# One-Space Notchers

Keywords: Life & Death

One-space notchers are groups that consist of a chain on the second line, interrupted by a notch of one empty space on the second line and one stone on the third. The term was invented by James Davies. See also Notchers, Two-Space Notchers and Three-Space Notchers.

The rule for one space notchers is: "Four die, Seven live". You may also remember this as: "Five and Six are unsettled".

Four die

Here's the proof that "Four die". Even if Black plays first, White always has an answer to keep his group dead. Black 1 is answered by White 2 and vice versa.

Seven live

Here's proof that "Seven live". Even if White plays first, Black always has an answer to keep his group alive. The diagram shows one white attack that fails. You can verify for yourself that it doesn't matter where the notch is located. You can also verify that five- and six-space notchers are unsettled, i.e. that the black group is alive if Black plays first and dead if White plays first. If you don't know how to verify unsettled cases, look in the discussion of two space notchers.

### Classification

One-space notchers

Marked points: possible weaknesses
Marked stones: legs

### Classification

See notcher code for the coding.

• All of 111xx, 112xx are dead and not worth discussing
• All of 1xxWW are dead until 133WW. 133WW can make a ko. From 134WW onward it can live by connecting the stone in atari:
134WW

Black lives with 1

### 122

122WN

122WS

can live with 1

122NN

can live with 1

122NS

can live with 1

122SS

can live with 1

All 122 can live, except 122WW and 122WN which are dead

### 123

123WN

Black can make a ko

123NW

Black can make a ko

123WS

Black can live

123NN

Black can live

(...)

123SS

Black can live. White can kill at 1.

All 123 can live, except for 123WW, dead, and, 123WN and 123NW, where Black can make a ko.

### 133

133WN

Black can live at 1 or A. If White later plays the other hane, Black can live by playing at B.

133WS

Black lives. White 1 is the strongest move. Any other move is answered by Black 1.

133NN

Black lives. White 1 is the strongest move. Any other move is answered by Black 1.

(...)

133WW makes ko. 133WN can make life. All other 133xx live

### 116SW

The status of 116SW depends on outside liberties.

116SW

Without outside liberties, kills.

116SW

With a outside liberty, Black lives.

One-Space Notchers last edited by redbear on March 2, 2014 - 19:55