1. Simple heuristics for the vehicle routing problem with soft time windows;Balakrishnan;Journal of the Operational Research Society,1993
2. A branch-and-cut procedure for the vehicle routing problem with time windows;Bard;Transportation Science,2002
3. H.I. Calvete, C. Galé, M.J. Oliveros, B. Sánchez-Valverde, Vehicle routing problems with soft time windows: An optimization based approach, in: M.C. López de Silanes et al. (Eds.), Proceedings of VIII Journées Zaragoza-Pau de Mathématiques Appliquées et Statistiques, vol. 31, Monografı´as del Seminario Matemático Garcı´a Galdeano, Univ. de Zaragoza, 2004, pp. 295–304.
4. Multiobjective Decision Making, Theory and Methodology;Chankong,1983