Eliminating the storage tape in reachability constructions

A discrete pushdown timed automaton is a pushdown machine with integer-valued clocks. It has been shown recently that the binary reachability of a discrete pushdown timed automaton can be accepted by a two-tape pushdown acceptor with reversal-bounded counters. We improve this result by showing that the stack can be eliminated from the acceptor, i.e., the binary reachability can be accepted by a two-tape finite-state acceptor with reversal-bounded counters. We also obtain similar results for other machine models. Our results can be used to verify certain properties concerning these machines that were not verifiable before using previous techniques. For example, we are able to formulate a subset of Presburger LTL that is decidable for satisfiability checking with respect to these machines. We also discuss the “boundedness problem” for reachability sets. Finally, we explain how the storage tape elimination technique can be applied to machines with real-valued clocks.

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