A Game-Semantic Model of Computation

The present paper introduces a novel notion of (effective) computability', called viability, of strategies in game semantics in an intrinsic (i.e., without recourse to the standard Church-Turing computability), non-inductive and non-axiomatic manner, and shows, as a main technical achievement, that viable strategies are Turing complete. Consequently, we have given a mathematical foundation of computation in the same sense as Turing machines but beyond computation on natural numbers, e.g., higher-order computation, in a more abstract fashion. As immediate corollaries, some of the well-known theorems in computability theory such as the smn-theorem and the first recursion theorem are generalized. Notably, our game-semantic framework distinguisheshigh-level' computational processes that operate directly on mathematical objects such as natural numbers (not on their symbolic representations) and their symbolic implementations' that define theircomputability', which sheds new light on the very concept of computation. This work is intended to be a stepping stone towards a new mathematical foundation of computation, intuitionistic logic and constructive mathematics.