I don't think saturn's method works, unfortunately, because I can't tell why Jeffreyssai has played C in the past. It could be because he actually uses a decision theory that plays C in one-shot PD if Player1.C <=> Player2.C, or because he just wants others to think that he uses such a decision theory. The difference would become apparent if the outcome of the particular one-shot PD I'm going to play with Jeffreyssai won't be made public.