George Christodoulou Elias Koutsoupias Paul G. Spirakis On the Performance of Approximate Equilibria in Congestion Games. 251-262 2009 ESA http://dx.doi.org/10.1007/978-3-642-04128-0_22 conf/esa/2009 db/conf/esa/esa2009.html#ChristodoulouKS09