Meinolf Sellmann Kyriakos Zervoudakis Panagiotis Stamatopoulos Torsten Fahle Crew Assignment via Constraint Programming: Integrating Column Generation and Heuristic Tree Search. 207-225 2002 115 Annals OR 1-4 http://dx.doi.org/10.1023/A:1021105422248 db/journals/anor/anor115.html#SellmannZSF02