(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PW[Chris Oliver]PB[DDK]LB[dd:1][ed:2][fd:3][de:4][ee:5][fe:6][df:7][ef:8]C[Recent relaxations in planning law make it much easier to build an extension
on your house: up to eight metres (six metres where your house is joined to
your neighbours’). Clearly an eight-metre extension won’t work if you have
a three-metre back garden, but likewise, a one-metre extension on a massive
house doesn’t really seem worth the bother. Obvious, right?

This article, aimed at Double Digit Kyu (DDK) players, looks at building the
ideal extensions from walls. What is ideal varies depending on the size of your
wall, the space available to you, and the proximity of your ‘neighbours’ – your
opponent’s stones.

The examples here are principally based on the proverb: ‘from one, two; from
two, three; from three, four’ and the extensions shown are played on the third
line – which is common when looking to develop territory, especially where
it is likely that your opponent will attack. Extensions on the fourth line are
possible, and have their uses 1 but will not feature here.

This type of move would normally take place in the opening phase of the
game, or fuseki, where there is empty space on the edges of the board and
few stones toward the centre of the board.]
(;B[dd]
;AW[jc][mc]AB[cd][qd][ph][qh][ci][di][ei]LB[mc:B][cd:A][qd:C]C[DIAGRAM 1

Note that in this diagram, the extensions stated as ‘two; three;
four’ refer to the number of spaces between the two stones. When
playing from a three-stone wall, count out four spaces, and play on the fifth
intersection, etc.

It is possible to apply this proverb to a wall of four stones (extend five) – and
in some circumstances, even to a wall of five stones – but this will depend on
circumstance, and the larger the extension, the more risk that an invasion by
your opponent will be successful.])
(;B[ed]
;AW[fc][ic]C[The two-space extension – the extension labelled B in Diagram 1 – is a very
common move, and on the third line is used to ‘make a base’. This refers
to creating the architecture for an edge-based group. The formation is very
difficult to cut, as shown in Diagrams 2a and 2b.

When attacked, this formation tends to create
good potential for eye-shape, as you may be able
to appreciate from the Diagram 2a and 2b (right).
However, in order to live, the group must normally
extend, preferably along the side – so choosing to
create this formation when under pressure from
your opponent’s stones can be a mistake. Then,
it can be better to jump toward the centre of the
board . Usually, a one-space jump works well from
the third line.]PL[B]
;B[hc]
;W[hb]
(;B[ib]
;W[gc]
;B[hd]
;W[jb]LB[hb:2][ib:3][jb:6][gc:4][hc:1][hd:5]C[DIAGRAM 2a])
(;B[gb]
;W[gc]
;B[hd]
;W[ib]
;B[fb]
;W[eb]LB[eb:8][fb:7][gb:3][hb:2][ib:6][gc:4][hc:1][hd:5]C[DIAGRAM 2b]))
(;B[fd]
;AB[hc]C[Where Black over-extends, as in Diagram 3, a well-
placed invasion will mean that ‘all your base belongs to
your opponent’. White’s play here is not conventional,
or completely effective, but is fairly typical of DDK-level
play. Black can connect underneath, with a bit of a fight,
but the position as shown is far from secure.]PL[B]
;B[lc]
;W[jc]
;B[jd]
(;W[kc]
;B[kd]
;W[ld]
;B[md]
;W[le]
;B[mc]
;W[id]
;B[ic]
;W[je]LB[ic:11][jc:2][kc:4][lc:1][mc:9][id:10][jd:3][kd:5][ld:6][md:7][je:12][le:8]C[DIAGRAM 3]
;B[jb]
;W[kb]
;B[lb]
;W[ke]
;B[ka]
;W[ib]
;B[ja]
;W[ia]
;B[la])
(;W[id]
;B[ic]
;W[kd]
;B[kc]C[Allowing Black to extend here is suicide; White must capture.]
;W[je]
;B[jb]LB[jb:9][ic:5][jc:2][kc:7][lc:1][id:4][jd:3][kd:6][je:8]C[An alternative strategy from White. This diagram is reproduced with permission from http://senseis.xmp.net/?ExtensionFromAWall under the OpenContent License, which can be found here: http://senseis.xmp.net/?SLCopyright]))
(;B[de]
;AE[de]AB[dc][hc][dd]C[Diagram 4 shows one standard response to
defend against an invasion in the middle of a three-point
extension (extension C in Diagram 1). The obvious choice
for White with no support is to invade in the central
space, rather than making contact with either of the
two black groups. Allowing your opponent a chance to
reduce a single, unsupported stone to only two liberties
is something you should only do when you are certain
about the follow-up.]
;W[fc]
(;B[gd]
;W[fd]
;B[fe]LB[fc:1][fd:3][gd:2][fe:4]C[DIAGRAM 4]
;W[ee]
;B[ed]LB[fc:1][ed:6][fd:3][gd:2][ee:5][fe:4]C[A possible continuation.]
;W[ge]
;B[ff]
;W[gc]
;B[hd]C[Still a significant amount of development to occur in this position. White has made Black strengthen, but the three Black groups cannot connect without capturing some White stones.])
(;B[ee]LB[fc:1][ee:2]C[Apparently this is the normal response for Black here, at a good standard of play. However, I am not sure how the variations play out, and this would be a tough fight for me as Black.]))
(;B[ee]
;AE[ee]AB[eb][cc][ec][jc][ed]
;W[hc]
;B[id]
;W[hd]
;B[he]
;W[fe]
;B[gd])
(;B[fe]
;AE[fe]AB[fc][kc][fd]C[Although it is very commonly observed in DDK games (especially on online
servers such as KGS), playing contact should be a last resort in the fuseki. A
simple (but by no means definitive) guide is as follows: take corners; occupy
space on the edge; strengthen your weak groups by extending from them (or
by making an enclosure in the corner); develop influence; make good shape;
threaten your opponent’s weak groups (especially by capping  or pincering).

