I played one game on Tygem this morning, which got me promoted to 1d.
Position #34, Black to play in the lower-right quadrant. Several good moves are possible, but I thought I would record a sequence shown by Katago whose idea is not (yet) natural to me.
[go]$$Wc White to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . O . . . . . . . . . X O . . | $$ | . . . O . O O O X X . . . . . X O . . | $$ | . . X O X O X O . . . . . . . . X O . | $$ | . O O O X X X O X X O . . . . . X O . | $$ | . . X X . . . X O O X X . . . . X O . | $$ | . . . . . . . X . O O O X X . . X . . | $$ | . . . . . . . . . . . O O O X . . . . | $$ | . . . , X . . . X X O O X X . X . . . | $$ | . . . . . X . X . O O X X . . . . . . | $$ | . . . O . O O O . O O O X . . . . . . | $$ | . . . . . . . . O X . O X . . . . . . | $$ | . . . . . . . O X . X O X . . . . . . | $$ | . . . . . O . X X . X X . . . X . . . | $$ | . . . O . . . . . O . . . X . , X . . | $$ | . . . . . . . . . . . . O . . O O . . | $$ | . . . . . . . . . . . . . O . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
[go]$$Wc Possible answer $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . O . . . . . . . . . X O . . | $$ | . . . O . O O O X X . . . . . X O . . | $$ | . . X O X O X O . . 3 . . . . . X O . | $$ | . O O O X X X O X X O 2 . . . . X O . | $$ | . . X X . . . X O O X X 1 . . . X O . | $$ | . . . . . . . X . O O O X X . . X . . | $$ | . . . . . . . . . . . O O O X . . . . | $$ | . . . , X . . . X X O O X X . X . . . | $$ | . . . . . X . X . O O X X . . . . . . | $$ | . . . O . O O O . O O O X . . . . . . | $$ | . . . . . . . . O X . O X . . . . . . | $$ | . . . . . . . O X . X O X . . . . . . | $$ | . . . . . O . X X . X X . . . X . . . | $$ | . . . O . . . . . O . . . X . , X . . | $$ | . . . . . . . . . . . . O . . O O . . | $$ | . . . . . . . . . . . . . O . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
The group separates two black groups. White can try to kill one of them. The continuation is not easy to read but anyway White has nothing to lose, since everything happens in Black's area.
Other moves instead of , like L15 or M15, are also possible, with the same idea.
[go]$$Bc Black to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . O . . . . . | $$ | . . . . . . . . . . . . X O . O O . . | $$ | . . X , X . . . . , . X . X . X X . . | $$ | . . . . . . . . . . . . X X . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . O . , . . . . . , . . . . . , X . . | $$ | . X O O . . . . O O O . . . . . . X . | $$ | X . X . O . . . X X O X . . X X X O . | $$ | . X . . . O . . X O X X O . O X O . O | $$ | . . . X . . . O O O . . O . O O . O . | $$ | . . X . . . . . X X X X X X O . O . . | $$ | . . X O . O X . X O O O X . X O O . . | $$ | . O O . . O . X O . . . O . X . . . . | $$ | . . . . . . . X O . O . . . . . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
[go]$$Bc Black to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . O . . . . . | $$ | . . . . . . . . . . . . X O . O O . . | $$ | . . X , X . . . . , . X . X . X X . . | $$ | . . . . . . . . . . . . X X . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . O . , . . . . . , . . . . . , X . . | $$ | . X O O . . . . O O O . . . . . . X . | $$ | X . X . O . . . X X O X . . X X X O . | $$ | . X . . . O . . X O X X O . O X O . O | $$ | . . . X . . . O O O . . O . O O . O . | $$ | . . X . . . . . X X X X X X O . O . . | $$ | . . X O . O X . X O O O X . X O O . . | $$ | . O O . . O . X O . . . O . X . . . . | $$ | . . . . . . . X O . O . . . . . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
[go]$$Bc Black to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . X X X . . . . . . . . . | $$ | . X X X . X X O O X O . . . . . . . . | $$ | . O O O O O O . . O X X . X . X X . . | $$ | . . . . . . . . . O O X . . . . . . . | $$ | . . . . . . . . . O X O O . . . O . . | $$ | . . . . . . . . . . X . . . . . . . . | $$ | . . . O X . . . . . . . . . . . . . . | $$ | . . . O X . . . . . X . O . . O . . . | $$ | . . . O X . X . . , X O . . O O . . . | $$ | . . . . O X . X . . . O X X X X X X . | $$ | . . . O . O X X O X . X O O X X O O . | $$ | . . . . . O O O X X . . . . O . . . . | $$ | . . . . X O O X O . . . . O . O O . . | $$ | . O O O O X X X O . . . . . . O X . . | $$ | . X X O X O . . . , . . . . . , X . . | $$ | . . X X X O . . O . . . . X . X . . . | $$ | . . . . X O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
Answer:
It may be possible to save the marked stones, or at least to use their aji efficiently.
