1. C. Berge and A. Ghouilla-Houri, “Programming, Games and Transportation Networks”, John Wiley & Sons, 1965.
2. W. Dai, T. Asano and E. Kuh, “Routing Region Definition and Ordering Scheme for Building Block Layout”, IEEE Trans. on CAD, vol CAD-4, no 3, pp. 189–197, July 1985.
3. E. Dijkstra, “A Note on Two Problems in Connection with Graphs”, Numer. Math., vol. 1, pp 267–271, 1959.
4. D. Harrison et all, “Data Management and Graphics Editing in the Berkeley Design Environment”, Proc. IEEE ICCAD Conf, Santa Clara, 1986.
5. R. Karp, “Reducibility among Combinatorial Problems”, Proc. Complexity of Computer Computations, pp. 85–104, Plenum Press, New york, 1972.