all tractable in this case we only really need to make one conditional distribution tractable there are a few properties that we'd like to be able to guarantee that impose a few extra requirements on G in particular if we want to be sure that we're able to recover the training distribution we need to make sure that X has a higher dimension than Z or at least an equal dimension this is just to make sure that we aren't forced to represent only a low dimensional manifold with an X space an interesting thing is that it's actually