> That's why you can solve a single subgame in Two Envelopes game independently of other subgames, even though it's an imperfect-information game. Obviously th

> That's why you can solve a single subgame in Two Envelopes game independently of other subgames, even though it's an imperfect-information game. Obviously the EV of envelope 1 is the contents of envelope 1. If you know the probability of reaching it you can calculate the expected value of that envelope by multiplying by the probability of reaching it. But why are you multiplying by 1/2? Probability is defined in terms of sets. What are the set that makes it 1/2? Does that set contain only the subgames that are part of the subgame you are in?