Petr Kovár

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It was proved by Fronček, Jerebic, Klavžar, and Kovář that if a complete bi-partite graph K n,n with a perfect matching removed can be covered by k bicliques, then n ≤ k k 2. We give a slightly simplified proof and we show that the result is tight. Moreover we use the result to prove analogous bounds for coverings of some other classes of graphs by(More)
Let G(V, E) be a graph and λ be a bijection from the set V ∪ E to the set of the first |V | + |E| natural numbers. The weight of a vertex is the sum of its label and the labels of all adjacent edges. We say λ is a vertex magic total (VMT) labeling of G if the weight of each vertex is constant. We say λ is an (s, d)-vertex antimagic total (VAT) labeling if(More)
Let G = (V, E) be a graph on n vertices. A bijection f : V → {1, 2,. .. , n} is called a distance magic labeling of G if there exists an integer k such that u∈N (v) f (u) = k for all v ∈ V , where N(v) is the set of all vertices adjacent to v. The constant k is the magic constant of f and any graph which admits a distance magic labeling is a distance magic(More)