Generalizing Propositional Dynamic Logic

A new semantics of Propositional Dynamic Logic (PDL) is given in terms of predicate transformers: Instead of associating the standard state transformer with each program, we model programs by operations on sets of states, operations which map postconditions to weakest liberal preconditions. This yields a logic more general than PDL since new program operations such as angelic choice become expressible. Three issues will be discussed: axiomatization, extension of the framework to total correctness reasoning and the relation to the -calculus.