Valentina Cacchiani Alberto Caprara Matteo Fischetti Robustness in Train Timetabling. 171-174 2009 CTW http://www.lix.polytechnique.fr/ctw09/ctw09-proceedings.pdf#page=183 conf/colognetwente/2009 db/conf/colognetwente/colognetwente2009.html#CacchianiCF09