© 2015 Slate & Shell

Reductions

Making and Defending Against Reductions of Common Positions

Iwamoto Kaoru 9 dan

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Originally published in Japanese by the Nihon Ki-in

Translated by T. Ogoshi with assistance from Roger A. Newlander and initially published in the American Go Journal.

The permission of the Nihon Ki-in for the continued use of this material for the promotion and development of go in the West is greatly appreciated. It was initially translated by T. Ogoshi with the assistance of Roger A. Newlander and edited by Don Wiener for publication in the American Go Journal in the 1980’s. It was then re-edited and republished by Slate & Shell as part of Keshi and Uchikomi: Reduction and Invasion in Go which has been out of print for several years. The section on reducing has again been re-edited for this publication with substantial reworking of both the diagrams and the text, correcting some errors. A new edition of the material on invasions was published earlier.

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Introduction

“Reduction”, keshi in Japanese, involves pressing against an opponent’s formation in order to reduce the size of a large potential territory. The aim of reduction is different from that of invasion. Reduction seeks to contain the opponent while maintaining pressure on the opponent’s position from the outside while invasion seeks to destroy the opponent’s potential territory by playing inside it. Through the process of reduction, the opponent may stabilize some territory but the player who is reducing will gain a position on the outside.

It is important to determine whether invasion or reduction is the proper tactic in particular cases. Reduction is appropriate in situations where the strength of the opponent’s position makes an invasion too dangerous. When invading stones are captured, the opponent usually also gets outside strength. In other cases, the invader may end up with a weak running group.

Iwamoto Kaoru

Copyright Page

© 2015 Slate & Shell

All rights reserved. Reproduction in whole or in part is prohibited.

Slate & Shell
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Edited by William Cobb and Richard Hunter

Cover design by Laurie M. Crammond

Conversion to SmartGo Books by William Cobb and Richard Hunter

ISBN of print edition:
1–932001–70–0

Table of Contents

Reductions: Making and Defending Against Reductions of Common Positions

Introduction

Copyright Page

The chapters in gray are included only in the full book.

Formation 1

Formation 2

Formation 3

Formation 4

Formation 5

Formation 6

Formation 7

Formation 8

Formation 9

Formation 10

Formation 11

Formation 12

Formation 13

Formation 14

Formation 15

Formation 16

Formation 17

Formation 18

Formation 19

Formation 20

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Formation 1

Formation 1

This powerful black formation, based on a corner enclosure, is too strong to risk a deep invasion. It is the largest position of this kind likely to occur in an actual game. So the opponent’s task in this case is to seek the best threats and pressures from the outside, that is, reduction rather than invasion.

Diagram 1

＞＜ ▶︎

Consider this example of an invasion by White. Obviously, White has gained some benefit in the corner, but this is small compared to the huge territory that has been solidified by Black 14. Even though White manages to live in the corner, White has actually helped Black in a significant way. White would be better off reducing Black in return for outside influence. In this case, Black 2 at 10 would also give Black an excellent result.

Diagram 2

＞＜ ▶︎

Black could also attach to White’s deep invasion with Black 2, completely blocking White from penetrating the corner. It would be better for White to feint against the black territory instead of trying this deep invasion.

Diagram 3

＞＜ ▶︎

Starting with the lighter move of this White 1 instead of a deep invasion is a better strategy for White. This tactic takes advantage of the width of Black’s position. This is a common reduction technique. See the following diagrams.

Diagram 4

＞＜ ▶︎

After White 5, Black can secure the corner by cutting at 6 (see Diagram 6 for an alternative). White forces with 7 and Black responds with 8. (The 7–8 exchange here is a similar forcing technique to the 1–2 exchange in Diagram 3.) White 9 threatens to capture a stone, which Black prevents with 10.

Diagram 5

＞＜ ▶︎

White properly abandons the two white stones on the upper right edge: trying to save them would be very risky, although White 11 does threaten to link to them. Black prevents that with 12, making a nice territory and preventing the isolation of the three black stones in the middle of the right side. White is satisfied to prevent an expansion of Black’s territory and reduce Black’s potential for outside influence. White’s forcing moves press Black inward and develop White’s own outside potential.

Diagram 6

＞＜ ▶︎

Black can play 6 in this way. White should then jump lightly to 7. White could live in the corner (see Diagram 8 below), but first makes sure of the outside situation with 7, which is more important, that is, bigger, than gaining the points in the corner. Black would happily trade the corner for developing in the center, starting around A. White’s strategy has been effective. If Black plays in the center after White 7, White will take the corner.

Diagram 7

＞＜ ▶︎

Black might play 4 this way (instead of 4 at 5 as in Diagram 3), trying to keep White in the corner in return for getting an outside position. After Black 6, White should switch to 7 to counter the increased strength of Black’s right side. White could use 7 at A to take the corner, but Black would build outside strength with Black B. After White 7, the situation is not good for Black, who must now take the corner or lose both it and outside potential, suffering both an invasion and a reduction.

Diagram 8

＞＜ ▶︎

If Black ignores the corner situation after Diagram 6, White could play 9, and after Black 10, White 11. This could be followed by Black A, White B, Black C, and White D. Alternatively, instead of starting at A, Black could play C, White F, Black A, White G. In any event, White lives in the corner.

The key thing to remember in this sort of situation is that the outside is more valuable than the corner for both players.

Diagram 9

＞＜ ▶︎

After Diagram 8, White should not exchange for later because of the ko shown in Diagram 9.

Instead, White could prepare by playing White 1 or White 5 here in gote with the option, perhaps, of later playing at .

Diagram 10

＞＜ ▶︎

So do not make a mistake and think you get more points by establishing the position in Diagram 10. Be careful to watch for ko possibilities!