Good question, it's a good ko thread.

I count A19 ko threat as 9 points and the j18 capture as 13 points. White felt that 13 points was less than taking the ko so a 9 point ko threat would not be large enough. Note I am not a very strong player so is just a guess. Edit: looking at again I realize that A19 would have been more than 9 points if white had answered at J18. So maybe it was just that white could see a clear win by ignoring the last ko threat played and felt it was better to just take the win immediately instead of continuing the ko and possibly making a mistake.

I think it was a threat. Maybe Yeonwoo meant that it was clear Ke Jie would get at least those ten points on the top, so no point continuing the ko.

I think it is, I think it's more that Ke Jie's ko threat wasn't bigger than the ko, not that Shin Minjun didn't have any more ko threats.

Unfortunately, baduk population is getting less in Korea but still 9miliion..

Kejie cried when AlphaGo defeated him. Kejie did his best and his pride was hurt.

Net yet

I always forget to adjust 😔 next time i will try!

He was defeated by Ke Jie

Shin Jinseo lost to Ke Jie in the second round, june 2020: you can find the game at go4go.

That was Ke Jie: www.go4go.net/go/games/sgfview/91059

Ke Jie, in the round of 16

Shinjinseo dropped long time ago

Shin Jinseo lost to Ke Jie in the second round, june 2020: you can find the game at go4go.

Yes

I didn't know that lol

@@goproyeonwoo It would be fine if they would put the year first, like in East-Asian countries, but now it is all mixed up.

That's the 'ko' rule. There's a couple slightly different types of ko rules depending on the country/ruleset, but they would both apply the same way here. The important concept is that the board position does not repeat. So one player could not immediately take back the captured stone, because the board would be a repeat of the position from the prior move. Instead, the player can find another part of the board where they can play a move severe enough that it requires a response by the opponent (a ko threat), and that means the board position changes as a result. If the opponent responds to the 'ko threat', now the first player can go back to capture the one stone again, and after that the opponent is the one burdened with finding a 'ko threat'. This bounces back and fourth, and is called a 'ko fight'. It usually ends when one player cannot find a move severe enough that the move forces the opponent to respond, which is what happened to Ke Jie in this game. There are some parts of ko fights that make it harder to judge who is ahead and by how much - the ko threats players come up with can be complicated with their own benefits and losses, and ko threats are rarely urgent moves to begin with so neither player is likely to have spent as much time reading them. So it makes some sense that Ke Jie would try to start one when behind.

After one turn passes you can take back the stone if you like. But than you have to spend another move in order to close it. If it's a key stone, than it would be worth fighting for it. This sequel is called "KO"

It's a ko fight. You can capture back and forth if you make other moves in between each capture. I commented this before but it disappeared. Maybe it was the link, so I'll just advise you to search for ko or ko fight on sensei's library or wherever you like to learn about go.