by Gabriel R. Bitran and Thomas L. Magnanti."8-189-78" "Several results from this paper were presented in less general form at the National ORSA/TIMS meeting, Chicago, May 1975." "This paper is a revision of core discussion paper #7716, June 1977."Bibliography: p. 54-58.Supported in part by the U.S. Army Research Office contract no. DAAG29-76-C-0064 Supported in part by the Office of Naval Research contract. N00014-75-C-0556