Chris Cornelis Martine De Cock Anna Maria Radzikowska Vaguely Quantified Rough Sets. 87-94 2007 conf/rsfdgrc/2007 RSFDGrC http://dx.doi.org/10.1007/978-3-540-72530-5_10 db/conf/rsfdgrc/rsfdgrc2007.html#CornelisCR07