Hi Mario,

> I am interested in formalizing results about the game of Go as my next
> project. I have have a repository of computer-verified proofs here:
> https://puszcza.gnu.org.ua/projects/hol-proofs/

I am very interested in such a project; please let me know about your
progress! I don't know about your plans, but the foremost thing I want to
do is to determine the theoretical komi for small rectangular boards in a
proof assistant; in particular, to reproduce most and hopefully all results
in the two papers "Solving Go on Small Boards" and "Solving Go for Small
Rectangular Boards". I don't expect tree search to be as efficient in a
proof assistant, but more powerful arguments (or "proof tactics") may
compensate for that. To make things more efficient, it may be desirable to
implement bitboard and hashtable in the proof assistant.

I have been wondering what proof assistant I should use. Coq seems to be a
suitable choice, since people have been using it for retrograde analysis in
chess, and it's also what the machine learning environment GamePad uses. (
https://arxiv.org/abs/1806.00608) But personally I am familiar with neither
Coq nor HOL to judge which will be more efficient for proving facts about
Go.

It's probably hopeless to determine the best play for an arbitrary initial
position, but starting from the empty board, there should be relatively
simple forced lines towards the optimal score under different rulesets: at
least many human individuals have pruned the game tree enough that they are
convinced of the alleged optimal solutions for 6x6 and 7x7, and computers
can be more exhaustive and quicker through automation. That's why I believe
producing formally verified proofs is a feasible task with the advent of
deep learning.

For interested people, this 2015 article is the most comprehensive analysis
of 7x7 Go (by Li Zhe 6p) I've seen:
https://m.newsmth.net/article/Weiqi/615932 "In terms of tsumego difficulty,
6x6 optimal solution is about amateur 6d, and 7x7 is much harder than
Hatsuyōron problems. The most important reason is that a usual tsumego has
only one solution, which is not the case for an empty small board (and we
have no idea how many solutions there are)." Compared to the 7x7 article by
J. Davies, it also explains why some variations do not work.

There has been a debate here 10 years ago about 6x6 komi; now people seem
to have settled that it's 4, but a computer proof is still lacking. If
anyone has trained 6x6 networks with komi's 3.5/4.5 which have nearly
100%/0% initial winrate respectively, that would be very helpful for the
move ordering in the tree search stage (and the winrate would help
determine when to apply other proof tactics), but these are easy to train
nowadays anyway (using Leela Zero or Minigo or whatever).

Best,
Junyan
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