Takuro Fukunaga Magnús M. Halldórsson Hiroshi Nagamochi "Rent-or-Buy" Scheduling and Cost Coloring Problems. 84-95 2007 conf/fsttcs/2007 FSTTCS http://dx.doi.org/10.1007/978-3-540-77050-3_7 db/conf/fsttcs/fsttcs2007.html#FukunagaHN07