# Recent Activity

## Divisibility of central binomial coefficients ★★

Author(s): Graham

**Problem (1)**Prove that there exist infinitely many positive integers such that

**Problem (2)**Prove that there exists only a finite number of positive integers such that

Keywords:

## ¿Are critical k-forests tight? ★★

Author(s): Strausz

**Conjecture**

Let be a -uniform hypergraph. If is a critical -forest, then it is a -tree.

Keywords: heterochromatic number

## Saturated $k$-Sperner Systems of Minimum Size ★★

Author(s): Morrison; Noel; Scott

**Question**Does there exist a constant and a function such that if , then every saturated -Sperner system has cardinality at least ?

Keywords: antichain; extremal combinatorics; minimum saturation; saturation; Sperner system

## List Colourings of Complete Multipartite Graphs with 2 Big Parts ★★

Author(s): Allagan

**Question**Given , what is the smallest integer such that ?

Keywords: complete bipartite graph; complete multipartite graph; list coloring

## Generalised Empty Hexagon Conjecture ★★

Author(s): Wood

**Conjecture**For each there is an integer such that every set of at least points in the plane contains collinear points or an empty hexagon.

Keywords: empty hexagon

## General position subsets ★★

Author(s): Gowers

**Question**What is the least integer such that every set of at least points in the plane contains collinear points or a subset of points in general position (no three collinear)?

## Forcing a 2-regular minor ★★

**Conjecture**Every graph with average degree at least contains every 2-regular graph on vertices as a minor.

Keywords: minors

## Fractional Hadwiger ★★

Author(s): Harvey; Reed; Seymour; Wood

**Conjecture**For every graph ,

(a)

(b)

(c) .

Keywords: fractional coloring, minors

## Generalized path-connectedness in proximity spaces ★★

Author(s): Porton

Let be a proximity.

A set is connected regarding iff .

**Conjecture**The following statements are equivalent for every endofuncoid and a set :

- \item is connected regarding . \item For every there exists a totally ordered set such that , , and for every partion of into two sets , such that , we have .

Keywords: connected; connectedness; proximity space

## Direct proof of a theorem about compact funcoids ★★

Author(s): Porton

**Conjecture**Let is a -separable (the same as for symmetric transitive) compact funcoid and is a uniform space (reflexive, symmetric, and transitive endoreloid) such that . Then .

The main purpose here is to find a *direct* proof of this conjecture. It seems that this conjecture can be derived from the well known theorem about existence of exactly one uniformity on a compact set. But that would be what I call an indirect proof, we need a direct proof instead.

The direct proof may be constructed by correcting all errors an omissions in this draft article.

Direct proof could be better because with it we would get a little more general statement like this:

**Conjecture**Let be a -separable compact reflexive symmetric funcoid and be a reloid such that

- \item ; \item .

Then .

Keywords: compact space; compact topology; funcoid; reloid; uniform space; uniformity

## Dirac's Conjecture ★★

Author(s): Dirac

**Conjecture**For every set of points in the plane, not all collinear, there is a point in contained in at least lines determined by , for some constant .

Keywords: point set

## Roller Coaster permutations ★★★

Let denote the set of all permutations of . Let and denote respectively the number of increasing and the number of decreasing sequences of contiguous numbers in . Let denote the set of subsequences of with length at least three. Let denote .

A permutation is called a *Roller Coaster permutation* if . Let be the set of all Roller Coaster permutations in .

**Conjecture**For ,

- \item If , then . \item If , then with .

**Conjecture (Odd Sum conjecture)**Given ,

- \item If , then is odd for . \item If , then for all .

Keywords:

## Rota's basis conjecture ★★★

Author(s): Rota

**Conjecture**Let be a vector space of dimension and let be bases. Then there exist disjoint transversals of each of which is a base.

Keywords: base; latin square; linear algebra; matroid; transversal

## Graphs of exact colorings ★★

Author(s):

Conjecture For , let be the statement that given any exact -coloring of the edges of a complete countably infinite graph (that is, a coloring with colors all of which must be used at least once), there exists an exactly -colored countably infinite complete subgraph. Then is true if and only if , , or .

Keywords:

## Imbalance conjecture ★★

Author(s): Kozerenko

**Conjecture**Suppose that for all edges we have . Then is graphic.

Keywords: edge imbalance; graphic sequences

## Every metamonovalued reloid is monovalued ★★

Author(s): Porton

**Conjecture**Every metamonovalued reloid is monovalued.

Keywords:

## Every metamonovalued funcoid is monovalued ★★

Author(s): Porton

**Conjecture**Every metamonovalued funcoid is monovalued.

The reverse is almost trivial: Every monovalued funcoid is metamonovalued.

Keywords: monovalued

## Decomposition of completions of reloids ★★

Author(s): Porton

**Conjecture**For composable reloids and it holds

- \item if is a co-complete reloid; \item if is a complete reloid; \item ; \item ; \item .

Keywords: co-completion; completion; reloid

## List Total Colouring Conjecture ★★

Author(s): Borodin; Kostochka; Woodall

**Conjecture**If is the total graph of a multigraph, then .

Keywords: list coloring; Total coloring; total graphs

## Partitioning the Projective Plane ★★

Author(s): Noel

Throughout this post, by *projective plane* we mean the set of all lines through the origin in .

**Definition**Say that a subset of the projective plane is

*octahedral*if all lines in pass through the closure of two opposite faces of a regular octahedron centered at the origin.

**Definition**Say that a subset of the projective plane is

*weakly octahedral*if every set such that is octahedral.

**Conjecture**Suppose that the projective plane can be partitioned into four sets, say and such that each set is weakly octahedral. Then each is octahedral.

Keywords: Partitioning; projective plane