Erik Rissanen Babak Sadighi Firozabadi Marek J. Sergot Discretionary Overriding of Access Control in the Privilege Calculus. 219-232 2004 conf/ifip1-7/2004 Formal Aspects in Security and Trust http://dx.doi.org/10.1007/0-387-24098-5_16 db/conf/ifip1-7/fast2004.html#RissanenFS04