Roderich Groß Marco Dorigo Cooperative Transport of Objects of Different Shapes and Sizes. 106-117 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3172&spage=106 2004 conf/antsw/2004 ANTS Workshop db/conf/antsw/antsw2004.html#GrossD04