Lesson 143: Mastering Carpenters Square (6)
This is another example of a theoretically-made situation. The essential distinction of this shape is the two ¡a-marked black stones on the first line. These two stones make the corner invulnerable to an attempt by the enemy to kill you.
The attacking move of White is already decided, and what matters is Black's answer. Here, Black turns with 1 and the outcome up to Black 5 is a dual-life.
Even though Black attaches at 1, the result is still the same as before, namely a dual-life. Thus, when there are two allied stones on the first line, the corner is safe in the matter of life and death. What you should have in mind is that the Black's position in Diag.1 does not possess any territory as it is. Because White can make a dual-life in sente, Black has to add a move right after it becomes the position in Diag. 1 in order to make the corner territory. However, it is worth only 8 points, so it's not easy to get a chance to play it out.
This situation can happen more often than not because there are many cases where Black bends and connects with 1 and 3. Black's corner looks pretty safe and even big. However, if Black doesn't reinforce the shape, no territory will be left for him.
Of course Black is not killed even though he plays elsewhere. But, as you see, up to 8, Black can live only with a dual-life and even in gote. Therefore, as in the first example, Black has to add a move to the corner if he wants to save the territory.
If White bends at 3 instead of butting with 4, Black should not block at 5 but make an eye with 4. When White connects with 5, Black can make another eye by sacrificing 6 and then descending with 8. If Black plays 5 instead of 4, the corner turns into a ko.
Then, what if there isn't a black stone at x? As you already know, in Carpenter's Square, the x-marked point is one of the vital points.
It is impossible now for Black to make a dual-life by turning with 2 as in Diag.5. After Black 6, White 7 is a good move and the black group is dead.
In this case, Black should turn with 2 and the corner is a ko up to 10, which is the best result for Black. Black also can make a different ko by playing 6 at 7.
The writer is a baduk professor at Myongji University and a professional player of the game.