Formal language constrained reachability and model checking propositional dynamic logics
RP'11 Proceedings of the 5th international conference on Reachability problems
Propositional dynamic logic with recursive programs
FOSSACS'06 Proceedings of the 9th European joint conference on Foundations of Software Science and Computation Structures
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We continue the ongoing investigation of decidability and undecidability of nonregular extensions of propositional dynamic logic (PDL), by proving two results. The first strengthens the undecidability result of Harel and Singerman regarding one-letter Fibonacci-like extensions, by showing undecidability for a more general class of exponentially growing sequences. The second strengthens the decidability result of Harel and Raz for languages accepted by simple-minded pushdown automata, by showing that the important thing for decidability is that the stack behavior depends only on the input symbol.