Yes, yes I was implicitly assuming that the AIXI has already been trained up on the game---the technical argument (which allows for training and explores possibilities like "allow the AIXI to choose the agent machine") is somewhat more nuaunced, and will be explored in depth in an upcoming post. (I was hoping that readers could see the problem from the sketch above, but I suppose if you can't see AIXI's problems from Robby's posts then you'll probably want to wait for the fully explicit argument.)