Siberian Mathematical Journal, Vol. 35, No. 3, 1994 DOMINATING SETS AND HAMILTONICITY Summary: Siberian Mathematical Journal, Vol. 35, No. 3, 1994 DOMINATING SETS AND HAMILTONICITY IN K 1;3 ­FREE GRAPHS y) A. A. Ageev UDC 519.17 1. Introduction. An undirected graph is called K 1;3 ­free, if it contains no induced subgraph isomorphic to the complete bipartite graph K 1;3 . The class of K 1;3 ­free graphs includes all the line graphs and is well studied in many aspects. For instance, it is known that, for K 1;3 ­free graphs, the strong Berge conjecture holds [1], and certain problems that are NP­complete in the general setting are polynomially solvable for them [2, 3]. Since the middle of the 70s the articles have begun to appear that are devoted to study of conditions sufficient for hamiltonicity of a K 1;3 ­free graph (see Section 3 of the newest survey by Gould [4]). It is the following conjecture extending Thomassen's conjecture for line graphs [5] that became widely known. Conjecture [6]. Every 4­connected K 1;3 ­free graph is Hamiltonian. It is known that the Hamiltonian cycle problem is NP­complete for 3­connected cubic planar graphs [7]. Plummer and Pulleyblank [8] showed that there exist infinitely many non­Hamiltonian 3­connected cubic graphs that, moreover, possess no dominating cycles. It is easy to observe that the replacement of vertices with triangles transforms a 3­connected cubic graph into a 3­connected K 1;3 ­free graph; moreover, the former is Hamiltonian if and only if such is the latter. Consequently, the above­cited assertions for 3­connected cubic graphs are also valid for the 3­connected K 1;3 ­free graphs. Collections: Mathematics