Gokyo Shumyo, Section 1, Problem 56 / Solution

Main line  

The first move is probably the hardest one. Why not 2-2 or 4-2 ? We'll investigate that later.

Reference diagram  

White can enter Black's EyeSpace from two sides: at a or b. Black has to find a move which protects against both. Let's analyze some failures first.

Failure 1  

Simply closing off at 1 is not good. White 8 makes miai of a and b.

Failure 2  

If Black closes off the other side, White breaks in from the first. Up to 10, Black makes a (slightly modified) door group which is dead.

Other candidates  

Here a and b also fail to protect against White 2. So let's investigate the last candidate, c.

Failure 3  

Black 1 fails to protect against the jump to 2. His eye space is sufficiently reduced. The rest of the moves are for reference.

Variation 1  

If White plays 2 or a, Black protects at 3 and makes such nice shape that it isn't even necessary for Black to respond to White 4. We'll analyze this in Gokyo Shumyo, Section 1, Derived Problem 56.