilings, polyhedra, polytopes, intersection, arrangements, rigidity.
22
votes
3
answers
821
views
Covering a hexagon
For $\epsilon > 0$ sufficiently small, can a regular hexagon with sides of length $1 + \epsilon$ be covered by seven equilateral triangles with sides of length $1$?
Motivation: Conway and Soifer show …
8
votes
Is there a dense subset of the real plane with all pairwise distances rational?
Victor Klee and Stan Wagon write about this and other fun problems in their book:
Old and New Unsolved Problems in Plane Geometry and Number Theory
2
votes
Erdos-Szekeres in high dimensions
I know that Morris and Soltan's survey article covers some higher-dimensional cases, but I don't remember if they have any bounds of the kind you're asking for.
http://www.ams.org/journals/bull/2000- …
6
votes
1
answer
631
views
How many convex shapes can be made with the pieces of the Stomachion?
Tangrams are a well-known dissection of the square into seven convex polygons. One fun mathematical question is: how many convex rearrangements of the seven pieces are there?
Answer: there are 12 mor …
7
votes
1
answer
355
views
Does the Hirsch conjecture hold for $n < 2d$?
The Hirsch conjecture asserts that the graph (i.e. $1$-skeleton) of a $d$-dimensional convex polytope with $n$ facets has diameter at most $n - d$.
After being open for decades, Francisco Santos has …
39
votes
3
answers
2k
views
Chromatic number of the hyperbolic plane
A notorious problem in combinatorics is the following:
If we color $\mathbb{R}^2$ so that no pair of points at unit distance get the same color, what is the fewest number of colors required?
This numb …
4
votes
Accepted
Average degree of contact graph for balls in a box
Torquato and Stillinger have a recent survey article that discusses some questions like this: Jammed hard-particle packings: From Kepler to Bernal and beyond
They are particularly interested in rand …