COMPLETENESS FOR VARIOUS LOGICS OF ESSENCE AND ACCIDENT
Christopher Steinsvold · 2008
In a paper by Marcos (2005, this bulletin) logics of essence and accident (LEA) were presented with a completeness proof for the minimal logic, KEA, corresponding to the modal logic K. Using a dierent canonical approach, we establish completeness results for various logics. We answer two questions from that paper (an open question and a conjecture (in the armative)), by giving completeness proofs for the LEA of the modal logics K4 and T. Moreover, we show S4EA = K4EA, and KTEA = KEA. Also, there is a sentence of the language whose validity corresponds to a frame being weakly connected; this yields completeness for S4.3EA.