Maciej Wygralak Cardinalities of fuzzy sets with triangular norms. 691-696 2003 EUSFLAT Conf. http://www.eusflat.org/publications/proceedings/EUSFLAT_2003/papers/1Wygralak.pdf conf/eusflat/2003 db/conf/eusflat/eusflat2003.html#Wygralak03