It still seems slightly fuzzy in that other than check/mate situations no moves are fully mandatory and eg recaptures may occasionally turn out to be the wrong move?
Indeed it can be difficult to know when it is actually better not to continue the line vs when it is, but that is precisely what MCTS would help figure out. MCTS would do actual exploration of board states and the budget for which states it explores would be informed by the policy network. It’s usually better to continue a line vs not, so I would expect MCTS to spend most of its budget continuing the line, and the policy would be updated during training with whether or not the recommendation resulted in more wins. Ultimately though, the policy network is probably storing a fuzzy pattern matcher for good board states (perhaps encoding common lines or interpolations of lines encountered by the MCTS) that it can use to more effectively guide the search by giving it an appropriate score.
To be clear, I don’t think a transformer is completely incapable of doing any search, just that it is probably not learning to do it in this case and is probably pretty inefficient at doing it when prompted to.
Indeed it can be difficult to know when it is actually better not to continue the line vs when it is, but that is precisely what MCTS would help figure out. MCTS would do actual exploration of board states and the budget for which states it explores would be informed by the policy network. It’s usually better to continue a line vs not, so I would expect MCTS to spend most of its budget continuing the line, and the policy would be updated during training with whether or not the recommendation resulted in more wins. Ultimately though, the policy network is probably storing a fuzzy pattern matcher for good board states (perhaps encoding common lines or interpolations of lines encountered by the MCTS) that it can use to more effectively guide the search by giving it an appropriate score.
To be clear, I don’t think a transformer is completely incapable of doing any search, just that it is probably not learning to do it in this case and is probably pretty inefficient at doing it when prompted to.