[go]$$Bc Answer $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . X X X . . . . . . . . . | $$ | . X X X . X X O O X O . . . . . . . . | $$ | . O O O O O O . . O X X . X . X X . . | $$ | . . . . . . . . . O O X . . . . . . . | $$ | . . . . . . . . . O X O O . . . O b . | $$ | . . . . . . . . . . X . . . . 4 3 . . | $$ | . . . O X . . . . . . . . . . 2 1 . . | $$ | . . . O X . . . . . X . O . . O . a . | $$ | . . . O X . X . . , X O . . O O . . . | $$ | . . . . O X . X . . . O B B B B B B . | $$ | . . . O . O X X O X . X O O B B O O . | $$ | . . . . . O O O X X . . . . O . . . . | $$ | . . . . X O O X O . . . . O . O O . . | $$ | . O O O O X X X O . . . . . . O X . . | $$ | . X X O X O . . . , . . . . . , X . . | $$ | . . X X X O . . O . . . . X . X . . . | $$ | . . . . X O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
Katago prefers "a", but the subsequent fight is complicated.
[go]$$Bc Followup with a $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . X X X . . . . . . . . . | $$ | . X X X . X X O O X O . . . . . . . . | $$ | . O O O O O O . . O X X . X . X X . . | $$ | . . . . . . . . . O O X . . . 0 . . . | $$ | . . . . . . . . . O X O O . . 9 O 6 . | $$ | . . . . . . . . . . X . . . . 4 3 7 . | $$ | . . . O X . . . . . . . . . . 2 1 . 8 | $$ | . . . O X . . . . . X . O . . O . 5 . | $$ | . . . O X . X . . , X O . . O O . . . | $$ | . . . . O X . X . . . O X X X X X X . | $$ | . . . O . O X X O X . X O O X X O O . | $$ | . . . . . O O O X X . . . . O . . . . | $$ | . . . . X O O X O . . . . O . O O . . | $$ | . O O O O X X X O . . . . . . O X . . | $$ | . X X O X O . . . , . . . . . , X . . | $$ | . . X X X O . . O . . . . X . X . . . | $$ | . . . . X O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
at "b" is inferior but simpler. Black managed to make a big reduction. The stones Q9 are dead but still have aji.
[go]$$Bc Followup with b $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . X X X . . . . . . . . . | $$ | . X X X . X X O O X O . . . . . . . . | $$ | . O O O O O O . . O X X . X . X X . . | $$ | . . . . . . . . . O O X . . . . . . . | $$ | . . . . . . . . . O X O O . . 7 O 5 . | $$ | . . . . . . . . . . X . . . . 4 3 . . | $$ | . . . O X . . . . . . . . . . 2 1 . . | $$ | . . . O X . . . . . X . O . . O . 6 . | $$ | . . . O X . X . . , X O . . O O . . . | $$ | . . . . O X . X . . . O X X X X X X . | $$ | . . . O . O X X O X . X O O X X O O . | $$ | . . . . . O O O X X . . . . O . . . . | $$ | . . . . X O O X O . . . . O . O O . . | $$ | . O O O O X X X O . . . . . . O X . . | $$ | . X X O X O . . . , . . . . . , X . . | $$ | . . X X X O . . O . . . . X . X . . . | $$ | . . . . X O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
Instead of , White may try to kill Black like this:
[go]$$Bc diagonal move $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . X X X . . . . . . . . . | $$ | . X X X . X X O O X O . . . . . . . . | $$ | . O O O O O O . . O X X . X . X X . . | $$ | . . . . . . . . . O O X . . . . . . . | $$ | . . . . . . . . . O X O O . . . O 4 . | $$ | . . . . . . . . . . X . . . . 2 6 3 . | $$ | . . . O X . . . . . . . . 7 . . 1 . a | $$ | . . . O X . . . . . X . O . . O b 5 . | $$ | . . . O X . X . . , X O . . O O . . . | $$ | . . . . O X . X . . . O X X X X X X . | $$ | . . . O . O X X O X . X O O X X O O . | $$ | . . . . . O O O X X . . . . O . . . . | $$ | . . . . X O O X O . . . . O . O O . . | $$ | . O O O O X X X O . . . . . . O X . . | $$ | . X X O X O . . . , . . . . . , X . . | $$ | . . X X X O . . O . . . . X . X . . . | $$ | . . . . X O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
Black is locally dead because "a" and "b" are miai for White, but Black has a tesuji at to kill one of the outside groups and thus live.
Needless to say, I am completely unable to read this in a game, but I thought that is an interesting move and worth remembering. Reading is necessaary to check if the move actually works.
