Winning Sets of Regular Languages: Descriptional and Computational Complexity

Abstract

We investigate certain word-construction games with variable turn orders. In these games, Alice and Bob take turns on choosing consecutive letters of a word of fixed length, with Alice winning if the result lies in a predetermined target language. The turn orders that result in a win for Alice form a binary language that is regular whenever the target language is, and we prove some upper and lower bounds for its state complexity based on that of the target language. We also consider the computational complexity of membership and intersection problems of winning sets.