Alexandru Baltag Sonja Smets Conditional Doxastic Models: A Qualitative Approach to Dynamic Belief Revision. 5-21 2006 165 Electr. Notes Theor. Comput. Sci. http://dx.doi.org/10.1016/j.entcs.2006.05.034 db/journals/entcs/entcs165.html#BaltagS06a