User:Oliver drishila/sandbox/L(h,k) colouring

L(h,k) colouring Given a graph G = (V, E) and two nonnegative integers h and k, an L(h, k)-labelling is an assignment of nonnegative integers to the nodes of G such that adjacent nodes are labelled using colors at least h apart, and nodes having a common neighbour are labelled using colors at least k apart. The aim of the L(h, k)-labelling problem is to minimize the span σh,k(G), i.e. the difference between the largest and the smallest used colors. The minimum span over all possible labelling functions is denoted by λ_h,k(G) and is called λ_h,k-number of G.