Invasion of third line three space extension
Standard replies to 3 space extension invasion
bobulatorm: a, b and c are all standard responses, depending on surrounding board positions. b is a strong attack when B has supporting forces nearby. c is a slightly weaker attack, and a is only to be played as a purely defensive attatchment.
Lower attachment
Icepick: The most common response I see (as a DDK) is a.
can be on either side, depending on the rest of the context. At this point, Black can either draw back at a, or cut at b.
Peaceful, but Black is separated
HolIgor: This variation is considered bad for Black as one of the black stones remains in a silly position.
dnerra: I would like to support HolIgor's point very strongly. This is result is a big disaster (in fact, so big, that I almost used all-caps...) for Black, unless he wanted to sacrifice the stone on the right from the very beginning.
White can now cut back at a or draw out at b.
dnerra The cut is only possible if there is help from nearby stones.
Black sacrifices to get outside influence, while White gets some territory.
Velobici: This line of play appears to be horrible for Black. Black started with a two stone to one stone advantage. Black has sacrificed four stones. White is out to the left with a nice position. The White cut at a remains a danger for Black.
HolIgor: Acceptable. Usually and
are not played. They are ko-threats. White's aji is not good. The roots of the problem are in the previous moves. How did it happen that Black had a hole in the middle? Why did Black choose to play on the second line instead of jumping out and starting a running fight? Everything depends on the environment. There are situations where this line of play is OK for Black. Black gets compensation in the form of outside influence.
dnerra This diagram leaves me very confused. I cannot come up with any surrounding conditions where this sequence makes sense. I think the author of it may have mixed it up with the following sequence, which is sometimes correct:
Here the point of adding
and
to the sacrifice is that additionally to
, also B0 becomes sente.
dnerra:
is usually played at
.
Diagonal attack
diagonal attack attempts:
still black needs to defend at a
or
Weaker attack