A Nakade Question

I have a question about an apparent nakade that has two possible continuations if it were played out, one that kills and another that doesn’t. In such a situation (under Japanese rules), is the player required to demonstrate that he knows the proper continuation by playing it out, or is the opponent’s group considered already dead without playing it out, as in a normal nakade?

Specifically, I saw the following position while watching games (sorry, I don’t know how to create and import a board position): Black stones on A1, B1, C1; White stones on A3, B3, B2, C3, D3, D2, D1, surrounded completely on the outside by Black. If this were not in a corner, with the three Black stones surrounded and White surrounded, it would be seki. However, in the corner, Black can kill with A2 making bent four in the corner. But if Black is a beginner and plays C2, then White can live. So, is this still considered a nakade that doesn’t need to be played out, or must Black demonstrate his knowledge? The autoscore scored White as dead with no playout. I’m inclined to think the playout should be required, but I don’t know if it is, and I don’t see an explicit answer in SL.

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What @Conrad_Melville is talking about.

This shape is called bent 4. Under Japanese rules, it is unconditionally dead, black doesn’t need to play it and defend their ko threats.

With unremovable ko threats (like a double ko seki) if none of the players can give up the corner or the seki, it is jigo.


I know about bent four in the corner. That is the variation that kills if it is played by Black. But I don’t see it as bent four in the corner. It seems to be a 3-stone nakade that could continue in two different ways. And if Black is a beginner and plays C2, the result is a live four when White captures.

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If black doesn’t play C2 the corner is dead. Not knowing it’s not a seki doesn’t make it a seki.

If we were talking about this corner, I think you wouldn’t ask “should we consider it killable because a beginner can play d1?”

Edit: of course, if both players agree that it’s seki, it’s counted as a seki.

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Sorry, I don’t think that is exactly comparable. In your example, the mistake would occur in response to White playing inside. Such a mistake is far less likely, though I have seen it happen. In contrast the other situation would seem to require Black to make a choice first, not as a response. It seems very weird that three stones, not four, are considered Bent Four in the Corner. It seems to me that there is no Bent Four in the Corner until Black actually creates it. When people (and SL) speak of “not playing it out,” it has always referred to not playing out the ko, which I understand. It’s very unfortunate that SL doesn’t more explicitly cover my question. I guess I need to do the legwork of checking the Japanese rules.

Thanks for responding, and thanks for the diagrams.


I guess it depends on the context as well.

I think if two players agree to score a game a certain way, except under special circumstances then that’s the way the game is scored. So if both players agree I don’t think one has to demonstrate anything.

While one could appeal to a superhuman bot to objectively determine statuses and scores we have seen some problems with that in other threads. So I guess one has to accept in some case that the way some games are scored are adapted to our level and knowledge. Playing the same game again after significant improvement might result in a different outcome.

That’s the kind of agreement phase I guess that’s necessary in territory rules like Japanese rules where to actually capture things loses points. In area scoring rules, one at the end could capture anything that’s disputed without being penalised and the bent 4 status in area scoring rules can kind of the depend on the whole board, as one might need to decide between fighting the ko and accepting a seki.

Now back to the context again, I guess it depends on whether one thinks of in person games and online.

It’s probably quite an extra bit of hassle to demand an opponent to explain why every group on the board is dead, in the cases where there might be some room for mistake. Similarly we don’t really have a special life and death confirmation phase on OGS that one would probably need to settle status disputes fairly. I guess sharing a variation in some situations could work but it’s not really perfect.

I guess in irl tournaments it probably is the case that if questioned one should be able to demonstrate why a group should be marked dead, and then the board returned to its initial state. Or possibly one might need to demonstrate it on another board, if not using some trick with single convex stones etc.


To respond to what I believe was the core of the initial question, in this position:

If black (at the end of the game) claims that the white group is dead, white may ask black to show how it is dead. The details of how this works depend on the ruleset and the practicalities of the situation. But in all cases, if white for instance believes that black may play C2 instead of A2 when trying to kill, white is fully within their rights to ask black to demonstrate the kill. This is true for all dead groups, there is nothing special about this shape.

