Antonio Frangioni Andrea Lodi Giovanni Rinaldi Optimizing over Semimetric Polytopes. 431-443 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3064&spage=431 2004 conf/ipco/2004 IPCO db/conf/ipco/ipco2004.html#FrangioniLR04