The program begins with tit for tat for the first three moves, except that if it was the only one to cooperate on the first move and the only one to defect on the second move, it defects on the third move. After the third move, its choice is determined from the 3 preceding outcomes in the following manner. Let A be the sum formed by counting the other’s defection as 2 points and one’s own as 1 point, and giving weights of 16, 4. and 1 to the preceding three moves in chronological order. The choice can be described as defecting only when A equals I, 6,7. 17,22,23,26,29,30,31,33,38,39,45,49,54,55.58, or 61. Thus if all three preceding moves are mutual defection, A = 63 and the rule cooperates. This rule was designed for use in laboratory experiments as a stooge which had a memory and appeared to be trustworthy, potentially cooperative, but not gullible.