1. On hearing the shape of a drum
2. Cospectral Graphs and Digraphs
3. and in Selected Topics in Graph Theory, and Eds., Academic, New York, 1978.
4. For contributions of A. T. Balaban, M. L. Ellzey, Jr., I. Gutman, E. Heilbronner, W. C. Herndon, H. Hosoya, Y. Jiang, M. Randi?, N. Trinajsti?, Q. E. Zhang, T. ?ivkovi?, and others in the chemical literature consult Chemical Graph Theory, CRC Press, Boca Raton, Florida, 1983, Vol. 1, Chap. 7.