[go]$$Wc White to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X . . . . | $$ | . . . O . . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . O . X . . . | $$ | . . . . . . . . . . . O X O . . . . . | $$ | . . O . O . O X . X X . O X . X . . . | $$ | . O X . . . . O O X O . O X . . . . . | $$ | X O X . X X X X O X O . O X . O . . . | $$ | O X . X O O O O O X O . X O O . O O . | $$ | O . X X . . . . X O X . O X O O X X . | $$ | X X X O O O . X . O X . . X O X . X . | $$ | . O O X . . . . X O X . . X O X X . . | $$ | . . . . . . . . . . . . . . O . . . . | $$ ---------------------------------------[/go]
[go]$$Wc This kills the black group $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X . . . . | $$ | . . . O . . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . O . X . . . | $$ | . 1 . . . . . . . . . O X O . . . . . | $$ | . . O . O . O X . X X . O X . X . . . | $$ | . O X . . . . O O X O . O X . . . . . | $$ | X O X . X X X X O X O . O X . O . . . | $$ | O X . X O O O O O X O . X O O . O O . | $$ | O . X X . . . . X O X . O X O O X X . | $$ | X X X O O O . X . O X . . X O X . X . | $$ | . O O X . . . . X O X . . X O X X . . | $$ | . . . . . . . . . . . . . . O . . . . | $$ ---------------------------------------[/go]
The other natural response, solid connection, doesn't work:
[go]$$Wc Wrong answer $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . X . . . . | $$ | . . . O . . . . . , . . . . . , X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . X . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . , . . . . . , . . . O . X . . . | $$ | . . d c e . . . . . . O X O . . . . . | $$ | . 1 O a O . O X . X X . O X . X . . . | $$ | . O X 2 b . . O O X O . O X . . . . . | $$ | X O X . X X X X O X O . O X . O . . . | $$ | O X . X O O O O O X O . X O O . O O . | $$ | O . X X . . . . X O X . O X O O X X . | $$ | X X X O O O . X . O X . . X O X . X . | $$ | . O O X . . . . X O X . . X O X X . . | $$ | . . . . . . . . . . . . . . O . . . . | $$ ---------------------------------------[/go]
If White a, then Black lives with b. If White b, then Black a, White c and White has two cutting points d and e.
[go]$$Bc answer $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . b O 1 . . O X . . | $$ | . . . X X O . . . O . X 2 O . . X . . | $$ | . . X , O O . . . , . . 3 a . X . . . | $$ | . . . . . . . . . O . X . O . . . . . | $$ | . . X . . . . . . . . . . . . X . . . | $$ | . . . . . . . . . O . X . O . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . X . O . . X . . | $$ | . . . , . . . . . , . . . O . X . . . | $$ | . . . . . . . . . . . X X . O X . . . | $$ | . . . . . . . . . . . . . X X O O . . | $$ | . . . . . . . . . . . . . X O O . . . | $$ | . . X . . . . . . . . . . . X O X . . | $$ | . . . O . . . . . . . . . . . . . . . | $$ | . . X O . . . . . O . . . O . O . . . | $$ | . . X O . X O . . . . . . . . . . . . | $$ | . . X X O O . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
If White block at "a" then Black plays "b" and gets a ponnuki. If White plays elsewhere then Black pushes at "a" and separates White into two groups; one of the groups is almost dead.
The following answer is inferior, I am not sure exactly why:
Position #42. I am Black in this game but this is White to play. Both players missed an important point between moves 56 and 79, until White finally got it.
[go]$$Wc The only move $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . O . O . . . . . . . O . O O O . | $$ | . . O , . . . . . , . . . O X X X O . | $$ | . . X X . . . . . . . . . . . . . X . | $$ | . . . . . . . . . . . . . . . . W X . | $$ | . . . . . . . . . . . . . . . . X . . | $$ | . . . . . . . . . . . . . . . W X a . | $$ | . . . X . . . . . . . . . . X X O 1 . | $$ | . . . , . . . . . , . . . . X O . . . | $$ | . . . . . . . . . . . . . . X O . . . | $$ | . . . X . . . . . . . . . . X . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . O . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . O O . . | $$ | . X O O O . . . . , . . . . X , X . . | $$ | X X X X X O O . . . . . . . . X . . . | $$ | . X O O O X . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
This defensive move is big because it is double-sente, as it awakens the aji of the marked stones and forces Black to defend for instance at "a". Both players thought that the upper side was bigger, but this is not true, Katago doesn't even consider any move there.
Suppose that White plays K16 instead (which White did two moves later in the actual game). First of all, the upper side is still invadable at "c", but Black won't play there immediately. In the game I considered "b" but "a" is better because it is sente, and White shouldn't even connect the stone in atari!
