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

Author(s): Morrison; Noel; Scott

\begin{question} Does there exist a constant $c>1/2$ and a function $n_0(k)$ such that if $|X|\geq n_0(k)$, then every saturated $k$-Sperner system $\mathcal{F}\subseteq \mathcal{P}(X)$ has cardinality at least $2^{(1+o(1))ck}$? \end{question}

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

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

Author(s): Allagan

\begin{question} Given $a,b\geq2$, what is the smallest integer $t\geq0$ such that $\chi_\ell(K_{a,b}+K_t)= \chi(K_{a,b}+K_t)$? \end{question}

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

Geometric Hales-Jewett Theorem ★★

Author(s): Por; Wood

\begin{conjecture} For all integers $k\geq1$ and $\ell\geq3$, there is an integer $f(k,\ell)$ such that for every set $P$ of at least $f(k,\ell)$ points in the plane, if each point in $P$ is assigned one of $k$ colours, then: \begin{itemize} \item $P$ contains $\ell$ collinear points, or \item $P$ contains a monochromatic line (that is, a maximal set of collinear points receiving the same colour) \end{itemize} \end{conjecture}

Keywords: Hales-Jewett Theorem; ramsey theory