Substituting strict equivalents

摘要

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+square SP is strictly contained between S1+SP and S3' (2016, J. Logic Comput., 26, 1780).