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Chapter Ten. Extensions and Invasion Points

10.1 The two-point extension is stable

This extension with a two-point gap is the fundamental building block for play on the sides. Much of the ordinary reasoning about finding a base for groups in the opening centres on extending in this way.

Of all the ways to construct a two-stone group on the side, this one is the most stable. We shall see in the rest of this chapter how each of the other members of the family of common extensions has some drawback.

That by no means says that the two-point extension is the only shape you need to know. In some cases you can play low moves, with an eye to getting immediate life. On other occasions overall strategy dictates the use of plays on the fourth line, climbing quickly to pivotal or focal points.

The feature that we bring out in this chapter is the existence of invasion points, vital points of shape where an invasion is possible (or may become possible later). There is some discussion in 13.7 of the question of whether such invasions in small spaces are worthwhile.

The two-point extension is not exempt from attack itself. We consider this topic in Chapter 11.

10.2 The three-point extension

The three-point extension on the third line is useful in this sort of situation. Black builds a secure group.

Considered on its own, the three-point extension is a light shape, that is, one that may be defended by sacrificial means. There is an invasion point at A. (Right) Depending on the context, Black can usually cope this way, giving up one stone.

In professional go, the sequence at the top of the page would be thought to lack severity by White. Instead one expects to see White invade at once, and then give up the invasion stone for the moment, as here. It has very good chances of later revival, unless Black plays once more to suppress it.

10.3 On the third and fourth lines

In strategic terms (left), Black 3 has the meaning of making the plays at the ‘x’ points less important. That is, it works against central strategy. Considered in isolation, the shape has an invasion point at A.

When the marked White stone is present, it is normally possible to invade. The tactics can be difficult. (Right) This way is simple, but Black loses territory with little in return.

(Left) If Black resists at 4, the fight becomes complex, with White having to take into account eye space (play at B) and the cuts C and D. (Right) Black may also try 2 and 4. White can escape with 5 and 7, but must worry about the timing.

In contrast, Black 3 here leaves Black a good play at A, and White one at B. In a game of large-scale frameworks both players would be keen to play in this focal area. (Right) White can invade at C, or play contact at D.

White can get a good result invading on the third line, if both these ladders are favourable. As in 5.3, if Black 4 is at 5 White gets good shape. When White starts at 3, Black 4, White 1, we can have the same results.

An example of shape-based thinking in a large-scale position. Black has ignored a focal play by White. White 1 here prevents Black’s connection at A (cf. 2.1). Black can make a 3-3 invasion in the top left corner, to handle that local situation. However White will develop a very solid position, and Black’s influence over the top side will be much diminished. White can have confidence in future fighting.

10.4 On the second and third lines

You can say that a play on the second line early in the game always has some strategic purpose, to compensate for its low position. Here Black 1 is a ‘mole’ play (6.2), trying to live in a White framework. (Right) A marks the normal invasion point in this shape.

This is an opening pattern with efficient shape for both sides. (Right) White can take a profit by invading here later; but Black ends up strengthened.

This is one idea for invading White’s framework, set up in the revised or high Chinese opening style. There is room for Black to extend to 3. The resulting position is complex; White has plays at A, B or C to consider. Why would Black play this way? With another play at B, Black is settled. But White may intervene, a point already made in 2.3.

There are these potential ko fights (both of them examples of the ko lock idea from Chapter 5). These are big fights, and hard to judge.

There is also this attack for White. Up to 10 Black has lived, and also avoided being shut in.

Black would probably not die without Black 10 of the last diagram. But it is still important to play it, to retain access to the centre and preserve a big endgame play in the corner at A. (Left) Unreasonable for White to cut Black now the marked stone is played. (Right) The immediate clamp play White 1 is too simple-minded to kill Black (cf. 2.6), and is a loss. Black could play as shown, cutting at 4 to set up a liberty shortage, or hold back 2 and 4 for later, since Black 2 here is normally worse in endgame terms than jumping in to 3. But Black cannot rely on White attacking so bluntly: White will wait for an inconvenient moment.

10.5 On the fourth line

When a game is being played on a very large scale, one sees fourth line plays such as 1, to be followed up by 3 at a key point. In this case Black is thinking more about central development than points on the top side.

Playing 3 and so on before jumping to 7 is big, but there is some risk that White will play at A rather than 6, a plan tried out by top pros.

{{Dia 697}} {{Dia 698}} (Left) If Black jumps to 3 immediately White could play 4 and 6, to which Black has no very good answer (connecting at 8 is overconcentrated). If Black plays away with 7, White can cut at 8. Black 9 looks to sacrifice Black 5 to build up outer strength. (Right) A rare example (in this book, rather than in games) of playing into very bad shape. Black 9 is terrible. Black gains only a weak group.

The three-point extension (left) may be invaded at A or B. It is a loose extension, so that unless Black is strong locally, these invasions probably live. (Right) There is no definite invasion point in the two-space extension on the fourth line. However it doesn’t hold any territory firmly.

On the top side, Black 1 and 3 may suggest themselves. White 4, sooner or later, is a focal point. The normal way of thinking for Black is to hold back, with 3 not A. If Black 3 were at A, White 4 would have more effect on Black; the invasions suggested above would be more severe.

It has to be understood that Black is aiming for influence first, in placing two stones on the fourth line. The number of possible later tactical sequences, such as these, is quite large. Adding to the discussion in 10.1: we can say in this case the Black formation on the fourth line isn’t inherently stable.

10.6 The threat of connecting out

The tactical ideas from this chapter apply in many more situations, some of which need to be studied in depth. White 1 here is on a key point for invasion, and White A or B will follow.

In this case the marked White stone makes the invasion at 1 possible. After 2 there are set sequences for White. But the priority is to identify White 1 as a vital point, threatening to connect out to the left.

Two further common examples of vital points. (Left) White 1 is based on the double threat of A or B to connect out. (Right) Not really in contradiction with the proverb in 7.7 on how to peep, since here White 3 connecting under after Black 2 is big. Black does have other options (Black 2 connects solidly, or at 3 to squeeze once cut, for example).

Chapter Ten. Extensions and Invasion Points#

10.1 The two-point extension is stable#

10.2 The three-point extension#

10.3 On the third and fourth lines#

10.4 On the second and third lines#

10.5 On the fourth line#

10.6 The threat of connecting out#