Iranian Mathematical Society (IMS) Bulletin of the Iranian Mathematical Society 1017-060X 38 1 2012 04 01 On Heyting algebras and dual BCK-algebras159 168 en Y. Yon Mokwon University K. H. Kim Chungju National University 2009 04 30 Heyting semilattice Heyting algebra dual $BCK$-algebra