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I'm not sure I followed your answer, but in the bottom right box shouldn't it be A -> 70? Not sure if that changes your logic.
Since it seems like few people will be attempting this further, I will give another hint.
Suppose the configuration is (10, 20, 30).
When it gets to Alfred, he knows he's either 10 or 30.
But if he's 10, what would Robin have seen during his first round?
Yes, 70, not 80. Doesn't change my logic though. I'll give it some more thought later using your hint, and see if it agrees or disagrees with my logic.
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