3 problems

Let $n$ be the order of a bipartite biconnected digraph, let $r=\operatorname{rad}^+\geq 4$, and let $D_{n,r,s}$ be the specified digraph family. Let…

Let a biconnected digraph mean a strong digraph, and let its order be $n$ and its outradius be $r$. For $r\geq 3$ and $n\geq 2r$, let $D_{n,r,s}$ denote the specified family of ext…

Dutton–Medidi–Brigham converse conjecture. There exists a radially maximal graph with radius $r$ and diameter $d$.