Two Graphs which contain the same number of Vertices connected in the same way are said to be isomorphic. Formally, two graphs and with Vertices are said to be isomorphic if there is a Permutation of such that is in the set of Edges Iff is in the set of Edges .
Chartrand, G. ``Isomorphic Graphs.'' §2.2 in Introductory Graph Theory. New York: Dover, pp. 32-40, 1985.