Propositional dynamic logic of context-free programs and fixpoint logic with chop.

Martin Lange Rafal Somla Propositional dynamic logic of context-free programs and fixpoint logic with chop. 72-75 2006 100 Inf. Process. Lett. 2 http://dx.doi.org/10.1016/j.ipl.2006.04.019 db/journals/ipl/ipl100.html#LangeS06