Last week, we said sustainable development ...

By Rob Van Zeijst

Last week, we said sustainable development entailed "comfortable efficiency" and signified an absence of overextension and the misapplication of resources. At the same time, insufficient development can create problems. Go is a zero-sum game in which any loss your opponent suffers is your gain. Therefore, forcing your adversary to fail to develop his stones efficiently or to overextend is a viable strategy, because his position may be strong but inefficient or loose and weak.

Extensions

The rule of thumb for developing a lone stone on the third line is a two-space extension. From a more robust formation, you can make a wider extension. So if you can force your opponent to make an extension that is smaller, his position will be underdeveloped and cramped. Let us look at some examples.

Diagram 1: The three black stones on the right form the so-called sanrensei opening, three stones in a row on the star points. This is a good opening to study because the basics are simple. The main idea is to lay out a grand structure and induce your rival to jump inside. Next, you go for the jugular, ideally keeping the initiative and making points during the process. At one stage or another, White usually comes in at 1. Black 2 now has two functions. First, it prevents White from sliding into the corner. Second, it virtually forces White to play at 3. After 4, White must somehow extend and the usual move is to 5. The usual extension from a wall of two stones (1 and 3) would be three spaces, i.e., at A. But the marked black stone forces White to play an "underdeveloped" extension at 5. Therefore, even if the spaces between Black's stones are overextended, even if he invades White cannot make a proper base. In this example, Black successfully forced White to play inefficient moves.

Diagram 2: In this game between Honinbo title defender Cho U (White) and Meijin Norimoto Yoda, White extends to 8 and Black to 9. White then plays at 10, indirectly defending against an invasion by strengthening his stones at 2. However, Black cleverly invades with 11 and 13, and quickly moves out with 15 and 17 to put pressure on white 8 (see Reference 1). Next, White plays 18 through 22 and suddenly this starts looking like an extension from White's lower right, which Black reduces with 23. The 24-25 exchange is interesting as white 24 overextends and induces a narrow black extension to 25, which also serves as a springboard to invade around A. Still this exchange is slightly favorable for White because he wants to play at 26 and 28 as soon as possible. Black goes in to make a huge extension all the way to 29. This makes miai (a situation where Black can always play one of two options) of attacking the corner with B, white C, black D on the one hand, and expanding the right with 30 on the other hand. White 30 prevents the latter while expanding his own framework and defending against an invasion around A.

Reference 1: Black 1 is an unimaginative invasion. White plays 2 before jumping to 4. Black's stones come under heavy attack. Instead of 4, White A is also a good move. This aims at the sequence white B, black C, white D and black E. A corner invasion is eliminated with white F.

Solutions to last week's problems

Solution 1: If Black invades at 1, White must play at 2 to prevent the invader from making a base. Black 3 does the same, but White is now the first to move into the center with the sequence through 8. This is very severe for Black. Instead of 4, White can also play at A, followed by black 7, white B, black C, white D. In both cases, White has the initiative.

Reference 2: After black 1, White's move to 2 is too passive. Black extends to 3 and White needs to defend the corner with 4 and 6. Black now can seize the initiative in the center.

Solution 2: White 1 is the normal move in this situation. It makes miai of extending to A or B, or to 3 and C, for that matter. If Black approaches from 2, White extends to 3 or B and vice versa. Therefore, whatever happens, White can always make a base.

Reference 3: White 1 is another possibility. However, Black will probably pincer around 2. The sequence through 11 is the most natural variation, but Black gets sente (free to play elsewhere) to play at 12. Now the marked stones form one large framework. This is not necessarily bad for White, but it is a simpler situation for Black.

Problem

Problem 1: In this game between two top players, White has just extended to 26. Why not simply make a two-space extension? Where do you think Black will move next?

Van Zeijst is a four-time European go champion and European representative at the Fujitsu World Championship.