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arXiv · 2602.09896

Eve-positional languages: putting order into Büchi automata

Olivier Idir
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Abstract

An $ω$-regular language is Eve-positional if, in all games with this language as objective, the existential player can play optimally without keeping any information from the previous moves. This notion plays a crucial role in verification, automata theory and synthesis. Casares and Ohlmann recently gave several characterisations of Eve-positionality of $ω$-regular languages. For this, they introduce the notion of $\varepsilon$-complete parity automaton and show (among other results) that an $ω$-regular language is Eve-positional if and only if it can be recognised by some $\varepsilon$-completion of a deterministic parity automaton. Colcombet and Idir built on their work, and obtained a more direct algebraic characterisation of Eve-positionality. We introduce a new formalism that characterises the Eve-positional languages, consisting of a restriction of non-deterministic Büchi automata. This allows us to complete a missing implication in Casares and Ohlmann's work. We then use this formalism to describe a determinization procedure for non-deterministic Büchi automata recognising such languages, with size blow-up at most factorial. We also show that this construction is state-wise optimal for languages over sufficiently complete alphabets.

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Olivier Idir. 2026-04-24. Eve-positional languages: putting order into Büchi automata. https://arxiv.org/abs/2602.09896

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