Each player must play optimally from every information set onward, given prior beliefs and the strategy profile governing future moves

If we assume that players’ beliefs are always consistent with this equality, then we may define a sequential equilibrium. A SE has two parts: (1) a strategy profile § for each player, as before, and (2) a system of beliefs μ for each player. μ assigns to each information set h a probability distribution over the nodes in h, with the interpretation that these are the beliefs of player i(h) about where in his information set he is, given that information set h has been reached. Then a sequential e