On Groups and Graphs
Chong-Yun Chao · Transactions of the American Mathematical Society · 1965
By a graph X we mean a finite set V(X), called the vertices of X, together with a set E(X), called the edges of X, consisting of unordered pairs of distinct elements of V(X).We shall indicate the unordered pairs by brackets.Two graphs X and Y are said to be isomorphic, denoted by X cz Y, if there is a one-to-one