Black to live: ko but not ko (Solution Corrected)

In the previous post, I mentioned that this problem is a case of ko with infinite ko threats starting at A.

However, it seems that I was wrong and I missed a very simple variation.

The creator of this problem must have also missed the variation.

The variation is correct up till here.

At this position, I mentioned that white can only throw in at A, allowing black to take back the ko and essentially having infinite ko threats by playing at A1 repeatedly.

However, white playing at A is not the only move here.

Instead, white can throw in here.

Whenever black takes the ko at A, white will find a ko threat and take back, so lets assume white wins the ko.

Black can only take the stone here at 1 locally.

White plays from outside at 2.

Notice that black can’t play at A now because allowing white to take the two stones is not helping black. It will just go back to the same shape and black loses a move.

In this situation, black can continue to fight the ko at B. It’s is a one move approach ko for white, and if white wins one time he can play at C to make it into a direct ko.

In fact, playing at A is not the only move.

White can also play at B or C, and it is still the same result.

Probably in an actual game playing at B will be the best since it’s always better to put your stones outside.

Furthermore, white can even choose to tenuki at this point.

Black cannot live in one move and has to win the ko at C1 and then take the 3 stones.

It’s still a two-move approach ko for white.

Why did we only see this move in this position?

Well, I guess we are too used to the eternal life position shown below, we mistakenly thought that this is the only move now.

However, it’s clear that it’s not the case.

In the case of the above position, then yes A4 is the only move, since playing anywhere else will allow black to live.

In conclusion:

This is a problem that looks like an eternal life but is not.

It looks like a ko problem with infinite local ko threats but it’s not.

In the end it’s just a simple ko problem.

Even though the best solution is nothing special, at least there was an interesting variation inside.

Maybe white can even consider tricking black by playing at A4 first, and when black tries to find ko threat the second time by playing at A1, white can make it into a real ko. 🙂

Real game tsumego: Black to live (from Korean Baduk league)

From a recent Korean Baduk League match.

Kim Jeongheon (B) VS Park Yeonghun

Black’s middle left group is in danger now.

White’s group on the left is also in danger, but white can somehow live using the sente at A9.

It seems that there’s no way for black to live, but the winning rate for black at this point was actually more than 96%.

B played wrongly in the actual game due to time pressure and lost, but there was a way that black could’ve lived by making use of white’s weaknesses.

Can you find it?

Hint:

In the actual game, B played B3, and there was no more chance after white answered at C2.

Full kifu: https://kifudepot.net/kifucontents.php?id=saf%2F1gCCYQbfiet1Tox%2BzA%3D%3D

It’s good to not give up sometimes

I was watching the Female Baduk League on Baduk TV one day and something very interesting happened.

After W made a mistake and got cut by B at the bottom, W was in grave danger as both groups were not alive.

Even though B’s corner is also not alive, B has many liberties and B also has strong influence on both the bottom right and the top right. This makes it a very difficult fight for W. The percentage for B also goes to almost 100%.

W managed to live the bottom group in the end, but the centre is in grave danger now.

Even though it’s W’s turn, B’s strong influence on the top right is waiting for W and there seems to be no way out.

W also doesn’t have enough liberties to go into a capturing race with B on the bottom left.

After struggling for a while, W still could not find a way out.

The cut on top was W’s last struggle.

Game was still good for black.

After W extends the cut stone to aim to capture the centre B group, B attaches the 2 stones.

This looks like a normal move, but from here onwards things suddenly started to go wrong.

It can be seen in the percentage bar as well.

Eventually, B managed to make a ko but W takes the ko first.

W didn’t answer B’s ko threat and took all the centre stones.

B didn’t have any chances after that.

This was the end result.

Who would’ve expected the game to turn out like this?

This was one of the biggest reversals I have ever watched.

Even the commentator also mentioned that he has never seen anything like this before.

A pity for B who had so many chances to win but went down this path eventually.

This shows that sometimes it’s better to keep on playing even when you know that you are losing by a lot.

It also explains why I still like to watch humans play even when AIs can easily beat top pros with handicap nowadays.

For the full video, please refer to below.

The cut starts at 3:01 and the reverse started at 3:19.

19×19 for Go Quest

Previous I talked about Go Quest in the following post:

Go for Go Quest

At that time, only 9×9 and 13×13 options were available. But now they have another option: 19×19!

The timing is still fast game: 5 min per player, with additional 3 seconds per move. This is actually faster than most blitz games, so it’s not really recommended for people who can’t play blitz. Nevertheless, if you want to have a quick game, but doesn’t want to play on a small board, then this is a great option.

The looks of the board and the stone has changed as well. Personally I prefer the previous version, but the stones in this new version looks nicer. 

Not many people play on 19×19 yet, as there were only less than 5 people waiting when I played, compared to more than 10 for 9×9 and 13×13.

It would be better to play on an iPad rather than your phone, especially if your screen is small. However, they have the option for you to double click before playing, so the likelihood of misclick is not that high. 

If you don’t mind the small screen, then having a quick game here is much more convenient then logging to the Go Server and going through the process of finding opponents and agreeing on the time limit. Go Quest does everything for you! You just need to click a button.

You can download Go Quest from the App Store or Google Playstore.