ABSTRACT
In Section 3.4.1 we introduced some basic graph-theoretic concepts. In this section we extend this material specializing to trees. A tree T = (V,E) is a connected undirected graph with no cycles. In particular, for any two u, v ∈ V there is a unique path between them, which we denote by uv. A vertex of T that has only one neighbor is called a leaf . A vertex of T that is not a leaf is called an inner vertex. An edge of T is inner if both of its ends are inner vertices, otherwise it is called terminal . A connected subgraph of T is called a subtree of T .
