Neat problems from real games

[uzaya]

Attempt

C3- E4 B3- D5 A4 takes the corner? And I guess C3- B3 E3- D2 E4- E2 F3- G4 F2- gains lots of poins in sente (and I assume black playing F8 at any point can be replied with E8.)

[antonTobi]

Black to play:

[jlt]

My answer: A5 A7 D4 A3 B1

[antonTobi]

Correct! In the game my opponent played D4, I quickly responded at A7 and then immediately facepalmed as I realized the missed opportunity

AI Sensei | antonTobi (2123) vs hara1010 (2223)

[jlt]

Not very hard, but easy to miss. White to play.

[shinuito]

Locally or are we looking at a move like r12 or?

Or are we looking at like a G6 wedge?

[uzaya]

Attempt

R12? black cannot defend with Q12 since R12 Q12 Q13 R13 R10 captures the three stones, but I cannot really tell whether black can live there. Still getting some territory with sente should be good I believe.

[martin3141]

Solution

G6 kills

[jlt]

Yes, Martin is correct. R12 is a big endgame move, but is much smaller.

[jlt]

Black to play.

[shinuito]

Oh

I wonder is it something like

B D6, and then if white takes the eye on the left with A9 or A8 or something, then there’s

B F6, E5, D4

And with either W E3 or D5, the idea might be to get an Atari at b4 and capture at least the two white stones at b5, b6?

But probably lots of options for white to back out and give up different stones, or just let black live.

[jlt]

Correct! After Black B4, White could get a ko with B3 but White doesn’t have enough ko threats.

[shinuito]

Ah that’s neat also. Something to watch out for, I was finding that a bit hard to visualise. I’ll have to practice that and other ko like shapes and see if it gets easier to spot from a few moves away

[Jon_Ko]

Huh, I would have followed up D6 with E3 directly, missed the B4 atari.

…okay, clearer now

[antonTobi]

Black to play:

[antonTobi]

Solution

In the game black captured the ko at J1, which is natural, but a huge blunder because white has the ko threat at A7:

(after black responds white captures back at H1 and black will die)

The only winning move for black is to pre-emptively connect at 1, to remove the threat:

[jlt]

Can White do something in the corner?

[antonTobi]

Attempt

T18 S17 Q18 R18 R19 (seki)

T18 S18 S17 (black can fight ko or live with R18)

My first instinct was to start at white R18 which looks fancy, but unfortunately doesn’t go anywhere after black Q18.

[jlt]

White to live.

[antonTobi]

Lovely problem! Never saw this kind of technique in the corner before.