Harary, Frank. Structural models : an introduction to the theory of directed graphs / by Frank Harary, Robert Z. Norman and Dorwin Cartwright. - New York : Wiley, 1965. - ix, 415 p. : illu. ; 24 cm. Includes glossary and index. ISBN: 9780471351306 (hbk.) 047135130X (hbk.) Subjects--Topical Terms: Mathematical models. Dewey Class. No.: 511.5 / HAR/S