Douglas E. Carroll Adam Meyerson Brian Tagiku Approximations for Aligned Coloring and Spillage Minimization in Interval and Chordal Graphs. 29-41 2009 APPROX-RANDOM http://dx.doi.org/10.1007/978-3-642-03685-9_3 conf/approx/2009 db/conf/approx/approx2009.html#CarrollMT09