Alon Efrat Frank Hoffmann Christian Knauer Klaus Kriegel Günter Rote Carola Wenk Covering with Ellipses. 145-160 2003 38 Algorithmica 1 http://dx.doi.org/10.1007/s00453-003-1047-0 db/journals/algorithmica/algorithmica38.html#EfratHKKRW03