1. Cattaneo, G.: Rough Set Theory II. The Approximation Space Approach. with Applications to Roughness and Fuzzy Set Theory.
http://www.fislab.disco.unimib.it/dl.php?file=/lib/exe/fetch.php/book/
2. Cattaneo, G., Ciucci, D.: Lattices with Interior and Closure Operators and Abstract Approximation Spaces. Transactions on Rough Sets X. Springer (2009)
3. Crown, G.D., Harding, J., Janowitz, M.F.: Boolean products of lattices. Order 13, 175–205 (1996)
4. Gabbay, D.M.: Labelled Deductive Systems. Oxford University Press (1997)
5. Greco, S., Matarazzo, B., Slowinski, R.: Rough sets theory for multi-criteria decision analysis. Euro. J. Op. Res. 129(1), 1–47 (2001)