Alexandru Baltag A Coalgebraic Semantics for Epistemic Programs. 2003 82 Electr. Notes Theor. Comput. Sci. 1 http://www1.elsevier.com/gej-ng/31/29/23/133/49/show/Products/notes/index.htt#003 db/journals/entcs/entcs82.html#Baltag03