vertex has outdegree at most 1. A functional graph is a special case of a pseudoforest in which every vertex has outdegree exactly 1. By Brooks' theorem, any graph G other than a clique or an odd cycle has chromatic number at most Δ(G), and by Vizing's theorem any graph has chromatic index at most Δ(G) + 1. A k-degenerate graph is a graph in which each subgraph has a vertex of degree at most k. See also Indegree, outdegree for digraphs Degree distribution Degree sequence for bipartite graphs Notes References . . . . Graph theory