The best moves are those which perform more than one of the functions above.
Lower priority would be direct attacks launched from a position of strength,
and lowest would be invasions or attacks from a position of weakness. There
are circumstances where invasions are the best and most urgent move, but
these will be situations where your opponent’s position is overstretched, or
their play has contained errors. Remember: a failed invasion is a double gift
to your opponent, as it often establishes their control of a space, while gifting
them prisoners. Reductions (perhaps using a tesuji, cap or pincer), are generally
less risky than invasions, and can be a more effective strategy.]
;W[ic]
;B[id]
;W[hd]
;B[jd]
;W[he]
;B[hc]
;W[gc]
;B[hb]
;W[gb]LB[gb:9][hb:8][ib:B][gc:7][hc:6][ic:1][gd:A][hd:3][id:2][jd:4][he:5]TR[kc]C[The marked extension is a space too far. After 9, White will play whichever of A and B Black doesn't play - and either way it looks pretty much like Black is cut.]
(;B[gd]
;W[ib]
;B[fb]
;W[ha])
(;B[ib]
;W[gd]LB[gb:9][hb:8][ib:10][gc:7][hc:6][ic:1][gd:11][hd:3][id:2][jd:4][he:5][je:A][ke:B]C[DIAGRAM 5

The sequence in Diagram 5 shows one way that an
overplay by Black can be punished by White. This is an
example of where an invasion could be the best move,
but note that the white group shown has no potential for
eyes, and must escape or connect out to another White
group. Although Black’s groups are not connected, Black
has good shape on the right, and if there is support on the
left, the two stones there should survive.

The invasion is only valuable if it allows White to take a profit, or to reduce
or threaten Black’s stones. A capping move at A or B would be a different
approach, and a reduction on the fourth line at 2 would play out quite
differently – perhaps allowing White to build a horizontal wall and develop
some significant influence toward the centre of the board.]))
(;B[df]
;AE[df]AW[cc][cd][ce][de]AB[dc][hc][dd]C[There are no proverbs dealing with extensions from walls towards the centre,
and furthermore, the received wisdom is that walls are better used for attacking,
rather than developing territory – so an extension is not the only option that
you should consider.

In all of the above sequences, it should be easy to see how neighbouring stones
could complicate the situation for either player. In the example below, White’s
wall allows the extension to be broken.

]
(;W[fc]
(;B[gd]
;W[fd]
;B[fe]
;W[ee]LB[fc:2][hc:1][fd:4][gd:3][ee:6][fe:5])
(;B[ee]
;W[ed]
;B[ec]
;W[fd]
;B[fb]
;W[gb]
;B[gc]
;W[eb]LB[eb:10][fb:7][gb:8][ec:5][fc:2][gc:9][hc:1][ed:4][fd:6][ee:3]TR[de]C[DIAGRAM 6

White’s hane (marked with a triangle) puts Black’s two stones under a huge amount of pressure, and this group
could struggle to survive. The best option may be to strengthen this weak group before trying to extend or to
connect out of trouble.]))
(;W[cf]
;AE[hc][cf]
;B[db]
;W[cb]
;B[hc]C[This might be a better exchange for Black. Note that Black first strengthens his weak group, and then extends one space less than the proverb would suggest.]
;W[fc]
;B[ee]C[This looks OK for Black - but there is still a lot of aji here.]))
(;B[ef]
;AE[ef]AW[pa][kb][ob][qb][dc][lc][mc][nc][pc][qc][nd][me][qj][mo][dp][np][lq][mq][nq][pq][qq][kr][or][qr][ps]AB[mb][nb][oc][kd][ld][md][od][pd][qd][ne][nf][pj][nn][no][kp][lp][mp][op][pp][qp][oq][mr][nr]LB[qj:1]TR[lj]C[DIAGRAM 7

After all of the sequences above, you may also be able to see that there is
potential left behind for the extension to be attacked further. This potential
is referred to as aji. If you are relying on the strength of a group with lots of
aji late in the game, your opponent may devise moves which both require a
response to preserve this group and which also create potential elsewhere.
Exploiting aji is a highly valuable skill in the mid- to endgame.

Diagram 7 is from a game 4 in the 5 th round of the World Mind
Sports Games, Beijing 2008. It shows a situation where a fourth line ‘extension’
is invaded by White. Black has played in such a way that he stands or falls on
whether this territory remains intact.

In point of fact, the ‘extension’ in this game wasn’t played as such – Black
started out by taking the three star points on the right hand side of the
board, and went on to build walls on either side of the central stone.
The ideal extension to play in between the two walls shown would be the
central point on the third line (at 1), rather than on the fourth. If the
positions of the two stones had been reversed, and White’s invasion had
been on the fourth line, it would have been a much more difficult
proposition for him to live. 

White’s decision to invade, rather than to reduce with a move such as the
marked triangle point was bold; White could easily have failed to live. A fight
like this could have gone either way, even at such a high level of play but in this
case, White went on to win the game.

My thanks to Francis Roads, Ian Davies (Javaness), Dieter Verhofstadt and
Nicholas Jhirad (shapenaji) for their assistance in preparing this article and the
related diagrams.]))
