@techreport{GroetschelHillerTuchscherer2007, author = {Martin Gr{\"o}tschel and Benjamin Hiller and Andreas Tuchscherer}, title = {Combinatorial Online Optimization: Elevators \& Yellow Angels}, institution = {ZIB}, address = {Takustr. 7, 14195 Berlin}, number = {07-36}, language = {eng}, year = {2007} }