Variations about this second-line cut in the corner. Including a very hidden move that blew my mind when I saw it. Seriously, click this if you didn’t see the variation on WeiqiTV.
The shape in question can happen in various ways. E.g. White could resist to Black’s peep. Then Black can push-cut at c5.
Or White played the keima earlier at d6. To Black’s tsuke-koshi, White cannot block at d5 for whatever reason, but clamps at 2.
So when Black cuts inside, White decides to connect at 4 instead of capturing at 5, either because Black cuts b6 and pulls out b7, or because White cannot resist to Black’s hane e6, making the initial resistence meaningless.
White can try a semeai in the corner. Note that Black’s exchange of c3+d2 for White’s d4+e5 turtle is mostly not profitable.
Who wins the semeai?
When Black starts taking liberties, White can win by 1 liberty thanks to the cut at 12. Even so, we rarely see White resisting the initial peep like this:
After capturing 3 stones, White’s corner actually became smaller than before (shrunk from 15 to 8 points) and Black fortifies his position in sente. The stone at d6 must be really important in order to outweigh these losses.
Now, this is nothing new for dan players. This was also shown in a game review in a WeiqiTV video. Meng Tailing 6p mentioned these variations in his commentary of the game against Gu Li 9p. Below you can see the whole board. The cut was not played in the game, but he did put detailed variations. Brace yourself for what comes next.
Black can start taking a different liberty. When White cuts, Black can kosumi once and make a tetris.
Of course, it is assumed that Black has 1 (one) mega-kothreat somewhere on the board in order to initiate this. That means, when White extends at 22, Black is able to win the ko in the corner.
Actually White can capture Black’s tetris unconditionally. But later on, White is locally dead.
Isn’t this amazing?!
It seems that the reason why Black did not play this sequence is White’s resistance hanetsugi 8 and 10, in the screenshot below. And then the sequence somehow works for White.