Tetsuo Asano Naoki Katoh Kazuhiro Kawashima A New Approximation Algorithm for the Capacitated Vehicle Routing Problem on a Tree. 213-231 2001 5 J. Comb. Optim. 2 db/journals/jco/jco5.html#AsanoKK01 http://dx.doi.org/10.1023/A:1011461300596