[go]$$Wc Wrong move, continued $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . O . O . . . . . . . O . O O O . | $$ | . . O , . . . . . 1 . . . O X X X O . | $$ | . . X X . . . . . . . . . . . . . X . | $$ | . . . . . . . . . . . . . . . . O X . | $$ | . . . . . . . . . . . . . . . . X . . | $$ | . . . . . . . . . . . . . . . O X . . | $$ | . . . X . . . . . . . . . . X X O 2 . | $$ | . . . , . . . . . , . . . . X O 3 4 . | $$ | . . . . . . . . . . . . . . X O c a . | $$ | . . . X . . . . . . . . . . X b O . . | $$ | . . . . . . . . . . . . . . . . d . . | $$ | . . X . O . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . O O . . | $$ | . X O O O . . . . , . . . . X , X . . | $$ | X X X X X O O . . . . . . . . X . . . | $$ | . X O O O X . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
White can't block at "a", otherwise the sequence b, c, d follows and White becomes a dumpling with no eyeshape. So White must defend at "b", Black continues with "a" and White has no base so must escape to the center.
So since is wrong, White must step back like this:
I was so disappointed after losing the lower left corner and the liberty race at the center that I resigned at this point, however Katago says that the game is still balanced. So what can White to to get back into the game?
[go]$$Wc White to play, do not resign! $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . X . . . | $$ | . . . O O X . . . . . X . X . . O . . | $$ | . . O , X X . . . X . . O X . O . . . | $$ | . . . . . . . . . . . O . X . . . . . | $$ | . . O . . . . O . O . O X . . O . . . | $$ | . . . . . . . . . . . O X O O . . . . | $$ | . . . . . . O O X X X X O X . . . . . | $$ | . . O . . . O X X X . . O X O O . . . | $$ | . . . , . . O X X O O O O O X X O . . | $$ | . . X . . . X O X X O X . X . . O . . | $$ | . . . . . . X O X O X X X . . . . . . | $$ | . . . X X X O O O O O X . . X X O . . | $$ | . . X O X O . . . O X . . . X O O . . | $$ | . . X O O X X X . . X . . . X X O . . | $$ | . . X X O O O X X , . . . . . , O . . | $$ | . O O X O O . O X . . . . . . X X X . | $$ | . . . X O . O O X . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
[go]$$Wc Possible sequence $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . 9 1 . . . X . . . | $$ | . . . O O X . 5 3 7 8 X 2 X . . O . . | $$ | . . O , X X . 6 4 X . . O X . O . . . | $$ | . . . . . . . . . . . O . X . . . . . | $$ | . . O . . . . O . O . O X . . O . . . | $$ | . . . . . . . . . . . O X O O . . . . | $$ | . . . . . . O O X X X X O X . . . . . | $$ | . . O . . . O X X X . . O X O O . . . | $$ | . . . , . . O X X O O O O O X X O . . | $$ | . . X . . . X O X X O X . X . . O . . | $$ | . . . . . . X O X O X X X . . . . . . | $$ | . . . X X X O O O O O X . . X X O . . | $$ | . . X O X O . . . O X . . . X O O . . | $$ | . . X O O X X X . . X . . . X X O . . | $$ | . . X X O O O X X , . . . . . , O . . | $$ | . O O X O O . O X . . . . . . X X X . | $$ | . . . X O . O O X . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
The main point is to use the stone N16 to get a free move at M18, which will make the invasion successful. The invasion is also possible because of the helping stones around H14.
