Feng-xiao Wang Lu Chen On (Alpha, Beta) Fuzzy Subalgebras of BCH-Algebras. 604-607 2008 FSKD (3) http://dx.doi.org/10.1109/FSKD.2008.72 conf/fskd/2008-3 db/conf/fskd/fskd2008-3.html#WangC08