Three-Space Notchers

    Keywords: Life & Death

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


[Diagram]

Three-space notcher

The rule for a three space notcher is either "Four die, Six live" or "Five is unsettled". Verify for yourself that Black can live and White can kill by playing at a in the diagram. For this reason a is called the vital point of this formation.


Classification

[Diagram]

Three-space notchers

Marked points: weaknesses
Marked stones: legs


Classification

See notchers for the coding.

311

[Diagram]

311NN

Even if Black takes the vital point at 1, White first destroys eyeshape, then makes miai of a and b. With one of his weak spots occupied by White, the black group's eyespace is almost filled with three in a row.


Hence 311WW, 311WN and 311WS are also dead


[Diagram]

311NS

Black 1 makes life.

[Diagram]

311SS

Black still needs to play at 1 to make life.


311 is dead, except for 311NS and 311SS, which can live


This is a copy of the living page "Three-Space Notchers" at Sensei's Library.
(OC) 2016 the Authors, published under the OpenContent License V1.0.
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