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Before discussing more technique and strategy, we have to introduce some new concepts.
Sometimes, for strategic reasons, we deliberately have a stone, or a few stones, captured by the opponent. Such a maneuver is called sacrifice. The difference with an ordinary capture lies in the intention. Of course, sacrificing a group so large that you lose the game, is a bad strategy. Anyway, the concept of sacrifice is implemented by a few techniques, but has a definite strategic flavour. In the light of sacrifice, there are two kinds of groups: light groups and heavy groups.
A light group is a group that you are happy to sacrifice. The loss doesn't amount to many stones, and the sequence leading to capture will have considerable positive side effects. The group does not fulfill functions that cannot be taken over by other stones.
A heavy group is a group that you are unwilling to sacrifice but have difficulty securing. A heavy group cannot be strong, by definition, and is mostly a large one, or it fulfills functions that cannot be taken over by other stones. The sequence leading to its security has considerable negative side effects.
When one or more stones are killed in a local fight but they are not captured yet, moves in the neighbourhood or even far away, can threaten to bring these stones back to life. This property of killed stones is called their lingering potential.
More in general lingering potential is the set of all possibilities remaining in a position, when a local fight has come to rest. There is no urgent move left, but the position is not completely void of defects either.
The threat to connect or save lost stones, to cut or to kill safe stones, cannot be carried out immediately, but remains as a possibility that can be exploited at the appropriate moment.
A typical example of lingering potential are stones caught in a ladder. Any move along the lines of the ladder can break it, hence save the stones and severely affect the overall position.
Leaving the lingering potential allows for some degree of flexibility. There is a strong notion of timing to the concept.
There is no way that White can save her marked stones immediately. The moment a white stone is placed at one of the circled points, however, the potential of those stones comes to life and the lower black stones are threatened with capture.
A forcing move is a move that
Forcing moves mostly remove any lingering potential that might have been available. There is a strong notion of timing to the concept.
After a sequence of forcing moves, the functionality of the opponent's stones has not essentially changed, while the forcing stones keep some future purpose.
In this position, Black has a few forcing moves. He starts off with . If unanswered, White's position would completely crumble.
then forces White to take the two stones. White may decide (but is unlikely) to abandon her three stones, depending on the rest of the top side. Next,
forces once more to effectively take the stones off the board. Next, Black can play along the left side or connect around c.
and
are played to keep the initiative while building the position.
is treated as disposable and will produce its effect later, because it will allow for keeping the initiative with b when white plays a. If Black treated
as essential and defend at a, then he would lose the initiative
Against the hane there are three basic techniques: the cross-cut at a, the counter-hane at b and stretching at
c. These choices are influenced by surrounding stones.
If the contact play is not supported, then it was probably played in Black's sphere of influence, in order to extract something. Cross-cutting creates four groups on the board and it becomes increasingly difficult to capture or save everything. White's intention to get something is well served by the cross-cut. White's play is light and he must have a strategic reason for that.
A counter-hane also leaves the option for Black to cut at a. Black has many options to follow up, one of these being a connection at b. The fact that this connection is possible, makes it a little more difficult for White to ''get
something'': the connection says "all or nothing". So, this move, while being full of flexibility, is a little heavier than
the cross-cut.
The stretch at is mostly seen when the intial contact play is supported. The move creates a simple connection, which
immediately reduces to 3 liberties. The two stones are weak and no part of it can be sacrificed. White's play is heavy. This is why we see it mostly with support and not in Black's sphere of influence. Black
is called Hane at the Head of Two Stones and is considered locally very bad for White.
After , which was so good that it was imperative, Black has two local answers, if there is no support. Leaving it, maybe oddly so, is also an option. It's worth going into this.
If we compare "doing nothing after a hane" and "doing nothing after a stretch" (after an initial contact play), we see that the stone is more easily captured after a hane. Moreover, capturing the stone after a stretch leaves the marked stone without function: the four other stones have captured an enemy and hence connected themselves. So, the marked stone connects connected stones. That's very inefficient: we would prefer to have used it for something else. That's why, the hane creates an urgent position, but the stretch not that much: the White stone is light in the latter case.
