
arXiv: 1108.3756
A set S is independent in a graph G if no two vertices from S are adjacent. The independence number alpha(G) is the cardinality of a maximum independent set, while mu(G) is the size of a maximum matching in G. If alpha(G)+mu(G)=|V|, then G=(V,E) is called a Konig-Egervary graph. The number d_{c}(G)=max{|A|-|N(A)|} is called the critical difference of G (Zhang, 1990). By core(G) (corona(G)) we denote the intersection (union, respectively) of all maximum independent sets, while by ker(G) we mean the intersection of all critical independent sets. A connected graph having only one cycle is called unicyclic. It is known that ker(G) is a subset of core(G) for every graph G, while the equality is true for bipartite graphs (Levit and Mandrescu, 2011). For Konig-Egervary unicyclic graphs, the difference |core(G)|-|ker(G)| may equal any non-negative integer. In this paper we prove that if G is a non-Konig-Egervary unicyclic graph, then: (i) ker(G)= core(G) and (ii) |corona(G)|+|core(G)|=2*alpha(G)+1. Pay attention that |corona(G)|+|core(G)|=2*alpha(G) holds for every Konig-Egervary graph.
8 pages, 5 figures
FOS: Computer and information sciences, Extremal problems in graph theory, critical set, Discrete Mathematics (cs.DM), core, G.2.2, maximum independent set, Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), 05C69, 05C38 (Primary) 05C70, 05C05(Secondary), FOS: Mathematics, Mathematics - Combinatorics, König-Egerváry graph, Combinatorics (math.CO), Paths and cycles, corona, unicyclic graph, Computer Science - Discrete Mathematics
FOS: Computer and information sciences, Extremal problems in graph theory, critical set, Discrete Mathematics (cs.DM), core, G.2.2, maximum independent set, Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), 05C69, 05C38 (Primary) 05C70, 05C05(Secondary), FOS: Mathematics, Mathematics - Combinatorics, König-Egerváry graph, Combinatorics (math.CO), Paths and cycles, corona, unicyclic graph, Computer Science - Discrete Mathematics
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