“…These theorems are later generalized to non-decreasing cost functions (Rinnooy Kan et al, 1975). Exact methods rely either on 0740-817X © 2001 "lIE" branch and bound (Schwimer, 1972;Rinnooy Kan et al, 1975;Fisher, 1976;Picard and Queyranne, 1978;Sen et al, 1983;Potts and van Wassenhove, 1985;Sen and Borah, 1991;Szwarc and Mukhopadhyay, 1996) or on dynamic programming (Srinivasan, 1971;Lawler, 1977;Schrage and Baker, 1978;Potts andvan Wassenhove, 1982, 1987).…”