It is completely up to white whether to demand this demonstration or not. It would of course be a waste of time to do it in every game with every dead group.

The above is about how the rules “should” work in the abstract. There are some limiting details about what is practical to do on OGS, especially under Japanese rules. Since there is no easy way to do a hypothetical playout, one could try to reach a conclusion by discussing in chat and posting variations.

Edit: To further expand on the differences between the main rulesets, in Chinese rules you would simply continue the game and the new position you reach will be the one you score. Thus if the black player makes the mistake of playing C2 the group will live and that will be that. However, in Japanese rules the playout is only hypothetical. I’m not sure about the details of whether black may make a wrong move, then just ask to try again from the beginning. I’ll let someone more read up on the Japanese rules comment on what would happen in the case where black doesn’t know how to kill, but the white player (and let’s say also a referee watching the game) do know how to kill the white group.

The main thing I wanted to clarify is that there are no groups that are dead “just because they’re dead”. In all modern rulesets, including Japanese rules, dispute is settled through playout. It is only the details of that playout that differ between different rulesets.

(at least this is my understanding, I’m sure someone will correct me quickly if I’m wrong! :slightly_smiling_face:)


This pattern is actually widely known as “bent four in the corner”. Even though the pattern does not immediately look like that, it can be reduced to such through optimal hypothetical play. It is a prototypical example cited in the Sensei’s Library page linked by @_Sofiam above.

It would be a mistake for either player to play another move in that corner. It is kind of like a seki (but not actually a seki, since White is simply dead) before the game ends. Clearly, any additional move by White is self-atari that just loses all of the stones anyways. Another move by Black at A2 would turn the status of the corner into a ko fight, since it would be followed by White at C2, then Black at B1, and White at A1, starting a ko fight to settle the status.

However, it is a mistake to actually play this out in the game (since Black would need to be able to win the ko fight and waste an additional moving filling in one point of eventual territory to finally settle the ko fight), and Black is not required to actually play this out during the game to assert that it is dead. Instead, life and death status is settled by analysis of purely hypothetical playout that applies different ko rules. If the players simply resumed the game, it might not be possible for Black to actually win the ko fight, if White has large unremovable ko threats. However, the curious thing about Japanese rules is that White is still dead in this corner, and Black does not have to prove anything by actually continuing the game, even if there are large unremovable ko threats, since the ko rules are actually different when resolving life and death after the players have passed.

I’ve written about this pattern extensively in other forums posts.

Under Chinese rules, the status of this type of shape can be very different, given the global ko threat situation:


However, it seems that maybe the essence of the original question was not just about the proper status of the position (of course, between two intermediate players that understand the Japanese rules, they would simply accept the position as dead for White without any further play), but rather how to handle the potential practical issues of handling a disagreement that might arise in practice between two beginners??

That is, what should an arbiter do when called over to judge a game with such a disagreement? Should Black be required to state the correct hypothetical line of play (i.e., filling A2 instead of C2 next)? In practice, if I were called to judge such a game, paused during the scoring phase with this dispute unsettled, and if White was trying to argue that it was a seki (and maybe saying something about having ko threats), and if Black simply said something like “no it’s dead as a bent-four and I don’t have to actually play it out because we’re using Japanese rules”, then I probably would feel that Black understands how to hypothetically kill without needing to ask them about any further specifics.

But, what if Black simply said something like, “White is dead here”, and White said “No, it’s seki”? Should the arbiter ask a follow-up question to Black, something like “please provide the hypothetical line that kills White”? If Black responds correctly, then it’s just like above, but what if Black gives the wrong explanation and says, “well, under hypothetical play, Black would continue at C2…” and then White follows up by pointing out that it becomes a living bent-four (not in the corner) in that case? Both players have misunderstood how to correctly determine the life and death status. So, should the arbiter rule it as a seki? Or as White lives? Or should the arbiter correct the misunderstanding of the players and explain how White is dead under the optimal hypothetical play? I actually tend to lean toward the latter possibility, since I think that when the arbiter is called in, it’s their job to help determine the correct status, regardless of some potential misunderstanding by the players, and this is such an elementary position that many should be familiar with. It just seems to be a bit awkward for the arbiter to allow the players make the incorrect determination of life and death, when called in to settle a dispute. Regardless of any potential ways to judge the final position, I think that it would definitely be inappropriate to suggest that the players instead resume the game, and settle things by actually playing things out (since that applies the normal ko rules, rather than the special ko rules used during the life and death determination phase).

