Tit for tat

Tit for tat is an English saying meaning "equivalent retaliation". It developed from "tip for tap", first recorded in 1558.^[1]

It is also a highly effective strategy in game theory. An agent using this strategy will first cooperate, then subsequently replicate an opponent's previous action. If the opponent previously was cooperative, the agent is cooperative. If not, the agent is not. This is similar to reciprocal altruism in biology.

^ Shaun Hargreaves Heap, Yanis Varoufakis (2004). Game theory: a critical text. Routledge. p. 191. ISBN 978-0-415-25094-8.

[1] Shaun Hargreaves Heap, Yanis Varoufakis (2004). Game theory: a critical text. Routledge. p. 191. ISBN 978-0-415-25094-8.

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