ABSTRACT

Directed graphs have already been introduced in the Chapter 1. IfG is a digraph and u, v ∈ V (G), we write u −→ v to indicate that the edge uv is directed from u to v. The in-edges at v are the edges of the form (u, v). The in-degree of v is d−(v), the number of in-edges. Similarly the out-edges at u are all edges of the form (u, v) and the out-degree d+(u) is the number of out-edges at u. The degree of u is

DEG(u) = d+(u) + d−(u).