British Go Journal No. 9.  October 1969. Page 10.
Kaku Takagawa, 9p
Continued from part 3a on page 8 .
Diagram 42 |
Most readers are well aware of the principle of 'two stones - three points' pertaining to extensions along the third line. See, for example, the Vital Points of Go by Kaku Takagawa. In Dia 42, 5 follows this rule.
Similarly, if there are three stones in a wall, a four-point extension can be made. (See BGJ 002: Raising your strength  for further discussion of the defence of these extensions.)
Stones do not necessarily have to be placed one on top of another to use this rule. They can merely be connected in such a way as to give the greatest strength, as will be explained below.
The two-point extensions may not perfect but they are at least safe. There is no danger of a stone being placed between them and cutting them off from one another. If a player makes a three-point extension, there is room for invading between the two stones; but if there are two stones placed together on one side to form a wall, this extension is then also solid.
Diagram 43 |
In Dia 43, we see the maximum extension of five points. This does not imply that a particular extension of three or four points is always proper, nor does it mean that one always extends to the maximum. Often one side makes an expansion of three points even though there is room for a five-point extension. Here there is room on either side to place two-point extensions later so as to be able to consolidate the formations. Although an approach to the white corner would not have the same attacking value as in the case where the marked white stone were at A, yet it still tends to consolidate the black lines. This would be especially true If White should place a stone between 1 and the black marked stone. Then, although both halves of the formation were separate, they would be able to exist independently.
Diagram 44 |
1 of Dia 44 is a four-point extension leaving room for a later two-point jump approach attacking the White corner.
Diagram 45 |
Dia 45 is taken from an actual match game. Apart from the unusual shape in the upper left, we see that 1 has room to make a two-point extension to either right or left. This stone is occupying a large placement point and is entirely different from the case where a solid extension is needed, as on the lower side. If black had followed this solid pattern too early, then his potential area would be greatly decreased. This should be clearly borne in mind.
Diagram 46 |
In Dia 46, White plays a five point extension; after 3, 4 is
necessary to defend his expansion. On the other hand, If 2 had been at
A, a four point extension, no direct reply to 3 would be needed.
[ But A is a three point extension!? ]
Diagram 47 ||
Diagram 48 |
The forms shown in Dias 47 and 48 are well-known joseki. In the first case, White makes a three-point extension by virtue of the strength around 3, and finally Black plays at A. But in Dia 48, white makes a maximum five-point extension, based on the potential strength of the left side due to possible white plays at 6 or A. If Black plays 6, however, then White must follow with 7 as this potential has ceased to exist. Of course, if Black plays elsewhere, White can also delay this defence.
Diagram 49 |
In the joseki of Dia 49, White is justified in extending three points by the two stones 3 and 5. This idea can be further complicated by further advanced strategy as shown in Dia 50.
Diagram 50 |
[ BGJ had Dia 50 other way up. ]
Here the joseki is changed by White for a specific purpose. One purpose for which this would be correct is if there were a Black stone at A and a White one at B. Then this three-point extension also pincers the Black stone at A.
Diagram 51 |
[ BGJ omitted 'B'. ]
The joseki of Dia 51 creates a three-stone wall, allowing White to extend four points. The only drawback here in theory is that, if Black plays at A, there would be a danger of invasion at B. (If White defends against this, Black is ready for a big expansion on the right side.) Thus, in order to check this possibility, White often resorts to only three-point extensions.
Diagram 52 |
Notice that this would be foolish in the case of Dia 52, where a
three-point extension would enable Black to consolidate the top
side* with a two-point jump.
* [ BGJ had 'right side'. ]
Diagram 53 |
[ BGJ omitted 'A'. ]
In Dia 53 is shown a very important handicap joseki - the tsukenobi - where the extension should be five points to 8. This is true because of the power in the upper area considered equal to four stones. Playing 8 at A would not be good for Black; if he wished to play here, he did not have to play 2 at all, but could have played at A immediately after 1. Of course he added to his position with 2, 4 and 6, but White 3 and 5 in combination with 7 are very strong. Black's position is overstrengthened and heavy if he plays at A.
Diagram 54 |
Dia 54 illustrates where it would be bad policy to play this joseki, since the space left for Black's extension to the left is too narrow. Instead, it would be better for Black to play 1' at 4 or 3. Another example of a good extension is shown by White on the left side of this Dia.
Continued in part 4 on BGJ 10 page 11 .