Mariangiola Dezani-Ciancaglini Furio Honsell Fabio Alessi A complete characterization of complete intersection-type preorders. 120-147 2003 4 ACM Trans. Comput. Log. 1 http://doi.acm.org/10.1145/601775.601780 db/journals/tocl/tocl4.html#Dezani-CiancagliniHA03