@BOOK { Rsds2346,
author = {Polkowski, Lech T.}, 
title = {Rough Sets: Mathematical Foundations}, 
series =  = {Advances in Soft Computing}, 
publisher = {Springer-Verlag}, 
address = {Heidelberg - Berlin, Germany}, 
year = 2002, 
url = {http://www.springer.de}, 
isbn = {3-7908-1510-1}, 
keywords = {fuzzy set theory, fuzzy sets, mathematical foundations, rough sets, rough sets theory (RST), }, 
}