Three-space extension

  Difficulty: Beginner   Keywords: Opening

Compared with two-space extension

[Diagram]

Example: Three-space extension on the third line

Compared with the two-space extension, the three-space extension has two advantages, which can be explained using go concepts, and one clear disadvantage.

[Diagram]

White can invade

To start with the disadvantage. White can invade at W1 here, and (unlike the case of the two-space extension) Black cannot force a connection by immediate means. What Black usually does is to jump out, for example at a, enlarging the scale of the struggle; or to play at b (possibly leading to a later sacrifice), to make the most of tactics locally. Therefore this length of extension isn't easily handled in all positions.

[Diagram]

Advantage 1: not over-concentrated

One major reason to choose to play the three-space extension can be seen in this sequence. If White is about to play the diagonal attachment at W1, Black's marked stone ends up on an ideal point after the proper answer B2 (see extension from a wall). One line closer is over-concentrated, that is, worse, from the point of view of good development.

[Diagram]

Advantage 2: light

The second possible advantage is if Black is seeking to play lightly - stay out of trouble.[1] This type of sequence is appropriate if White is strong in the upper right, as here. In that case Black a, White b might be good for White, and Black is better allowing W1 in return for B2.

[Diagram]

Variation

Here Black can be quite happy with his development.



In some contexts completing the shape with Black at a (instead of jumping out at B2) might be better.

Charles Matthews


List of basic types

[Diagram]

Three-space extension on the third line


[Diagram]

Three-space extension on the fourth line


[Diagram]

Mixed three-space extension


[Diagram]

Three-space extension from a wall

See Extension from a wall

There are pages dealing with invasions in these extensions on the three-space extension invasions path.


[1]

[Diagram]

Advantage 2: light

B2, approaching White's wall, is problematic, while extending only to a instead of BC allows White to play at b.

[Diagram]

Prepare the way

B1 - B3 press against WC, preparing for a safe extension to B5. This sequence avoids the problems of an immediate extension.

--Bill Spight



Charles This idea of Bill's, to use the 3-5 point low approach, press, is a bit more subtle than may seem at first glance. For example, B5 is held back one line, giving White much less chance of fighting on this side.


This is a copy of the living page "Three-space extension" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.
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