Life In 19x19

emeraldemon wrote:Not exactly the same, but I've been thinking about & researching extensions from and against the 3-4 enclosure.

With the 4-4 stone at least, the extension is where it is because if white invades at the 3-3, the resulting wall for black will be perfectly distanced from the extension. If white invades with an inside approach move, black can force white to overconcentrate (that is, the extension stone acts as a ready-made pincer). Further away and it wouldn't act as a pincer. eg:
Which means that on a huge board, I'll bet when you extend from a 4-4 stone, you don't chose the middle of a side, but chose the 7 point jump from the corner (the middle of a side is more like forming a vast moyo ie: something like niren-sei).

Not sure about the 3-4, but I bet it follows similar logic. It's not about forming the largest moyo possible (if it was, you'd approach the far corner it's facing). It's not about securing territory (if it was you'd make a tighter extension). It's about forming the largest area with a pre-existing pincer stone that will make white reluctant to invade, because he'll be concerned about becoming overconcentrated so early in the fuseki, or just helping black form secure territory. And if you expand to the other side and reinforce both wings, you've just about got a huge solid territory moyo that covers about an 8th of the board for the cost of only 6-7 stones.

Toge: As white, I tend to just take O17 and try to match moyo for moyo. I feel that the bottom right isn't urgent yet, because white still has options on either side that can be considred close enough to miai. That said, it's still iffy of whether or not white can build a moyo as efficiently as black, given black's 'head start'. I'd be eager to hear more opinions though, as you're higher-ranked than I am and I'm sure you knew everything I'm saying before you posed the question.

Numsgil wrote:So I spent the weekend re-reading Wilcox's sector fights, where he spends a lot of effort talking about walls. I think I can make this a bit more productive of a conversation by helping to define some terms a little better. I'm going to present this information as authoritative, but it really only represents my novice understanding

Anyway, there are three kinds of plays that might be thought of as extensions:
1. Extension to form eye space (AKA safety extension)

2. Extensions to form a moyo

3. Extensions which attack

4. Useless wall

Bill Spight wrote: 1. Extension to form eye space (AKA safety extension)

$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O X . . . 1 . . . . . . . . . . . |
$$ | . . O X . . . . . , . . . . . , . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . 2 . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |

Click Here To Show Diagram Code

[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O X . . . 1 . . . . . . . . . . . |
$$ | . . O X . . . . . , . . . . . , . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . 2 . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |[/go]

You may also see a closer extension, so that does not become sente.

Can you expand on this? I've seen this idea in a joseki before, too, where a variation has the extension made a bit closer to ward of future forcing moves against the group. What specific threat makes the move locally sente (I assume separating the wall and its extension)? And more importantly, what about moving closer to the wall prevents this from being sente?

2. Extensions to form a moyo

$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . . . . . 3 . . . |
$$ | . . O X . X . . . . . . . 1 . . 4 . . |
$$ | . . O X . . . . . , . 5 . . . O . . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . O X . . . . . . . . . . . . . 2 . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |

Click Here To Show Diagram Code

[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . . . . . 3 . . . |
$$ | . . O X . X . . . . . . . 1 . . 4 . . |
$$ | . . O X . . . . . , . 5 . . . O . . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . O X . . . . . . . . . . . . . 2 . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |[/go]

is an extension from the top right corner. It may also be considered an extension from the Black wall. is too far away to be considered an extension from the wall (more than 5 spaces).

What does "more than 5 spaces" mean? More than 5 spaces from what? If it refers to a rule or proverb it's not one I've ever heard, so I'm interested.

4. Useless wall

$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . b . . . . . . . |
$$ | . . O X . X . . W . . W . a W . . . . |
$$ | . . O X . . . . . , . . . . . , O . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |

Click Here To Show Diagram Code

[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . b . . . . . . . |
$$ | . . O X . X . . W . . W . a W . . . . |
$$ | . . O X . . . . . , . . . . . , O . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |[/go]

OC, Black would rather that the wall be flipped 90 degrees. However, the wall is far from useless, and, supposing that it were complete before the marked stones were played, Black can almost certainly be satisfied (unless she has made a mistake elsewhere). And White's ji-moyo (almost territory) is still invadible. (There are several places to start. I do not know what is best, but my inclination would be to probe at "a". "b" is also a thought. )

Yes, if the white stones had to play low to approach black's thickness after it was built, black's thickness has at least partially payed for itself by passively limiting white's growth. Every approach would be gote and not super big.