Jumping away to is a more advanced techique. The structure is lighter, but due to a good follow-up for Black, also quite urgent.
The knight's press is actually a supported diagonal check. Just like the contact play, the diagonal check is bad in itself, but when supported by other stones it can be locally good. Black's answer a would result in a loss of liberties for Black, so he will reply at b, because, like a it stretches against the diagonal check which is the only local move. The main purpose of is to block the development of the Black stone to that direction. When done from center to side, this is called to press.
After -
, White's connection is strengthened and Black has not increased his liberties. There would only be a purpose in
if followed-up by a cut at a, but then White will further reduce the liberties of the Black stones, while completely enclosing them. In unsupported environment, this is hardly affordable.
So Black answers at here and White increases her liberties as shown before, by answering the stretch with another stretch.
undermines the base of the black stone, creating a base for the friendly stone. Without the context of the bottom line, this move is a matter of mutual development.
The attachment is typically a move in hostile environment. White seeks quick settlement, not necessarily saving all her stones.
Black can prevent the above pressing manoeuver, by playing a diagonal move. Black now aims himself at pressing White down at a. This shows a fundamental relationship between the diagonal and the knight's move.
Black's one space descent? prevents being undermined like in the second diagram. Without the context of the edge it is a matter of mutual development.
A cross-cut in isolation is unlikely to occur: the position is so urgent that the player creating it puts himself at a disadvantage by giving the initiative to the other player. It is more likely for a cross-cut to appear with supporting stones.
However, for clarity of later discussion, the isolated position is worth discussing. There are four groups here (one stone each) and each group has two liberties left. If one of the groups is captured, the capturing player connects all his stones. The remaining stones are all scattered against a strong position and the result is extremely unbalanced.
The question is: do you try to capture one of the enemy stones, or do you defend one of your own.
The most straightforward thing to do is to make one solid extension (simple connection), doubling the liberties. One big advantage for the player with the initiative is the choice: choice of stone and choice of direction. Of the four possible
solid extensions, probably one is better than the others. Strategic or tactical considerations apply
The other choice for Black is to atari at . In this extremely urgent position, where capture takes control of the whole area, White must save her stone under atari, or the whole exchange would have been pointless. After the exchange, Black has three groups with 2 or 3 liberties. It is difficult to take care of all three. The most logical choice is next to connect at a. Doing all of this instead of simply extending is inspired by the surrounding position.
After Black's connection, captures the cutting stone in a ladder. A ladder is a special technique where the cutting stone cannot be saved, because every time the liberties are raised to 2, the opponent reduces them to 1, and the whole sequence leads to the edge, where it is impossible to increase liberties.
Capturing a stone in a ladder always results from a cross-cut situation. Capturing a stone which does not cut, is not urgent.
Here, and
force White to defend her two groups, while Black ends up with 4 groups. Next, defending with a, b or c becomes urgent. But then ...
spans a net around the cutting stone of her two groups. A net is a special technique, where the cutting stone can not be saved. The net move itself does not reduce any liberties, but as soon as the cutting stone sets itself in motion, the next move(s) will reduce its liberties in a fatal way.
When two stones are in an opposing knight's formation, both can play a diagonal attachment. is a contact play or attachment, but it is diagonally linked to the initial stone. Both the contact play and the diagonal are not the strongest possible moves in themselves, but combined they form an awkward move.
As with the contact play in isolation, this is a very urgent position. White's basic answer is , making a simple connection, which is the strongest shape and very appropriate in close combat. The
-
exchange results in conflicting diagonal and straight development, and we know from a previous section that the straight development has the advantage.
So, although Black had the initiative and kept it, he reached an inferior result than the initial situation.
Then why would anyone play the diagonal attachment? Therefore we have to look at the drawbacks of the simple connection: its lack of speed and flexibility. If in danger, it cannot hasten out of the danger zone and it has to be saved as a whole.
In other words, a diagonal attachment makes the enemy heavy and can be seen as a preparatory move for attack.
Any other straight answer by White ( or a), would result in Black making a tiger's mouth. The tiger's mouth is a very effective shape, because
The move is also efficiënt in this context: the number of stones used is 3 to 2.
