A bound on the <Emphasis Type="Italic">k</Emphasis>-domination number of a graph

Let G be a graph with vertex set V(G), and let k ⩾ 1 be an integer. A subset D ⊆ V(G) is called a k-dominating set if every vertex υ ∈ V(G)-D has at least k neighbors in D. The k-domination number γ _k (G) of G is the minimum cardinality of a k-dominating set in G. If G is a graph with minimum degree δ(G) ⩾ k + 1, then we prove that

$ \gamma _{k + 1} (G) \leqslant \frac{{|V(G)| + \gamma _k (G)}} {2}. $ \gamma _{k + 1} (G) \leqslant \frac{{|V(G)| + \gamma _k (G)}} {2}.
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