“…The appealing aspect of integrating features of PAC-learning with Bayesian inference is that PAC-bounds are robust even when the true hypothesis is not included in the hypothesis space. However, known PAC-Bayesian results only imply that probability matching on the posterior is optimal (i.e., provides the tightest PAC-Bayesian bounds) for tasks that already contain in their description some aspect of probability matching, such as estimating a distribution, selecting a hypothesis stochastically, or providing a weighted average (McAllester, 1999(McAllester, , 2003. In fact, for the task of interest to us⎯selecting the true hypothesis⎯PAC-Bayesian considerations imply the same response as rational choice:…”