Buekenhout, F. (Ed.). Handbook of Incidence Geometry: Building and Foundations. Amsterdam, Netherlands: North-Holland, 1995.Colbourn, C. J. and Dinitz, J. H. (Eds.). CRC Handbook of Combinatorial Designs. Boca Raton, FL: CRC Press, 1996.Mallows, C. L. and Sloane, N. J. A. "Two-Graphs, Switching Classes, and Euler Graphs are Equal in Number." SIAM J. Appl. Math.28, 876-880, 1975.Robinson, R. W. "Enumeration of Euler Graphs." In Proof Techniques in Graph Theory (Ed. F. Harary). New York: Academic Press, pp. 147-153, 1969.Seshu, S. and Reed, M. B. Linear Graphs and Electrical Networks. Reading, MA: Addison-Wesley, 1961.Sloane, N. J. A. Sequences A002854/M0846 and A189771 in "The On-Line Encyclopedia of Integer Sequences."