Lesson 2 - The Crane's Nest Tesuji
A tesuji is the best move in a tactical situation. By completing go problems, a student can gain some practice in reading out situation and finding the best move, and doing so is considered an essential part of a player's development. It is the easiest way to develop solid fighting skills. For an excellent collection of go problems, head to http://www.goproblems.com/.
As a beginner, my favorite tesuji was the one described in this lesson, which has popped up occasionally in my games (and about half the time, my opponents have failed to notice it). It's very simple, but certainly requires a bit of reading ahead. Many common tesuji are named, and this one is the Crane's Nest tesuji.
Here's the problem:
Black to play and capture at least 3 white stones
The beauty of the correct move in this situation is that it makes perfect sense, but if you only read one or two moves ahead, you might conclude that it doesn't work, abandoning the possibility in favor of a lesser result.
Think about it for a second, then look below. We'll go through the wrong moves before the correct one.
Wrong Move 1
Okay, this is a clear mistake after only two moves. W connects out, and B's chances of capturing anything is negligible. On top of that, the B group is heavy (lots of moves spent doing very little), and that bodes ill for B's chances for victory. Efficiency in Go is essential.
Wrong Move 2
This move is really ambitious, seeking to prevent w from connecting out. It's a good idea, but the play is too far out from B's other stones to be effective. W easily walks out with move 2. To find the correct move, B must discover a way to drive W into his walls.
Correct Move
This is it - the tesuji. to escape, W must either play at "a" or "b", and will be up against B's walls, as we intended. No matter which move W chooses, the three stones should die if B continues correctly.
Bad Follow-up
B must be resolute about sealing W in. Giving way with move 3 is disastrous, and shows the difficulties that a player might encounter if he or she is reluctant to read a situation through.
The Crane's Nest Sequence
This is the way to go. Note that, due to symmetry, W can play move 2 at 4, and there won't be any difference. After move 5, W cannot connect between 2 and 4, because B will capture all seven stones. B will capture at least five stones in this situation, and this heavy group will have come to some use.
In a regular game, this tesuji comes up mainly when W ignores a cut made by B, allowing B to form the Crane's Nest. If W fails to see the tesuji coming up, B will capture the stones using the sequence, and the cut will have worked.
Here's an example: Crane's Nest Example