Yoshiyuki Karuno Hiroshi Nagamochi An approximability result of the multi-vehicle scheduling problem on a path with release and handling times. 267-280 2004 312 Theor. Comput. Sci. 2-3 http://dx.doi.org/10.1016/j.tcs.2003.09.010 db/journals/tcs/tcs312.html#KarunoN04