Formalized soundness and completeness of epistemic and public announcement logic

I strengthen the foundations of epistemic logic by formalizing the family of normal modal logics in the proof assistant Isabelle/HOL. I define an abstract canonical model over any set of axioms and formalize completeness-via-canonicity: when the canonical model for the chosen axioms belongs to a certain class of frames, strong completeness over that class follows immediately. I instantiate the result with logics based on various epistemic principles to obtain completeness results for systems from K to S5. I then move to a family of public announcement logics (PAL) and prove abstract results for strong soundness and completeness. I lift the completeness results from epistemic logic to the setting with public announcements in a modular way. This work formulates the completeness-via-canonicity technique as a proper theorem and demonstrates its applicability. Additionally, it succinctly formalizes the requirements for lifting completeness from bare epistemic logic to the addition of public announcements.