The level of indirection isn’t necessary: the Solomonoff agent’s distribution is a weighted mixture of the outputs of all possible Turing machines, weighted according to the posterior probability of that Turing machine being the one that is generating the observations. Any Turing machine that predicts that the putative halting oracle gets one wrong on a particular trial gets downweighted to zero when that fails to occur.
The level of indirection isn’t necessary: the Solomonoff agent’s distribution is a weighted mixture of the outputs of all possible Turing machines, weighted according to the posterior probability of that Turing machine being the one that is generating the observations. Any Turing machine that predicts that the putative halting oracle gets one wrong on a particular trial gets downweighted to zero when that fails to occur.