 For more on epistemic interaction principles, the principles .2, .3, .3.2. and .4, and relations to so-called conditional beliefs, see Aucher (2014). For an introduction to conditional beliefs and relations to several other types of knowledge from the philosophical literature, see Baltag and Smets (2008). The latter also includes discussion concerning the interdefinability of various notions, as does Halpern, Samet, and Segev (2009) for knowledge and (non-conditional) belief.