Ricardo Oscar Rodríguez Francesc Esteva Pere Garcia Lluis Godo On implicative closure operators in approximate reasoning. 159-184 2003 33 Int. J. Approx. Reasoning 2 http://dx.doi.org/10.1016/S0888-613X(03)00016-1 db/journals/ijar/ijar33.html#RodriguezEGG03