Alper Atamtürk George L. Nemhauser Martin W. P. Savelsbergh Valid Inequalities for Problems with Additive Variable Upper Bounds. 60-72 1999 conf/ipco/1999 IPCO http://link.springer.de/link/service/series/0558/bibs/1610/16100060.htm db/conf/ipco/ipco1999.html#AtamturkNS99