[go]$$Wc White to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . X O . . O O X . | $$ | . O O . O . O O X X . X O O . O X . . | $$ | X O X O . O . . X , X O X . . X X . . | $$ | . X X . . . . X . . O O . . O X . . . | $$ | . . . X . . . X O . . O . . . X . . . | $$ | . . . . . X . . O . . . . . . . . . . | $$ | . . . . . . . . . . . . . O . X . . . | $$ | . . . . X . . . . . . . . . . . . . . | $$ | . . . , . O O O O , X X . X . , X . X | $$ | . . . . X O X X O . O O X . X . X X O | $$ | . . . X . X . . O O . . O . . . . O O | $$ | . . X . . . . X . O . O O . . . X O . | $$ | . . O X . . . . X X O . . . . X X O . | $$ | . . O . . . . . X O . O O O X X O . . | $$ | . . . O . . X . . O . X X . X O O . . | $$ | . . . . . . X O . . . . . . X X O . . | $$ | . . . O . . . O . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
[go]$$Wc Double threat $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . X O . . O O X . | $$ | . O O . O . O O X X . X O O . O X . . | $$ | X O X O . O . . X , X O X . . X X . . | $$ | . X X . . . . X . . O O . . O X . . . | $$ | . . . X . . . X O . . O . . . X . . . | $$ | . . . . . X . . O . . . . . . . . . . | $$ | . . . . . . . . . . . . . O . X . . . | $$ | . . . . X . . . . . . . . . . . . . . | $$ | . . . , b O O O O , X X . X . , X . X | $$ | . . 1 . X O X X O . O O X . X . X X O | $$ | . . . X . X . . O O . . O . . . . O O | $$ | . a X . . . . X . O . O O . . . X O . | $$ | . . O X . . . . X X O . . . . X X O . | $$ | . . O . . . . . X O . O O O X X O . . | $$ | . . . O . . X . . O . X X . X O O . . | $$ | . . . . . . X O . . . . . . X X O . . | $$ | . . . O . . . O . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
[go]$$Wc White to play $$ --------------------------------------- $$ | . X . . . . . . . . . . . . . . . . . | $$ | . O X X . . . . . . . . . . . X O X . | $$ | . O O O X X . O O X X . . . . X O X . | $$ | . . . O . . . . . O . X . . . X O X . | $$ | . . . . . X . . O . . . . . O X X O . | $$ | . . O . . . . . . . . X . . . O O . O | $$ | . . . . . X . X O . O . . . . . . O . | $$ | . . O O O . . . O . O X X . X . . . . | $$ | . . X X O . X X X . O O . . . O X . . | $$ | . . . , . O O O X , . . O . . O . . . | $$ | . . . . X X . O . X . X . . . . O . . | $$ | . . . . O . X O . . . . . . . . . . . | $$ | . . X . X X O X X . . . . . . . . . . | $$ | . . . . . . O . . . . . . . . . X . . | $$ | . . . . . O O O X . . . . . . . . . . | $$ | . . . X X X O X O O O . X . . O X X . | $$ | . . . . X O O X O X . . . O . O O X . | $$ | . . . . . . . X . . . . . . . O X . . | $$ | . . . . . . . . . . . . . . . . . X . | $$ ---------------------------------------[/go]
Answer:
In the game I answered the shoulder hit with "a", but the move I missed was which attacks Black's eyeshape in order to make profit in the center.
[go]$$Wc Answer $$ --------------------------------------- $$ | . X . . . . . . . . . . . . . . . . . | $$ | . O X X . . . . . . . . . . . X O X . | $$ | . O O O X X . O O X X . . . . X O X . | $$ | . . . O . . . . . O . X . . . X O X . | $$ | . . . . . X . . O . . . . . O X X O . | $$ | . . O . . . 1 . . . . X . . . O O . O | $$ | . . . . . X . X O . O . . . . . . O . | $$ | . . O O O . . . O . O X X . X . . . . | $$ | . . X X O . X X X . O O . . . O X . . | $$ | . . . , . O O O X , . . O . . O . . . | $$ | . . . . X X . O . X . X . . . . O . . | $$ | . . . . O . X O . . . . . . . . . . . | $$ | . . X . X X O X X . . . . . . . . . . | $$ | . . . . . . O . . . . . . . . . X . . | $$ | . . . . . O O O X . . . . . . . . . . | $$ | . . . X X X O X O O O . X . . O X X . | $$ | . . . . X O O X O X . . a O . O O X . | $$ | . . . . . . . X . . . . . . . O X . . | $$ | . . . . . . . . . . . . . . . . . X . | $$ ---------------------------------------[/go]
[go]$$Wc Answer $$ --------------------------------------- $$ | . X . . . . . . . . . . . . . . . . . | $$ | . O X X . . . . . . . . . . . X O X . | $$ | . O O O X X . O O X X . . . . X O X . | $$ | . . . O . . . . . O . X . . . X O X . | $$ | . . . . . X . . O . . . . . O X X O . | $$ | . . O . . 2 1 . . . . X . . . O O . O | $$ | . . . . . X 3 X O . O . . . . . . O . | $$ | . . O O O 4 . . O . O X X . X . . . . | $$ | . . X X O . X X X . O O . . . O X . . | $$ | . . . , . O O O X , . . O . . O . . . | $$ | . . . . X X . O . X 6 X . . . . O . . | $$ | . . . e O f X O . 7 5 8 . . . . . . . | $$ | . . X . X X O X X . . . . . . . . . . | $$ | . . . . . . O . . . 9 a b . . . X . . | $$ | . . . . . O O O X . . c . . . . . . . | $$ | . . . X X X O X O O O . B . . O X X . | $$ | . . . . X O O X O X . . d O . O O X . | $$ | . . . . . . . X . . . . . . . O X . . | $$ | . . . . . . . . . . . . . . . . . X . | $$ ---------------------------------------[/go]
Now the marked stone is almost swallowed. Black still needs to defend the central group with a move like a or b. For instance if Black a then White c. If Black b then White d.
Note: several times Katago suggests the exchange White e Black f but I don't understand it.
