
doi: 10.7151/dmgt.2413
Summary: Perfect digraphs have been introduced in [\textit{S. D. Andres} and \textit{W. Hochstättler}, J. Graph Theory 79, No. 1, 21--29 (2015; Zbl 1312.05059)] as those digraphs where, for any induced subdigraph, the dichromatic number and the symmetric clique number are equal. Dually, we introduce a directed version of the clique covering number and define \(\alpha \)-perfect digraphs as those digraphs where, for any induced subdigraph, the clique covering number and the stability number are equal. It is easy to see that \(\alpha \)-perfect digraphs are the complements of perfect digraphs. A digraph is strictly perfect if it is perfect and \(\alpha \)-perfect. We generalise the Strong Perfect Graph Theorem and Lovász asymmetric version of the Weak Perfect Graph Theorem [\textit{L. Lovász}, J. Comb. Theory, Ser. B 13, 95--98 (1972; Zbl 0241.05107)] to the classes of perfect, \( \alpha \)-perfect and strictly perfect digraphs. Furthermore, we characterise strictly perfect digraphs by symmetric chords and non-chords in their directed cycles. As an example for a subclass of strictly perfect digraphs, we show that directed cographs are strictly perfect.
strong perfect graph theorem, Perfect graphs, dichromatic number, Directed graphs (digraphs), tournaments, filled odd hole, weak perfect graph theorem, filled odd antihole, strictly perfect digraph, acyclic set, Coloring of graphs and hypergraphs, Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), directed cograph, perfect graph, perfect digraph, \( \alpha \)-perfect digraph, clique-acyclic clique
strong perfect graph theorem, Perfect graphs, dichromatic number, Directed graphs (digraphs), tournaments, filled odd hole, weak perfect graph theorem, filled odd antihole, strictly perfect digraph, acyclic set, Coloring of graphs and hypergraphs, Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), directed cograph, perfect graph, perfect digraph, \( \alpha \)-perfect digraph, clique-acyclic clique
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