approximate but we don't have access to them so let's call that our approximation Q so given B like what what a is most likely well this is the other this should be so basically we were trying to learn two mappings or two conditional distributions and when you specify this kind of conditional distribution distribution Q of a given B you implicitly induce a marginal distribution so when I specify Q of B given a I implicitly specifying a marginal distribution on B and the way that you compute it is if I sample a for