Epistemic Actions and Ontic Actions: A Unified Logical Framework

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We present a reasoning about actions framework based on a sum of epistemic logic S5 and propositional dynamic logic PDL together with a ‘no forgetting’ principle, also called perfect recall. We show that in our framework an action may be decomposed into a purely ontic action followed by a purely epistemic action. We also show that the latter is completely definable in terms of simple observations, i.e., ‘test that’ actions and that they are equivalent to public announcements of public announcement logic PAL as studied by Plaza, van Benthem and others. Finally, since these actions respect ‘no learning’ principle we show that a unified reduction method based on regression, as studied by Reiter, applies.