Covering the edges of digraphs in $\mathscr{D}(3,3)$ and   $\mathscr{D}(4,4)$ with directed cuts
  For nonnegative integers $k$ and $l$, let $\mathscr{D}(k,l)$ denote the family of digraphs in which every vertex has either indegree at most $k$ or outdegree at most $l$. In this paper we prove that the edges of every digraph in $\mathscr{D}(3,3)$ and $\mathscr{D}(4,4)$ can be covered by at most five directed cuts and present an example in $\mathscr{D}(3,3)$ showing that this result is best possible. 
Yandong Bai, Binlong Li, Shenggui Zhang
math.CO