Distance-two labelings of digraphs

G. J. Chang, J. -J. Chen, D. Kuo +1

For positive integers $j\ge k$, an $L(j,k)$-labeling of a digraph $D$ is a function $f$ from $V(D)$ into the set of nonnegative integers such that $|f(x)-f(y)|\ge j$ if $x$ is adja…