Small gaps
The small gap is a particular feature of double-figure kyu players' games, which stronger players instinctively avoid in most cases. It usually arises from some kind of play that is too close.
Here's a typical sequence, in which Black is not doing at all well. There are several reasons for that. But look first at the result.
Concentrate on the two stones. They are separated only by a diagonal jump; and yet
cuts the communication between them extremely effectively.
This kind of play, with , is rarely effective because White can make so many cutting points in Black's formation with the plays at a and b. After
creating further chances at c and d, it is unlikely that Black would kill White in a handicap game: too many possibilities for White.
Playing here is the kind of play that in fact makes it easier for Black to attack successfully. If White a Black can choose b or c: in either case the fact that
is one line further away is helpful to Black.
If on the other hand Black doesn't understand the basic principle and plays and
, White will be able to cut. Black should be able to think of playing
at a instead.
This, for example, is an unreasonable fight for Black since White at a is now strong.
Another way to get the feeling that Black has effectively forced White out through a small gap, is to consider this re-ordered sequence (tewari). In this case (a raw peep), and the bad exchange
/
, are exactly doing that.
Bill: Just to add to that last paragraph, dividing your opponent's forces is strong (unless they are already strong). On top of that, the smaller the gap through which you push, the stronger the push that divides them. The basic reason for that is that it is easier for them to connect if you do not separate them. The driving tesuji makes use of this idea.
Discussion of initial sequence
If Black wants to attack the white stone, he should prefer to stay a bit further away from it. (separating the two white stones) or Black a (attaching against the stone one is 'not' attacking) are better ways to go about this.
Another alternative is to exchange for
to reduce white's options in the corner, and then splitting. However, White still has the option of invading at b in an attempt to sacrifice her two stones at the top.[1]
If Black does play , go logic calls for Black to cut at
next. The resulting fight is hard for both, but more so for White, so probably White has to give way by playing
at
, allowing Black to play at
and make a thick wall. - Andre Engels
[1] There is a modern joseki here.
Without the black stones nearby, up to has become a joseki (post-Ishida). I haven't seen this in a book, just the variation with
at
to take central influence.
The interesting thing here, of course, is that seems to contradict directly what is said earlier on this page.
Naturally there is a reason for this, in pro play. Black most often continues by capturing at a (honte) removing a possible shortage of liberties. Then White can play at b.