On the Existence of Reactive Strategies Resilient to Delay

TL;DR

This paper compares two types of infinite games modeling asynchronicity in reactive synthesis, establishing reductions, analyzing randomized strategies, and exploring probabilistic winning thresholds to deepen understanding of game determinacy.

Contribution

It introduces a reduction between games under delayed control and delay games, analyzes randomized strategies, and investigates probabilistic winning thresholds, revealing differences in game determinacy.

Findings

Existence of sure winning strategies can be transferred between game types.

Randomized strategies can favor the protagonist or alter game outcomes.

Winning probabilities can be precisely tuned, showing non-determinacy in certain game settings.

Abstract

We compare games under delayed control and delay games, two types of infinite games modelling asynchronicity in reactive synthesis. In games under delayed control both players suffer from partial informedness due to symmetrically delayed communication, while in delay games, the protagonist has to grant lookahead to the alter player. Our first main result, the interreducibility of the existence of sure winning strategies for the protagonist, allows to transfer known complexity results and bounds on the delay from delay games to games under delayed control, for which no such results had been known. We furthermore analyse existence of randomized strategies that win almost surely, where this correspondence between the two types of games breaks down. In this setting, some games surely won by the alter player in delay games can now be won almost surely by the protagonist in the corresponding game under delayed control, showing that it indeed makes a difference whether the protagonist has to grant lookahead or both players suffer from partial informedness. These results get even more pronounced when we finally address the quantitative goal of winning with a probability in $[0,1]$. We show that for any rational threshold $\theta \in [0,1]$ there is a game that can be won by the protagonist with exactly probability $\theta$ under delayed control, while being surely won by alter in the delay game setting. All these findings refine our original result that games under delayed control are not determined.