Richard M. Karp. "Reducibility Among Combinatorial Problems". In: Raymond E. Miller, James W. Thatcher (Eds.): Proceedings of a symposium on the Complexity of Computer Computations, held March 20-22, 1972, at the IBM Thomas J. Watson Research Center, Yorktown Heights, New York. Plenum Press, New York 1972 (blz. 85-103)