Let n be a positive integer and let Gn be the set of all simple graphs on n vertices. For each vertex v of a graph in Gn, let k(v) be the maximal cardinality of an independent set of neighbours of v. Determine maxG∈GnΣv∈V(G)k(v) and the graphs in Gn that achieve this value. graphgraph theoryMaximalVerticescombinatorics