Atomi in klični separatorji v grafovskih produktih

Predstavljeni so vsi minimalni klični separatorji za vse štiri standardne produkte: kartezičnega, krepkega, leksikografskega in direktnega. Maksimalne atome natančno opišemo le za prve tri prej omenjene standardne produkte. V direktnem produktu maksimalne atome opišemo le delno. Tipična situacija za standardni grafovski produkt je, da ne vsebuje kličnih separatorjev in je posledično ves produkt maksimalni atom.We describe in the present work all minimal clique separators of the four standard products - Cartesian, strong, direct, and lexicographic - as well as all maximal atoms of the Cartesian, strong and lexicographic product, while we only partially describe maximal atoms of direct products. Typically, a product has no clique separator and so the product is a maximal atom

Some Steiner concepts on lexicographic products of graphs

The smallest tree that contains all vertices of a subset ▫$W$▫ of ▫$V(G)$▫ is called a Steiner tree. The number of edges of such a tree is the Steiner distance of ▫$W$▫ and union of all Steiner trees of ▫$W$▫ form a Steiner interval. Both of them are described for the lexicographic product in the present work. We also give a complete answer for the following invariants with respect to the Steiner convexity: the Steiner number, the rank, the hull number, and the Carathéodory number, and a partial answer for the Radon number. At the end we locate and repair a small mistake from [J. Cáceres, C. Hernando, M. Mora, I. M. Pelayo, M. L. Puertas, On the geodetic and the hull numbers in strong product graphs, Comput. Math. Appl. 60 (2010) 3020--3031]