Annalisa Bossi Riccardo Focardi Carla Piazza Sabina Rossi Refinement Operators and Information Flow Security. 44-53 2003 conf/sefm/2003 SEFM http://csdl.computer.org/comp/proceedings/sefm/2003/1949/00/19490044abs.htm db/conf/sefm/sefm2003.html#BossiFPR03