In the game I captured directly following the proverb to capture the laddered stone at the earliest opporunity, but this is less good than the solution. The move above allows White to play a forcing move
It's clearly better than playing directly. Adding moves and is good for Black, as is almost useless while faces the center and exerts pressure on the white group.
[go]$$Wc White to play $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . O X . O . . . O X X . . X X O O . . | $$ | . O X O . O . . . O . X . O . X O . . | $$ | . O X O . X . . . O . . . X . X O . . | $$ | . X O O X . . . . . . . . . . X X O . | $$ | X . X X O O . . . . . O . O O O O O . | $$ | . X . . X O . . . . . . O X X O X X O | $$ | . . . . X X . . . . . . O . X X X . O | $$ | . . . . . . . . . O . X X X . X X O O | $$ | . . . , . . . . . , O X X O X O X X O | $$ | . . . . . . . . . . . X O O O O X . X | $$ | . . . X . . . . . O . . . . . X O X . | $$ | . . X . O . . . . . . . . . O O O X X | $$ | . X . . . . . . . . . . . . X . . O . | $$ | . . . O . . . . . . X . . . . . O . . | $$ | . . X O . . . O O , . . . . X , . X . | $$ | . . X O . O O X . . X . . . . X . . . | $$ | . . . . . . X . X . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
Black only has one eye but M7 and T6 are miai so Black can connect to a living group. However White has a good endgame move.
[go]$$Wc Answer $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . O X . O . . . O X X . . X X O O . . | $$ | . O X O . O . . . O . X . O . X O . . | $$ | . O X O . X . . . O . . . X . X O . . | $$ | . X O O X . . . . . . . . . . X X O . | $$ | X . X X O O . . . . . O . O O O O O . | $$ | . X . . X O . . . . . . O X X O X X O | $$ | . . . . X X . . . . . . O . X X X . O | $$ | . . . . . . . . . O . X X X . X X O O | $$ | . . . , . . . . . , O X X O X O X X O | $$ | . . . . . . . . . . . X O O O O X . X | $$ | . . . X . . . . . O . . . . . X O X . | $$ | . . X . O . . . . . . . . . O O O X X | $$ | . X . . . . . . . . . . . . X . . O . | $$ | . . . O . . . . . . X . . . . . O . . | $$ | . . X O . . . O O , . . . . X , 1 X . | $$ | . . X O . O O X . . X . . . . X a b . | $$ | . . . . . . X . X . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
[go]$$Wc Blocking at a $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . O X . O . . . O X X . . X X O O . . | $$ | . O X O . O . . . O . X . O . X O . . | $$ | . O X O . X . . . O . . . X . X O . . | $$ | . X O O X . . . . . . . . . . X X O . | $$ | X . X X O O . . . . . O . O O O O O . | $$ | . X . . X O . . . . . . O X X O X X O | $$ | . . . . X X . . . . . . O . X X X . O | $$ | . . . . . . . . . O . X X X . X X O O | $$ | . . . , . . . . . , O X X O X O X X O | $$ | . . . . . . . . . . . X O O O O X . X | $$ | . . . X . . . . . O . 5 . . . X O X . | $$ | . . X . O . . . . . . . . . O O O X X | $$ | . X . . . . . . . . . . . . X . . O c | $$ | . . . O . . . . . . X . . . . . O e d | $$ | . . X O . . . O O , . . . . X , 1 X . | $$ | . . X O . O O X . . X . . . . X 2 3 . | $$ | . . . . . . X . X . . . . . . . . 4 . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
If Black c White d then Black e would be self-atari so Black is dead. Therefore was wrong and should have been at "b". Here is a continuation suggested by Katago:
[go]$$Wc Stepping back at b $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . O X . O . . . O X X . . X X O O . . | $$ | . O X O . O . . . O . X . O . X O . . | $$ | . O X O . X . . . O . . . X . X O . . | $$ | . X O O X . . . . . . . . . . X X O . | $$ | X . X X O O . . . . . O . O O O O O . | $$ | . X . . X O . . . . . . O X X O X X O | $$ | . . . . X X . . . . . . O . X X X . O | $$ | . . . . . . . . . O . X X X . X X O O | $$ | . . . , . . . . . , O X X O X O X X O | $$ | . . . . . . . . . . . X O O O O X . X | $$ | . . . X . . . . . O . . . . . X O X . | $$ | . . X . O . . . . . . . . . O O O X X | $$ | . X . . . . . . . . . . f . X . . O . | $$ | . . . O . . . . . . X . . . 0 . O . . | $$ | . . X O . . . O O , . . . 9 X 8 1 X . | $$ | . . X O . O O X . . X . . . 7 X 3 2 . | $$ | . . . . . . X . X . . . . . . 5 4 6 . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
Next move is at "f". I can't read the fight but the basic idea is that Black is forced to connect in gote at some point, allowing White to save stones around or at least to have a good endgame, using the aji of the stones , and . Anyway these three stones are in Black's area so can be sacrificed without damage if necessary.
