Abstract. We present an LTL model checker whose code has been completely verified using the Isabelle theorem prover. The checker consists of over 4000 lines of ML code. The code is produced using recent Isabelle technology called the Refinement Framework, which allows us to split its correctness proof into (1) the proof of an abstract version of the checker, consisting of a few hundred lines of "formalized pseudocode", and (2) a verified refinement step in which mathematical sets and other abstract structures are replaced by implementations of efficient structures like red-black trees and functional arrays. This leads to a checker that, while still slower than unverified checkers, can already be used as a trusted reference implementation against which advanced implementations can be tested. We report on the structure of the checker, the development process, and some experiments on standard benchmarks.
Abstract. We present the implementation in Isabelle/HOL of a translation of LTL formulae into Büchi automata. In automaton-based model checking, systems are modelled as transition systems, and correctness properties stated as formulae of temporal logic are translated into corresponding automata. An LTL formula is represented by a (generalised) Büchi automaton that accepts precisely those behaviours allowed by the formula. The model checking problem is then reduced to checking language inclusion between the two automata. The automaton construction is thus an essential component of an LTL model checking algorithm. We implemented a standard translation algorithm due to Gerth et al. The correctness and termination of our implementation are proven in Isabelle/HOL, and executable code is generated using the Isabelle/HOL code generator.
OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Abstract. In applications of automata theory, one is interested in reductions in the size of automata that preserve the recognised language. For Büchi automata, two optimisations have been proposed: bisimulation reduction, which computes equivalence classes of states and collapses them, and α-balls reduction, which collapses strongly connected components (SCCs) of an automaton that only contain one single letter as edge label. In this paper, we present a formalisation of these algorithms in Isabelle/HOL, providing a formally verified implementation.
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