Mikhail Moshkov Andrzej Skowron Zbigniew Suraj On Irreducible Descriptive Sets of Attributes for Information Systems. 21-30 2008 RSCTC http://dx.doi.org/10.1007/978-3-540-88425-5_3 conf/rsctc/2008 db/conf/rsctc/rsctc2008.html#MoshkovSS08