Posts: 310 Liked others: 47 Was liked: 249
Rank: UK 2d Dec15
KGS: mathmo 4d
IGS: mathmo 4d
I'm not sure how useful human comments are post AI, but here's a try for coming up with explanations without checking the AI.
48: From what I've seen, just in the upper left, hane connect is particularly popular for AI when white's pincer stone is at D11. Otherwise, I think katago prefers hane connect normally for closer pincers anyway. The key is to threaten either B14 (directly) or prepare with E14, trying to induce white to press at F16. But at F18 has also become played after it was found in alphago teach, released in Dec 2017. It was almost not considered at all (or at least discarded/forgotten) pre alphago. These days it is common enough that I might realise it is better in this position (in a 1hr each game) but still rare.
In your position, hane, connect and jump is still a nice way to get sente locally. However, in this position, there are the weak black stones on the left that can only make a one space jump. This feels like to me the main reason not to make white thicker, especially not C10. Furthermore, the F17 jump can be too close to thickness. That is normally exploited with H17.
Your second KG diagram is interesting. The difference to the first KG diagram seems very subtle. I'm not sure how much difference F17-F18 makes. F17 is further from the C15 cut and not so tight on the E16 liberties, but if W had defended tightly at C13, there wasn't much there anyway. As far as I can tell, the D11 peep is useful aji pretty soon after say E9 and so may be C13 or C15 (if C13 response then A15 endgame + cut + C12 is overconcentrated + some D11 aji remains), though they seem far into the future now.
In the first KG diagram, aji definitely remains, but perhaps it takes a move for B to prepare and threaten it? Whereas in the second diagram as long as black has a move around D11 and E14, the C15 cut becomes a problem that threatens to kill something, especially as white doesn't have the F16 forcing move. In addition white never wants to add another move where white is already low and making one space extensions. Of course, white is thicker here and has the right to fight and not let this happen easily, so it is pretty subtle. I anticipate a sequence like Q6-R17 following, but white attack around C8, D8, E9, F9, G6 remain interesting. Perhaps black can play C9 or D9 to more forcefully exploit the two spaces between C10-C13 though. But for the time being perhaps white is ok. If so, locally I'd like to aim for D11 and D13 by first playing E9. As white is thick, I would be nervous about shape attacks such as D9 from white though or E10-F10-F9-D10-E8-D11 when white has the ladder. I'm not strong enough to know what happens here at a glance.
In your third (hidden) KG diagram, jumping out is certainly something black wants to aim for (or even B14 in extreme scenarios), but it seems early because C10-C12 can get strength by attacking D8 as well as the aji in your fourth diagram. It can feel like you are fighting against nothing and may be chasing E16 into your upper side potential. I don't understand if white can't kill black or it is unnecessary for building territory/saving C12. It is saying I am worried about my weakness at D11, and can still connect underneath later, but I'd be worried if could be played at B17. B17 is a key point for both sides, both big endgame and concerning the connection for both sides. Normally for locally, black delays making the choice between B16 and G17.
47:
oo. Didn't notice that in the ? seconds I spent. Looks very tricky. The M4 peep looks relevant in some variations because if L5 is cut off, so is the escape route for M9, but white also has cutting points. at M8 also wasn't my first instinct, instead at M7, but both have lots of bad aji. I'm imagining M8-L9-K9-L8-L7 or M7-L8-L7-K9-?.
46: hmm, my thought process was
tesuji -> J3 -> yes, seems to work -> no, wait that's too small, why does white care about that? -> black should be attacking not asking for an exchange -> D2 is bad shape -> C3? -> F2 connects C3 but does nothing on other side -> H2 still leaves G5 -> nothing interesting with F8 because G5 is too damaging -> damn, have to connect -> H5 -> but white at J5 is painful -> but oo I still have J3 to annoy white -> ok H5.
I guess the point here is that black has enough liberties with F3 and G6 (though its close) that all that matters is capturing F5. H5 is the most efficient method. If black was low on liberties then G5 is better. If black is low on eyespace then G4 is better.
The reason I would give for a more efficient move to exist locally is that black already has 4 stones trying to capture F5, namely E5, F6, G6 (I would label E6 and F3 as connecting moves, that increase black's liberties instead, and G7 as too far away). Normally 4 stones is enough to capture one stone, so you don't need to add another one at G5. Of course, G6 only blocks F5 escaping in say 60% of local variations and H4 threatens it, but you don't need to play G5 until white threatens to save F5 in those 40% of variations (i.e. when white plays G4). Instead you can block what H4 is threatening. Not sure how easy it is to apply such a principle though.
