Jan Rothe Dragan Masulovic Towards Weak Bisimulation For Coalgebras. 2002 68 Electr. Notes Theor. Comput. Sci. 1 http://www.elsevier.com/gej-ng/31/29/23/121/50/show/Products/notes/index.htt#004 db/journals/entcs/entcs68.html#RotheM02