As far as invading, I look at this and it might as well be a solid line of white stones. There are some maybe 3-4 point gote plays I see, but that will tend to wait until the late end-game before being made. Maybe there's a sequence I'm not familiar with?

Numsgil wrote:

Bill Spight wrote: 1. Extension to form eye space (AKA safety extension)

$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O X . . . 1 . . . . . . . . . . . |
$$ | . . O X . . . . . , . . . . . , . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . 2 . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |

Click Here To Show Diagram Code

[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O X . . . 1 . . . . . . . . . . . |
$$ | . . O X . . . . . , . . . . . , . . . |
$$ | . . O X . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . 2 . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |[/go]

You may also see a closer extension, so that does not become sente.

Can you expand on this?

Black's sagari makes this better for Black than the joseki, but I think that is still a good play. As always, no guarantee of correctness.

What does "more than 5 spaces" mean? More than 5 spaces from what? If it refers to a rule or proverb it's not one I've ever heard, so I'm interested.

If you leave 6 spaces between your stones, then your opponent has room to invade and then, if not pincered, to make a 2 space extension. Playing that far away from your existing stone or stones may be a large play, but we do not call it an extension.

4. Useless wall

$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . b . . . . . . . |
$$ | . . O X . X . . W . . W . a W . . . . |
$$ | . . O X . . . . . , . . . . . , O . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |

Click Here To Show Diagram Code

[go]$$B
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O O X . . . . . . b . . . . . . . |
$$ | . . O X . X . . W . . W . a W . . . . |
$$ | . . O X . . . . . , . . . . . , O . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . O X . . . . . . . . . . . . . . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |[/go]

OC, Black would rather that the wall be flipped 90 degrees. However, the wall is far from useless, and, supposing that it were complete before the marked stones were played, Black can almost certainly be satisfied (unless she has made a mistake elsewhere). And White's ji-moyo (almost territory) is still invadible. (There are several places to start. I do not know what is best, but my inclination would be to probe at "a". "b" is also a thought. )

As far as invading, I look at this and it might as well be a solid line of white stones. There are some maybe 3-4 point gote plays I see, but that will tend to wait until the late end-game before being made. Maybe there's a sequence I'm not familiar with?

I now think that is good. The position is rather complicated, and I have shown several variations. Some of the errors are intentional. But probably not all of them.

Anyway, perhaps such positions won't look so solid anymore.

Another game from 1930.

Bill Spight wrote:what about extensions from walls in general?

My book (p. 233+) gives this general principle for the gap between wall and extension: "First determine the farthest extension that is also a connection, which might be direct or indirect. This must be verified by reading. Then consider also alternatives."

If a wall is strong enough, it does not need an extension. But if you do not extend, how do you make use of it?

It depends on the global positional context. Possible usages include:
- Extend later.
- Build more walls later to create moyo / territory.
- Attack opposing stones while exposing them to the wall.
- Watch while the opponent defends more timidly than without the wall's presence.

Often pros make extensions that are longer than the proverb says. What is going on there?

Suppose they have an implicit understanding of my principle. Then obviously there must be additional reason for playing a not connected extension, e.g.,

- Building a moyo.
- Inviting an invasion.
- Playing a multi-purpose move with also other global relations besides the relation to the wall.

What about extending from weak walls, or walls with defects?

Apply my principle (unless you want to sacrifice the wall (temporarily).

Or do you not extend, but repair the defect?

It depends on the kind of the defect. If its defense also creates (very) thick shape, then defense might be better. E.g., transforming a cutting point into one's own hanging connection might be such a case.