Classical realizability and arithmetical formulæ

International audienceIn this paper we treat the specification problem in Krivine classical realizability, in the case of arithmetical formulæ. In the continuity of previous works from Miquel and the first author, we characterize the universal realizers of a formula as being the winning strategies for a game (defined according to the formula). In the first sections we recall the definition of classical realizability, as well as a few technical results. In Section 5, we introduce in more details the specification problem and the intuition of the game-theoretic point of view we adopt later. We first present a game $\G^{1}$, that we prove to be adequate and complete if the language contains no instructions `quote', using interaction constants to do substitution over execution threads. We then show that as soon as the language contain `quote', the game is no more complete, and present a second game $\G^{2}$ that is both adequate and complete in the general case. In the last Section, we draw attention to a model-theoretic point of view and use our specification result to show that arithmetical formulæ are absolute for realizability models