[FRIAM] Adversarial Go trick defeats KataGo

[Alexander Rasmus]

Jon will probably chime in with his annoyance as well, but the headline
here is fake. In particular, they have bungled the implementation of how a
game of Go is scored severely to get the paper result. The key
"technicality" of the paper, quoting from the article, is:
"As a result of its [KataGo's] overconfidence in a win—assuming it will win
if the game ends and the points are tallied—KataGo plays a pass move,
allowing the adversary to intentionally pass as well, ending the game. (Two
consecutive passes end the game in Go.) After that, a point tally begins.
As the paper explains, "The adversary gets points for its corner territory
(devoid of victim stones) whereas the victim [KataGo] does not receive
points for its unsecured territory because of the presence of the
adversary's stones.""

Summarizing: KataGo gets so far ahead that it passes, the adversarial ai
also passes, and they then hand the game to an incorrect scoring mechanism.
KataGo maintains a score estimate of the game on its own in addition. To
neatly transpose this to the situation of two human players, we will treat
the incorrect scoring mechanism as if it is the adversarial nets estimate
of the score.

So, we have a good player vs a bad player, they both pass (tentatively
ending the game), and they disagree on the score of the game. How this
resolves depends on ruleset (though if you're playing casually the solution
is almost always to resume play). Quoting from Wikipedia, which seems to do
an okay job on this:
---quote---
"Counting phase:
Customarily, when players agree that there are no useful moves left (most
often by passing in succession), they attempt to agree which groups are
alive and which are dead. If disagreement arises, then under Chinese rules
the players simply play on.

However, under Japanese rules, the game is already considered to have
ended. The players attempt to ascertain which groups of stones would remain
if both players played perfectly from that point on. (These groups are said
to be alive.) In addition, this play is done under rules in which kos are
treated differently from ordinary play. If the players reach an incorrect
conclusion, then they both lose.

Unlike most other rulesets, the Japanese rules contain lengthy definitions
of when groups are considered alive and when they are dead. In fact, these
definitions do not cover every situation that may arise. Some difficult
cases not entirely determined by the rules and existing precedent must be
adjudicated by a go tribunal.

The need for the Japanese rules to address the definition of life and death
follows from the fact that in the Japanese rules, scores are calculated by
territory rather than by area. The rules cannot simply require a player to
play on in order to prove that an opponent's group is dead, since playing
in their own territory to do this would reduce their score. Therefore, the
game is divided into a phase of ordinary play, and a phase of determination
of life and death (which according to the Japanese rules is not technically
part of the game)."
---endquote---

So, for Chinese rules, they play on and KataGo will almost certainly 'win'
in a final sense, though if we assume both bots continue on with the same
strategy, the rest of the game will consist of a countable number of passes
and no other moves. For Japanese rules, we are probably best off just
taking the guidance to assume 'perfect play' from both players to mean that
we have either AlphaGo Zero or KataGo take over both positions and carry
on--almost certainly leading to a victory by KataGo.

If you encountered this in person, it would basically consist of a bad
player playing terribly, insisting that they're ahead when they're not, and
then continuing to argue the point indefinitely instead of playing the
game. I don't think there's a neat transposition to chess due to the
difference in how the games end, but the idea is probably something like
someone playing the offensive portion of a fool's mate and then insisting
they won even though it was successfully defended against. I can 100% make
a bad scoring algorithm for chess which declares this a winning strategy,
but that doesn't mean anyone should care...

Assuming that the scoring mechanism in the paper is the same one used when
scoring, e.g., AlphaGo Zero or KataGo self-matches (I do not know whether
this is true), the correct headline would be something like "Adversarial
net identifies inaccuracy in Go scoring algorithms used to train AIs." This
would still be an interesting result, as you're demonstrating that KataGo
can be tricked into "losing" when using the determiner of victor it was
trained with. However, what they've identified is a region of play where
the scoring mechanism is diverging from the game of Go, rather than a
region of play where KataGo is bad at Go itself. Perversely, this would
indicate that KataGo is MORE robust at the game of Go than the scoring
mechanism it was trained against, which is the opposite of what the paper
is saying directionally.

Best,
Alex



On Thu, Nov 10, 2022 at 11:24 AM Roger Frye <frye.roger at gmail.com> wrote:

>
> https://arstechnica.com/information-technology/2022/11/new-go-playing-trick-defeats-world-class-go-ai-but-loses-to-human-amateurs/
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