Reduction

   

Chinese: 淺消 (qian3 xiao1)
Japanese: 消し (keshi)
Korean: 삭감

Reduction means playing a move outside or on the apparent boundary (see sector line) of the opponent's framework. The Japanese term keshi has a broader use. For example, thickness can be erased[1].

In contrast with a deeper invasion, the idea is gently to reduce the size of the opponent's framework, limiting it to a manageable number of points, by playing near the edge of it.

In that sense it is less ambitious than an outright invasion, which may involve playing right in the heart of the framework in the search for eye space. However reduction is often less risky than an invasion, allowing the reducing group to run away in good order; and it can be just as effective.

In the case of a large scale framework, the correct point from which to reduce it is often in the center of the imaginary line across the framework's open side (aka sector line). The opponent will either protect from the inside direction, in which case the reduction has succeeded, or attack from the outside with a move such as a cap, in which case a jump further into the framework from the initial reducing stone will create the beginnings of a living shape.

Proverbs about reduction

There are some proverbs referring to reduction, such as

SL Pages on standard reduction techniques


Footnotes

[1] Bob Myers: Of course one can refer to erasing influence, but this is the use of the term keshi or (more likely kesu) in its everyday sense, not the technical sense of reduction, which is used exclusively with regard to frameworks.

Bill: Offhand, I do not recall seeing keshi used in the sense of erasing influence in the go literature. Can we delete those two sentences?

(Later.) I just did a search using both infoseek and google of Japanese web pages containing both "kesu" and "atsumi". I found about 120 pages, mostly not about go. On the go pages I did not find both words in the same sentence.


In my own games I systematically underestimate the value of reduction, and I go for risky invasions far too often. I guess I need to become more patient :-)

--Stefan


Andy: I've watched a lot of IGS games between high-dan amateurs and I almost never see the classic reduction moves being played. Instead, I see all-out invasions evolving into large complicated fights. Does anyone still believe that Keshi is worth as much as an invasion? Do the pros still believe in reduction?

Bob McGuigan: Of course the proverb is to be taken with a grain of salt. It does not mean that there is always an erasing move that is just as good as the invasion being considered. It is just intended to indicate that keshi should be considered more often. In fact, many high dan players in server go just invade and fight rather than reduce because reduction often requires delicate strategic and positional judgment, which require time to think. I am sure you would find a lot of reducing moves in pro games. Another thing, I think the description of reducing moves above is too restrictive. Fujisawa Shuko's book Reducing Territorial Frameworks has a lot of good information. In particular it implies that a shallow invasion could be a reducing move. And I think the knight's move cap is often characterized as a reducing move, even though it may be well inside sector lines for a moyo. So some reducing moves might look like or even be invasions of a sort. Something not mentioned above is that deep invasions usually end in gote for the invader while reducing operations usually end in sente for the reducer.


This is a copy of the living page "Reduction" at Sensei's Library.
(OC) 2005 the Authors, published under the OpenContent License V1.0.
[Welcome to Sensei's Library!]
StartingPoints
ReferenceSection
About