All you need to know about Carpenter's Square-2
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Diagram 2.1: White to play

This is what's formally known as Carpenter's Square. 'a' is clearly the key point: black can play there to secure the corner; white normally attacks there. White may also attack from 'b', 'c' or 'd'. Will discuss all possibilities later.


Diagram 2.2: Solution 1

As we will explain later, attaching on the first line is the only tesuji to save this corner. is also a good move (if attaches from one side, should always hane from the other). is also the only move (explained later). The final outcome is a ko fight.

There are two more things to mention here:

1. If black group has one external liberty, the above sequence remains the same, although black has an alternative to (will cover this in Shape 8 later).

2. Because of symmetry, and work exactly the same. However, in real games, the shape is unlikely to be as clean as on a textbook. So how to choose the correct side? Assume that black eventually wins the ko fight, he would have captured and stones, leaving further yose to play on that side. If the surrounding environment is not symmetric, black can in principle choose the side with more valuable yose left (make sense?).

Are there any variations? We will discuss a few:


Diagram 2.3: Black fails

How about ? That would fail miserably. I will leave out a few details for readers to practice. But the key here is always for white to form an eye in the corner (Eye versus No Eye capturing race).


Diagram 2.4: Black fails

in Solution 1 above is the only move. in this diagram is not working - the result is Bulky Five.


Diagram 2.5: White fails

in Solution 1 is also the only move. For example, in this diagram would result in seki.

Solution 1 (Diagram 2.2) is one of the two standard ways to start a ko fight in the Carpenter's Square. In Shape 3 we will discuss the other way.

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