 The product formula_2 is a four-dimensional hypercube graph; it has 16 vertices, and any single vertex can only dominate itself and four neighbors, so three vertices could only dominate 15 of the 16 vertices.Therefore, at least four vertices are required to dominate the entire graph, the bound given by Vizing's conjecture.It is possible for the domination number of a product to be much larger than the bound given by Vizing's conjecture.