All you need to know about Carpenter's Square - 24
Diagram 24.1: White to play
The extra external liberty makes a lot of difference. What's the best strategy for white?
Diagram 24.2: White fails
We've in fact covered everything we need to know in Shape 23 already. First of all, as shown here, the solution for Shape 23 (Diagram 23.9) no longer works because of the extra liberty.
Diagram 24.3: Seki
Because 
in the previous diagram doesn't work, white has to settle in a seki now, which is a big failure considering ko solutions are available.
Diagram 24.4: Solution 1
By examining the options in Shape 23, it is clear that Diagram 23.4 (repeated here) is the best possible outcome. White can be satisfied that the ko is confined in the corner and 
, a big yose move, is played in sente.
Diagram 24.5: Solution 2
Alternatively, white can choose to form a standard Carpenter's Square, which has been covered in details in Shape 8.
Diagram 24.6: Variation
is also possible. This will be discussed in Shape 28. Just for your information this also results in a ko fight.
Diagram 24.7: Variation
is another possibility. This shape is identical to Diagram 24.4. Only the orders are changed.
Conclusion: with the extra liberty black will not die unconditionally. White can choose from a number of ways to create direct kos.
