Some Properties of Graphs with Multiple Edges

Abstract

In this paper we consider undirected graphs, with no edges joining a vertex to itself, but with possibly several edges joining pairs of vertices. The first part of the paper deals with the question of characterizing those sets of non-negative integers d 1 d 2 . . . , d n and { c ij }, 1 ≤ i < j ≤ n , such that there exists a graph G with n vertices whose valences (degrees) are the numbers d i , and with the additional property that the number of edges joining i and j is at most c ij . This problem has been studied extensively, in the general case (1, 2, 9, 11), in the case where the graph is bipartite (3, 5, 7, 10), and in the case where the C ij are all 1 (6).