Substituting strict equivalents
David B. Martens · Journal of Logic and Computation · 2019
Abstract I discuss certain principles for substituting strictly equivalent propositions and provide alternative axiomatizations of some standard modal systems and proofs of containment relations among some systems that have the principles, including partial proof of Steffen Lewitzka’s ‘conjecture’ that ‘S1+$\Box $SP is strictly contained between S1+SP and S3’ (2016, J. Logic Comput., 26, 1780).