A strategy for the iterated prisoner's dilemma in which a prisoner cooperates on the first move, and thereafter copies the previous move of the other prisoner. Any better strategy has more complicated rules.
Tit-for-Tat
See also
Prisoner's DilemmaExplore with Wolfram|Alpha
References
Goetz,
P. "Phil Goetz's Complexity Dictionary." http://www.cs.buffalo.edu/~goetz/dict.htmlReferenced on Wolfram|Alpha
Tit-for-TatCite this as:
Weisstein, Eric W. "Tit-for-Tat." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Tit-for-Tat.html