"Characterizing fuzzy modal semantics by fuzzy multimodal systems with crisp accessibility relations" (2009) Bou, F.; Esteva, F.; Godo, L.; Rodríguez, R. Joint 2009 International Fuzzy Systems Association World Congress, IFSA 2009 and 2009 European Society of Fuzzy Logic and Technology Conference, EUSFLAT 2009:1541-1546