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Discussiones Mathematicae Graph Theory
Article . 1999 . Peer-reviewed
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Distance perfectness of graphs

Authors: Andrzej Włoch;

Distance perfectness of graphs

Abstract

The author introduces a new generalization of perfect graphs. It turns out that the analogue of the weak perfect graph theorem is not true for this generalization. A subset \(Q\) of the vertex set \(V\) of a graph \(G\) is a \(k\)-distance clique in \(G\) if \(d_G(x,y)\leq k\) for any \(x,y\in Q\) and \(\langle Q\rangle_G\), the subgraph of \(G\) induced on \(Q\), is connected. A subset \(S\) of \(V\) is a \(k\)-stable transversal of \(G\) if \(|S\cap Q|= 1\) for each maximal \(k\)-distance clique \(Q\) of \(G\). A subset \(S\) of \(V\) such that \(d_G(x,y)> k\) for every \(x,y\in S\) is called a \(k\)-distance stable set in \(G\). The \(k\)-distance chromatic number \(\chi_k(G)\) is the smallest cardinality of a partition of \(V\) into \(k\)-distance stable sets. The minimum number of \(k\)-distance cliques which cover \(V\) is \(\theta_k(G)\). The cardinalities of a maximum \(k\)-distance clique and a maximum \(k\)-distance stable set are denoted by \(\omega_k(G)\) and \(\alpha_k(G)\). By \(H\leq G\) is meant that \(H\) is an induced subgraph of \(G\). Let \({\mathcal P}_{\chi_k}= \{G\mid \chi_k(H)= \omega_k(H)\) for each \(H\leq G\}\), \({\mathcal P}_{\alpha_k}= \{G\mid \alpha_k(H)= \theta_k(H)\) for each \(H\leq G\}\), and \({\mathcal P}_{kS}= \{G\mid H\) has a \(k\)-stable transversal for each \(H\leq G\}\). These classes respectively generalize the classes of \(\chi\)-perfect, \(\alpha\)-perfect and strongly perfect graphs. After considering several relations between these classes and some special cases like \(G\) being a tree, the author eventually proves: (1) \({\mathcal P}_{kS}\subset{\mathcal P}_{\chi_k}\) if and only if \(k=1\). (2) \({\mathcal P}_{kS}\subset{\mathcal P}_{\alpha_k}\) if and only if \(k=1\). (3) \({\mathcal P}_{\alpha_k}={\mathcal P}_{\chi_k}\) if and only if \(k=1\). Note that \(k=1\) corresponds to the respective ordinary perfectness classes.

Keywords

Perfect graphs, strongly perfect graphs, \(k\)-distance clique, partition, perfectness, Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), \(k\)-stable transversal, Isomorphism problems in graph theory (reconstruction conjecture, etc.) and homomorphisms (subgraph embedding, etc.), Structural characterization of families of graphs, perfect graphs, \(k\)-distance chromatic number

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
2
Average
Average
Average
Published in a Diamond OA journal