2 problems

Let $G$ be a graph and let $A$ be a subset of the vertices of $G$. An $A$-path is a path in $G$ whose two endpoints belong to $A$. For subsets $X$ of vertices of $G$ and integers…

Fejes Tóth's hexagonal density conjecture. For any $\mu\in(\sqrt{3}-1,1)$ and any $\mu$-arrangement $\mathcal{F}$ in $\mathbb{R}^2$,