Hussam Hamrawi Simon Coupland Type-2 Fuzzy Arithmetic using Alpha-planes. 606-611 2009 IFSA/EUSFLAT Conf. http://www.eusflat.org/proceedings/IFSA-EUSFLAT_2009/pdf/tema_0606.pdf conf/eusflat/2009 db/conf/eusflat/eusflat2009.html#HamrawiC09