There is one more lesson that I have learned: the strategies which I considered most beautiful (U and C1) played poorly and were the first to be eliminated from the pool. Both U and C1 tried to experiment with the opponent's behaviour and use the results to construct a working model thereof. But that didn't work in this setting: while those strategies were losing points experimenting, dumb mechanical tit-for-tats were maximising their gain. There are situations when the cost of obtaining knowledge is higher than the knowledge is worth, and this was one of such situations.

I think the problem with U was that in practice it quickly wound up playing all defect against tit-for-tat style strategies.