45: thought process (not so linearly this time):
white G14 doesn't cut -> upper right looks solid though P14 isn't small -> the N10 group isn't 100% but ok especially with G14 aji -> what is happening at D10? -> ooh black J2 looks scary -> what is N3 doing left there! -> defense at N3 still seems risky with shortage of liberties -> is there a G1 tesuji? -> no white wins by one liberty -> read answer
Having read answer, it makes sense, but I think I might well have responded at a too in a game if I didn't have enough time to read that the black group was weak enough. The difference between one eye and two is big. I see that also defends against my worries of J2.
It is very cute that as white has J9 in sente, black E10 is no longer sente, making white D9 a threat in combination with the B11 hane. Exact move order I don't know but imagine after e-f exchange, D9-D10-B11-B10(?)-E10-C10-B9-A10-C9. White wins by one liberty. Another aji to read is D9-B10-E10-D7-B9-B8-D10-A9-B11 but as E10 is still valuable, I think D9-E10 is fairly likely.
Perhaps you prioritised safety for white's groups too much, but I think it is fairly normal in this situation.
44: Thought process:
G8 interesting -> probably captured -> hmm no H7 is short on libs -> but still captured -> everything else seems connected and alive -> G5? -> still no -> F14 -> G13 is a cut -> E14 needed first -> is E12 a tesuji? -> needs reading -> R2 annoying ko -> O15 annoying but might not work given O12 -> oh wait is it just C9 -> how did I miss that? -> is black even not alive at top? -> hmm, I think black is only ko for life -> not sure then.
43:
lots of reading at F8 -> looks close to creating something but can't capture anything and G10 doomed -> ?? -> read answer ah, it is easy to forget that N12 is alive. Still it's difficult to find the right sequence even when you know you have to attack that black group. In the final position white's group seems pretty vulnerable, but I couldn't see a way to attack severely. J19 is the standard tesuji; if B starts at G18, I think white can even block at H18 and be alive, but K19 may well still be better; if B starts at K19, white has enough liberties to even consider G17. Note that white always threatens to cut at L16 as white hasn't played N15 to short their own liberties. Black doesn't even seem to have any eyes yet, so needs to attack the group at the top accurately. That's pretty complicated.
42:
Once I see white's threat I see. Misread explanation of third diagram as "White should even connect the stone in atari" -> what?? white is on the verge of death -> oh I misread.
37:
I think can consider playing at K3 to avoid the white's O2 life making tesuji. My ideal sequence is
[go]$$Bc answer $$ --------------------------------------- $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . O . . . . . | $$ | . . . . . . . . . . . . X O . O O . . | $$ | . . X , X . . . . , . X . X . X X . . | $$ | . . . . . . . . . . . . X X . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . O . , . . . . . , . . . . . , X . . | $$ | . X O O . . . . O O O . . . . . . X . | $$ | X . X . O . . . X X O X . . X X X O . | $$ | . X . . . O . . X O X X O . O X O . O | $$ | . . . X . . . O O O . . O . O O . O . | $$ | . . X . . . . . X X X X X X O . O . . | $$ | . . X O . O X . X O O O X . X O O . . | $$ | . O O . . O . X O 1 8 7 O 5 X . . . . | $$ | . . . . . . 6 X O 2 O 4 3 . . . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]
at L3 is ko for life. But it isn't trivial for black to fight either as white is so thick. However, looking at this diagram compared to KG's variation, KG's variation seems better both for endgame and life as P2 is a valuable move to prevent S2. The only thing my diagram gains is to reduce white by around 2 points. Furthermore, is probably better at J1. Although is a tesuji, black is happy to force white into it because black gains by answer everything. I was too aggressive in my variation.
Thank you for your comments, I will read them in more detail tonight (no time right now), but to answer to
Quote:
I'm not sure how useful human comments are post AI
Yes, I am very interested in human comments, whether coming from stronger players like you or from weaker players who have been silent so far. An AI can only show the main lines and answer my questions, but cannot think about all the variations that might be played in a game between humans.
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jlt
gennan
directly.
forces 
because it threatens "a".
separates two black groups. White can try to kill one of them. The continuation is not easy to read but anyway White has nothing to lose, since everything happens in Black's area.
, like L15 or M15, are also possible, with the same idea.
should be played later in the game, the local sequence can stop at 
.
at "b" is inferior but simpler. Black managed to make a big reduction. The stones Q9 are dead but still have aji.
to kill one of the outside groups and thus live.
was wrong and should have been at "b". Here is a continuation suggested by Katago:
is at "f". I can't read the fight but the basic idea is that Black is forced to connect in gote at some point, allowing White to save stones around 
or at least to have a good endgame, using the aji of the stones 
, 
and 
at 
because of the threat at "a".
if white can't kill black or it is unnecessary for building territory/saving C12. It is saying I am worried about my weakness at D11, and can still connect underneath later, but I'd be worried if