 In particular, one fundamental theme are syntactic perspectives on game-theoretic reasoning. Samples of a proof-theoretic style of analysis for play can be found in de Bruin (2005). More concretely, Zvesper (2010) analyzes classical results in epistemic game theory, (cf. Tan &amp; Werlang 1988; Aumann 1999), in terms of abstract modalities for belief and optimality, showing how a few simple proof rules from modal μ-calculus can capture the essence of famous results in epistemic game theory. Proof-theoretic aspects of logic have so far been overshadowed by semantic analyses, although this situation is changing slowly (Artemov 2014; Kaneko 2002; Kaneko &amp; Suzuki 2003). Model-based reasoning provides abstract semantic perspectives on games that can aid conceptual clarification, and the discovery of general laws. But it might turn out to be proof theory that governs the concrete reasoning used in the semantics, and that may be able to guide the context of justification in establishing general facts about games.