On the existence of $3$- and $4$-kernels in digraphs

Sebastián González Hermosillo de la Maza, César Hernández-Cruz

Let $D=(V(D),A(D))$ be a digraph. A subset $S\subseteq V(D)$ is $k$-independent if the distance between every pair of vertices of $S$ is at least $k$, and it is $\ell$-absorben…