It’s also quite messy when two beginners have to figure out how to properly score this situation without any help from an arbiter. They might just both simply misunderstand how to properly apply the Japanese rules. Or, perhaps, it could frustratingly be the case that one of the players is aware of the correct status and the other might not accept the explanation of how to properly apply the Japanese rules. Unfortunately, since the Japanese rules are very complex, and quite unfriendly for fully teaching to beginners, virtually all beginners are just taught an incomplete, oversimplified, and often inaccurate explanation of how to properly determine life and death under the Japanese rules. I think the bent four in the corner is a probably one of the most likely cases where such gaps in understanding are finally brought to light.


Thanks, all. I accept the explanations, although it still seems to me that the position should require one more move. I never imagined playing it out fully, because I have long known that Bent Four in the Corner is dead under Japanese moves. I handled several Bent 4 disputes when moderating, but they were all the simple, four-open-points variety, not with stones in a nakade or with an extra point that could be played to create a live 4.

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There are still some subtleties that I think need to be clarified:

If Black continues play with another move at A2, then it turns into an active ko fight, where Black must both win the ko fight (which won’t work out if White has big enough ko threats) and play another stone to finish the ko (costing a point of territory). Hence, playing another move, at best, costs Black to lose one point, or at worst, loses more by losing the ko fight.

The whole point is that the position does not require one more move, i.e., White is still dead even if they have huge, unremovable ko threats, and Black does not have to waste another point by resolving a ko fight. Black can completely avoid fighting a ko that they cannot win, and still get the benefit of calling that White group dead.

Note that the current 1989 Japanese do not simply just say “bent four is dead”, but rather it is a logical consequence of a convoluted life and death determination procedure.

It is actually possible to have a position with two adjacent copies of this shape, where they are both alive in seki: (see The undead bent fours in the corner)

Are you referring to this shape?


This is quite literally a bent-four in the corner and it is actually unsettled. This one does require another move, since another move by Black would live outright, and another move by White could start a ko fight to possibly kill. Technically, if both players pass with this position unresolved, and the rest of the board was close enough that it mattered, then the game could actually end with both players lose (if Black does not have enough threats to win ko fight). Even if Black has enough ko threats to win the ko fight, they still need to play another move before passing to make the group alive, since the peculiar life and death determination procedure of the Japanese rules would otherwise imply that the position is dead.

I go over all of these points in detail in the posts that I linked above in A Nakade Question - #8 by yebellz


I think the crux of Conrad’s question is:

  1. To apply Japanese rules to resolve status questions, one needs to consider optimal hypothetical play
  2. Is it the sole responsibility of the players to work this out, or can the referee/moderator help them?
  3. In the case that neither the players nor moderator are skilled enough to provide the optimal hypothetical play, what happens?

To which the answers are:
2. Referee can help.
3. The rules cannot be applied correctly.

Point 3 was one of the chief reasons the BGA decided to adopt AGA style rules, in which it is left to the players’ skill (or lack thereof) to play out and resolve disputes (so the fact our main referees are 3k and 1k doesn’t matter).


Do you though? I feel like that’s if you want to score the game ‘correctly’ in the sense of this is how pros or katago would score the game. But human knowledge at all levels is incomplete, although past a certain point at least a decent number of games can probably be scored ‘correctly’ without a rules dispute. I won’t completely rule out some unlikely cases that the Japanese rules doesn’t fully exposit or at least the versions we have access to don’t seem to cover.

But yes I think this is also fine and probably a reasonably good decision and basis for a decision. I think if one just did a hypothetical play phase and then returned to the finished board, accepting the status of groups from hypothetical play, then one could also

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