Again, we start from an opposing knight's position. This time, Black's attachment at is supported by a one space jump. The attachment in isolation is a weak choice, but the one space jump in isolation is a very good move. So, the combination of both is technically feasible. As the contact play induces an urgent position, White is bound to answer. If she does nothing ...
Black will take full control of the area, by reducing the white stone to 2 liberties. Of course, Black has invested 2 stones more and the position is not as efficiënt as a simple wrapping combination of and
. We may start from the assumption though that the knight's opposition indicated that the area is important, so yielding control as White does here, must be induced by strategic considerations.
White's wrapping move (hane) at is the basic answer: it is the basic answer against a contact play in isolation. This choice of hane stays away from the marked stone, while weakening the contact play of
.
After White's wrapping move, an isolated has the choice of counter-hane at two sides, or cross-cut. However, here we must already take another stone into consideration: the marked one. The connectivity, the eyeshape and the efficiency of Black's stones are at stake.
Wrapping around here is risky: it tries to split a one space jump.
immediately is reduced to 2 liberties. Black has a choice between two atari: a and b. This aggressive move of
is also induced by strategic considerations.
Stretching inward, while frustrating the tiger's mouth, with provokes the ideal move of
, combining its own firm connection of three stones with a reduction of White's liberties.
Any other move, such as stretching outward leads to Black getting a tiger's mouth, which is considered advantageous for reasons outlined before.
After White's basic answer at , Black's basic answer is
. When
-
is played in isolation,
is an inferior choice, because next White will wrap around two stones at a. However, due to the presence of
, Black would then create a tiger's mouth at b which is good. Let's see why other options for
are inferior when
is present.
If counter-hane,
plays atari and Black has four stones with five liberties. Assuming White plays
next, she has 6 liberties for her three stones. Indeed she has a cutting point, but let's look at what the stones accomplish, besides connecting to each other.
Both structures develop towards two sides and block each other's development towards those. But there's something wrong with . If it weren't there, Black's group would have the same amount of liberties, the same connectivity and almost the same scope for development. In other words,
is a wasted stone. Black's structure
-
-
is called an empty triangle. It is very inefficient.
If Black applies his basic move in isolation the other way, as here, White can create complexity by playing atari at
, trying to cut apart Black's intial supported contact play. If we assume that
was an important stone, the choice of having it cut off must be inspired by strategic considerations.
A cross-cut always creates complexity. Here, Black has to take his initial stone into account. As in the previous diagram, if we assume that
was an important stone, the choice of having it cut off must be inspired by strategic considerations.
In this diagram the two stones are one space apart, resulting from a one space approach by either player. One player, say Black, can now attach to the opposing stone, by making a knight's move. The knight's move is weaker than the one space jump, so the support for the contact play here is weaker than in the contact play supported by a one space jump.
Again, White's basic answer is guided by her basic answer to the contact play in isolation, the hane.
The basic answer in this situation is to wrap around Black's attachment, while staying away from his support.
Here, turns into Black's formation. Black naturally cuts. There are four groups in a cross-cut and Black has one group having twice as much liberties as the other.
This extension from a cross-cut is a basic structure, which is advantageous for Black, if no other stones are supporting the area.
This position is usually reached from two initial positions. Black has played a knight's move either from a one space check, or from a knight's check. The third possibility, where White has played a checking move of an existing knight's move development, is exceptional, but at least one exception is well known.
The first move to think about is to cut apart Black's knight's move, supported by the existing White stone. After , Black can capture
in a ladder. The prerequisite for cutting through the knight's move is that the ladder doesn't work.
If the ladder doesn't work, both sides can strengthen their weak stones to end up with this pinwheel formation.
Since the first cut depends on a ladder, one may be tempted to cut through the keima this way. After , there is no ladder. However, there is another drawback. In comparison with the "good" way of cutting, where White's stronger group forms a simple connection, here White forms a diagonal connection, meeting a simple connection. As said before, in such meetings, straight is much better than diagonal. Hence, this way of cutting is not preferred. This is not to say that it will never be the solution.
is a supported contact play.
is the basic answer, a hane staying away from the supporting stone.
assures the connection of her three stones, reinforcing the whole position. Next, Black can choose a, to block White's development in this direction, or b or c to connect.
