Rajab Ali Borzooei S. Khosravi Shoar Reza Ameri Some types of filters in MTL-algebras. 92-102 2012 187 Fuzzy Sets Syst. 1 https://doi.org/10.1016/j.fss.2011.09.001 db/journals/fss/fss187.html#BorzooeiSA12