Kai Engelhardt Towards a refinement theory that supports reasoning about knowledge and time for multiple agents. 2002 70 Electr. Notes Theor. Comput. Sci. 3 http://www.elsevier.com/gej-ng/31/29/23/125/48/show/Products/notes/index.htt#014 db/journals/entcs/entcs70.html#Engelhardt02