Problem No. 120 from Igo Hatsuyoron
Created by Inoue Dosetsu Inseki (1646 - 1719)

Black to play and win
back to the Introduction


 What this problem is really about. THIS PAGE.

 Highlights (our key-results; highly recommended for a better overview).
 Main Path of the "official" solution in detail.
 Table "Main Path" (summary of the variations of the Main Path).
 Table "The second Throw-in" (summary of the results of our investigations).
 Several questions from 2007 (= the path to the Guzumi).
 Variations of the Main Path in detail.
 Variations after the second Throw-in in detail.
 Research on the move that probably solves the problem.
 TIME - what distinguishes between amateurs and professionals (or joins them together ?).

What this problem is really about

Dia. 01.1: "Igo Hatsuyoron's Hanezeki"

Igo Hatsuyoron's problem is quite complicated. The key issue is the life of the black group at the top - White can stop it getting independent life with 2 Eyes, and Black will have to kill all the white stones in the lower right.

The first 71 moves of the "official" solution serve to construct a special type of Seki, called Hanezeki, which is discussed below. This will be a temporary Seki. The blue (= black) stones are cut off, and the white stones above are part of another (linked) temporary Seki, as is the large black group in the top right, which is eyeless.

So Black must live on the top. To do so he must either get 2 Eyes there or he must force White to capture the 20 black (= dark blue) stones in the centre, leading to the collapse of the (temporary Hane-) Seki, which, in turn, allows Black to capture all White's stones in the lower right, thus saving Black's group at top right.

Black's only chance of forcing White to capture Black's 20 stones in the centre is to attack White's stones on the left, and to reduce them to one Eye (or less). But it's now White's turn. In addition, Black must be aware that it is White's option either to capture the black string in the centre, or to take liberties from the black group in the top right.

If White is willing to let Black get two Eyes at top (maybe 65 is not played in this case), then Black may have to pay a price in the top left corner. But Black will also get a small amount of compensation (about 10 points) in the top right, because most White moves there are no longer Sente for White - indeed many are now Sente for Black, instead.

Dia. 01.2: "A Hanezeki"

The diagrams on the left show a special type of Seki, called "Hanezeki".
(The stones on the right are coloured for the sake of comparison with Igo Hatsuyoron's problem.)

A Hanezeki is a Seki in which

1. each side could capture an equal number of stones internally (here 3 stones, light yellow / light blue), but obviously do not want to do so because they would lose the capturing race if they did so, and

2. there is the further refinement that one side (here White) has the alternative of capturing some "external" stones (here 1 stone, dark blue; may be a Hane, therefore the name of the Seki).
However, if the "external" stones are captured, then the Seki collapses - if there are not many external stones, then it will not be an advantage (for White) to capture them.

Dia. 01.3: "Neither Black nor White Will Win"

On the left we show why neither Black nor White wants to start the capturing race (Semeai).
If Black starts at 1, then he loses after White plays at 6.
If White starts by capturing at 4, then Black steals the eye with the triangled stone, and White loses the fight.
The side that starts here will eventually lose the Semeai by one move.

White cannot safely capture the single "external" black stone with White 1. After Black has stolen White's eye with 6, White will die.
Note that, in this diagram, if the single "external" black stone is replaced by 8, or more, black stones, then White could profit from starting this fight.

Ignoring questions of Sente, in the Igo Hatsuyoron problem, White's capture of 20 stones costs her about 25 points locally.

There is further discussion of hanezeki at Sensei's Library.

return to the top of page

The diagram-pictures were created with "SGF conversion" on Jan van der Steen's
Compiled by Thomas Redecker.

For a blog on East-Asian books on Go, please refer to Tchan001's Blog..

(c) DGoB -  letzte Aktualisierung: 2011-08-22 20:00,