The hane inside White's knight's move is complex. Black must somehow restore the connection of his initial structure while giving some sense to . In many cases this will prove too much to handle, so this technique is reserved for special circumstances.
Another way for White to reinforce by playing contact moves is the attach and extend technique.
Black's basic answer is a stretch, away from the supporting stone. Both try to get ahead in this race building influence to top and bottom respectively.
Black has also the more aggressive option of cutting through the keima. In this severe cross-cut position, White has the advantage of moving first.
Black has basic fluent development towards the top and influences the left. White's best possibility for development is towards the right. First, she can choose to reinforce with a contact sequence, at the expense of reinforcing Black's influence to the left.
Again, the outside hane is easiest for Black. Again, White draws back and Black can play a to connect (more stability) or b to develop.
A special technique is to bump with 3. If Black restores the connection, develops towards the bottom and creates some local eyespace.
The technique is special because Black has room to makes things complex: makes a ponnuki and after
, a can be a troublesome cutting point.
Peeping is bad, locally. Black has uninterrupted and straight development. White has diagonal, interrupted development. is a move only played in White's sphere of influence, making the opponent's structure heavy before attacking.
Whenever a stone's basic development is blocked in two ways, like here, White's basic instinct is to cut Black's stones apart at . The fact that Black doesn't care about being cut in this severe way, means that strategically his stones are likely strong, or that he is strategically prepared to sacrifice one.
This position cannot be reached through normal play by White (without support). Her basic reply to any of the diagonal checks would be to stretch, not to jump. Hence, this must be reached by Black playing his stone against White's jump.
The basic move here is to connect at . White's stones are firmly connected and have 7 liberties, giving a very stable position. Black's stone is worth little. So, why would Black ever play this move?
If somehow White cannot answer the peep, Black will not lose the opportunity to push. White must not hesitate but block and maintain maximum overall connectivity. Black can next choose which way to cut.
If White yields with , the difference with the previous diagram is huge: Black has cut White, but stays firmly connected himself, whereas in the previous diagram he must crosscut.
Black is unlikely to play contact moves here, since they are technically bad, so typically he will develop to the upper side, where there is most space.
White's two stones are two spaces apart. The shape is more easily cut than a one space jump. It emphasizes rapid development over instant stability.
On the side it is called an extension. In particular on the third line, it is impossible to cut the two space extension without support. This makes the two space extension on the third line a very efficient configuration, making a nice balance between development and stability.
When the move is made towards the centre it is labeled a two space jump. Now there is no support from the side for connection.
Here you can see ho Black can cut, which he still will be more likely to do with support than without. White catches a stone in a ladder, while Black grabs the original white stone. This is why a two space jump is often used in hostile spheres of influence to sacrifice a stone.
The large knight's move is even weaker and more easily cut than the two space extension. As it is biased to a certain direction, it is taking development into account more than the two space extension.
The basic technique of cutting a large knight's move in isolation is by attaching to one of the stones. Next there is a cross-cut with support (see later).
This is the bad way of cutting: a and b are now equivalent for connecting with a ladder capture.
On the side the large knight's move very often goes from the third to the fourth line, keeping balance between development and stabiity.
However, it is possible to take away the eyespace of the white group, by playing to
. After
, White can play a double hane at a or stretch at b. Depending on the surrounding stones,
can become a succesful invasion.
This move, when the black stone is on 3-4 is known to invite the taisha joseki. In general, there is one best way to cut the large knight apart.
After Black will choose where to connect and White will likely cut the other side, but her marked stone can be caught in a ladder. In the corner, the sides play an important tactical role, so there White's move is possible. In general this large knight move is aggressive and assumes a certain superiority in this area of the board (such as ladder breakers).
If White hanes at the outside, is a very painful move, splitting White's hazama tobi of
and
in a natural way.
The keima at also cuts and results in a windmill formation. Given the fact that White will usually play the large knight in her favourable environment, creating such turmoil is likely bad for Black.
Now is more of a shoulder hit. As always against the diagonal check, Black can answer a (peaceful) or b (cut).