Favorite Moment 6

  Difficulty: Intermediate   Keywords: MiddleGame, Strategy

This favorite moment is an example of using an invasion for creating thickness.

The game is the 4th game of the 50th Kuksu title match played on March 16th 2007 between Yi Ch'ang-ho (black) and Yun Chun-sang (white.) Komi is 6.5.

Table of diagrams
Position at move 59
Counting Black's left side
White starts an invasion
Using the aji of the lower side
White lives
White succeeds with his move
White sets up additional forcing moves
Forcing from the outside
Position at move 100
The final position: White is thick
Rearranging to illustrate White's victory

[Diagram]
Position at move 59  

The position after move #59 is the start of our analysis. Black just played on the left side, expanding his moyo. Moyo, you ask? It sure looks like solid territory to some of us. If we would count the left side as territory then it would look like something below.

[Diagram]
Counting Black's left side  

Let us assume that the final border is on all points marked 'X'. Black will make 31 points on the left side. Evaluating the whole board, one can see that White cannot compete on territory against Black. Therefore, White mounts an invasion into Black's left side.

[Diagram]
White starts an invasion  

White invades at W60. Note that this is exactly on the boundary line we have mapped out in the previous diagram. As such one could also say that W60 is a reduction.

B61 aims at shutting White in. Up to B65 Black succeeds. It seems unlikely that White can make life in this narrow space. Apparently the two white stones are captured and his strategy failed, or did it?

[Diagram]
Using the aji of the lower side  

Switching to Black's other vulnerable spot, White plays W66.

Black has no other choice but again sealing White in with the sequence of B67 and B69.

White W70 seeks life in the corner, but B71 ensures that White is unable to make two eyes.

Far from failing the line of play is exactly working out as White has planned. White W72 and W74 make miai of living at the top or living at the bottom.

[Diagram]
White lives  

If Black tries to save his stone with B1 in this diagram, then White attaches at W2. No matter how hard Black tries afterwards, either the lower white group makes two eyes, or the two black stones get captured. Neither outcome is desirable.

[Diagram]
White succeeds with his move  

Therefore, after W74 Black does not save his single stone in atari and plays at B75 instead. White immediately captures at W76 and Black must connect along the second line with B77. This move is necessary, so that the black stones above do not become an easy target for attack.

Play comes to a temporary pause when Black switches to the top with B79.

[Diagram]
White sets up additional forcing moves  

White seizes the initiative and plays W80. Not so much in a futile attempt to make life for his group, but in order to get some more forcing moves from the outside.

[Diagram]
Forcing from the outside  

White continues his play and Black makes sure that White's groups remain dead. Nevertheless, White is able to get in many favourable forcing moves.

[Diagram]
Position at move 100  

This is the final position for our analysis. White 100 (the marked stone) concludes the sequence.

Let us do some counting again.

[Diagram]
The final position: White is thick  

Black has captured the seven marked white stones and an additional 11 points of territory for a total of 25 points of territory.

White on the other hand has captured a stone at 'a'. Let us assume that the marked black stones are dead. Then White has made 8 points in the process.

Granted, Black got in a move at the top which is worth something as well (around 10 points?). But even this simple counting shows that White is at least not worse off than before.

What clinches the game though, is White's thickness in the center. Have a look at the next diagram.

[Diagram]
Rearranging to illustrate White's victory  

In this diagram we have rearranged the stones in a way, so that Black still has 25 points of territory and White has captured the three stones on the outside. Compare this with the starting position (first diagram at the top of the page).

Do you see how submissively Black has played? Not only was Black unable to hold the territory mapped out in the beginning or is at best even if we account for his marked move at the top.

In exchange for merely turning his moyo into territory White got superior thickness on the outside. This thickness dominates the whole board.

White has a winning position and indeed goes on to win by resignation.


Favorite Moment 6 last edited by Jeff on October 27, 2007 - 00:10
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