Figure 1. Deterministic strategies in the Prisoner's Dilemma.

Each automaton defines a different strategy for how a player behaves during the game. If a player is in state , she will cooperate in the next move; if she is in state , then she will defect. The outgoing transitions of a state define how the state of an automaton will change in response to cooperating (label c) or defecting (label d) of the opponent. The left state with the small incoming arrow corresponds to the initial state of a strategy. The 26 distinct strategies (automata) are classified into four categories: (i) sink-state C strategies, (ii) sink-state D strategies, (iii) suspicious dynamic strategies, and (iv) hopeful dynamic strategies. The automata with the blue background shading contain a conditional cooperation element (Fig. S1 in File S1) which ensures the benefit of mutual cooperation but also avoids being exploited by defection-heavy strategies.