Srinivasa R. Danda, Xiaolin Liu, Sreekrishna Madhwapathy, Anand Panyam, Naveed A. Sherwani, Ioannis G. Tollis: Optimal algorithms for planar over-the-cell routing problems. IEEE Trans. Comput. Aided Des. Integr. Circuits Syst. 15(11): 1365-1378 (1996)