Markus Chimani Maria Kandyba Ivana Ljubic Petra Mutzel Obtaining Optimal k-Cardinality Trees Fast. 27-36 2008 ALENEX http://www.siam.org/proceedings/alenex/2008/alx08_03chimanim.pdf conf/alenex/2008 db/conf/alenex/alenex2008.html#ChimaniKLM08