José Miró-Julià José Miró Well-Behaviored Operations for Approximate Sets. 45-51 1998 conf/rsctc/1998 Rough Sets and Current Trends in Computing http://link.springer.de/link/service/series/0558/bibs/1424/14240045.htm db/conf/rsctc/rsctc1998.html#Miro-JuliaM98