Edward P. K. Tsang Timothy Gosling Botond Virginas Christos Voudouris Gilbert Owusu Wudong Liu Retractable contract network for empowerment in workforce scheduling. 25-44 2008 4 Multiagent and Grid Systems 1 http://iospress.metapress.com/content/k031614j56527565/ db/journals/mags/mags4.html#TsangGVVOL08