All you need to know about Carpenter's Square - 15

Diagram 15.1: White to play

Black's condition appears to be slightly better than in Shape 14 because of the extra Black square bend. What can white do now?

Diagram 15.2: White fails

While White 3 works well in Diagram 14.4, it doesn't work here. The extra bend Black square is perfect now to enlarge the eyespace. After *b10*, note that white can only form a seki by playing 'a' (this is not Bulky Five).

Diagram 15.3: Solution 1

White 3 works well in Diagram 14.3 and it continues to work here. Both White 3 and White 5 are forcing moves. White can form an eye in the corner to win the capturing race by one liberty. Black 'a' instead of Black 4 doesn't help either as the common liberty belong to the side with an eye. So black corner is killed.

Diagram 15.4: white is tricked

Black 2 doesn't feel like a good move but white needs to be careful. White 3 is tricked. After *b6*, although black's shape is very ugly, white cannot kill it. Black 8 is a famous tesuji to create a ko fight.

Diagram 15.5: Variation

White 9 doesn't work either but black need to know to play Black 10 instead of 'a'.

Diagram 15.6: Solution 2

Luckily for white, the right solution is still at White 3 - easy to remember. White 7 is the best move, leaving 'a' and 'b' as miai points, resulting in Eye versus No Eye capturing race.

To summarise: surprisingly the extra bend doesn't help black. White can following either Diagram 15.3 or Diagram 15.6 to kill the corner. Just remember that 1-2 is the key point.