
arXiv: 1901.03218
A graph $G$ is well-covered if all maximal independent sets of $G$ have the same cardinality. In 1992 Topp and Volkmann investigated the structure of well-covered graphs that have nontrivial factorizations with respect to some of the standard graph products. In particular, they showed that both factors of a well-covered direct product are also well-covered and proved that the direct product of two complete graphs (respectively, two cycles) is well-covered precisely when they have the same order (respectively, both have order 3 or 4). Furthermore, they proved that the direct product of two well-covered graphs with independence number one-half their order is well-covered. We initiate a characterization of nontrivial, connected well-covered graphs $G$ and $H$, whose independence numbers are strictly less than one-half their orders, such that their direct product $G \times H$ is well-covered. In particular, we show that in this case both $G$ and $H$ have girth 3 and we present several infinite families of such well-covered direct products. Moreover, we show that if $G$ is a factor of any well-covered direct product, then $G$ is a complete graph unless it is possible to create an isolated vertex by removing the closed neighborhood of some independent set of vertices in $G$.
05C69, 05C76, Graph operations (line graphs, products, etc.), Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), 05c69, Edge subsets with special properties (factorization, matching, partitioning, covering and packing, etc.), QA1-939, FOS: Mathematics, 05c76, Mathematics - Combinatorics, well-covered graph, direct product of graphs, isolatable vertex, Combinatorics (math.CO), Mathematics
05C69, 05C76, Graph operations (line graphs, products, etc.), Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), 05c69, Edge subsets with special properties (factorization, matching, partitioning, covering and packing, etc.), QA1-939, FOS: Mathematics, 05c76, Mathematics - Combinatorics, well-covered graph, direct product of graphs, isolatable vertex, Combinatorics (math.CO), Mathematics
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