On the hull sets and hull number of the cartesian product of graphs

For a connected graph G, the convex hull of a subset C of image is defined as the smallest convex set in G containing C. A subset C of image is a hull set in G if the convex hull of C is image. The cardinality of a minimum hull set in G is called the hull number of G. Chartrand, Harary and Zhang (2000) presented the hull number of the Cartesian product of a nontrivial connected graph and image. In this paper, we give the hull number of the Cartesian product of any two connected graphs.