Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques 12th International Workshop, APPROX 2009, and 13th International Workshop, RANDOM 2009, Berkeley, CA, USA, August 21-23, 2009. Proceedings - Dinur, Irit; Jansen, Klaus; Naor, Joseph; Rolim, José (Springer Berlin Heidelberg : Imprint: Springer, 2009)