(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[7.00]
C[A wall of stones often doesn't make territory near to it funnily enough.

Instead it is used to build a moyo on the other side.]
(;B[pd]
;W[qc]
;B[qd]C[It may look as though B is trying to build the right side but soon we see that B's main follow ups to attack the corner's weakness and l&d come from moves on the upper side (S17 sometimes though it is normally too small). This means it helps B block off the upper side thickly]
;W[pc]
(;B[nc]
;W[oc]
;B[od]
;W[nb]C[This joseki choice by black is often used to get thick in the centre if W threats a moyo in the upper left so B can play O17.

Or if B has potential on the upper side.

]
(;B[mc]
;AW[dc][de])
(;B[rc]
;AB[fc][dd]
;W[rb]
;B[ob]
;W[pb]
;B[mb]
;W[oa]
;B[md]C[I suppose the upper side is pretty much completely sealed off and B at N19 has non-zero impact on the corner's life and death.

Often a wall facing the right doesn't actually build points on the right, but instead makes it impossible for W to invade the top.

The point is that there is so much space on the right that B can't cover it with one move.

In contrast the upper side is mostly sealed off like this]
(;W[pp]
(;B[qn]C[If you play too far away]
;W[pj]C[You opponent reduces naturally and might even make points where you had potential. As W gets closer, the B group may be threatened and hence the upper side might not be B points.])
(;B[qj]
;W[qm]
;B[dp]
;W[pi]C[there are many ways to reduce this area. In any case, B can't really only accept 3rd and 2nd line territory from such a big wall especially as W is reducing the upper side too like this.]))
(;W[qh]C[Normally we find that sooner or later White reduces the wall and depending on the situation, B invades on the right to attack and W has to play very solidly to stay connected (so B makes points on the right and maybe even on the centre and upper side from the attack)]
;B[oh]C[Or it is also ok sometimes for B to build the upper side now.])))
(;B[od]
;W[nc]
;B[nd]
;W[mb]
;B[lc]
;W[dp]
;B[mc]
;W[nb]
;B[pp]
;W[dd]
(;B[fc]C[In this shape, this is often very big move despite being under cut at M18.

The point is that it is awkward for W to reduce this. (W playing M18 is submissive) but invading K17 risks losing the corner with S17 double hane ko (the corner's L&D isn't 100% solid if B gets M18), and B at F17 minimises W's ability to sacrifice the corner with K17.]
;W[ec]C[even this might not be possible]
;B[cc]
;W[fd]
;B[cd]
;W[df]
;B[cf]
;W[cg]
;B[bf])
(;B[cj]
;W[qj]C[when faced with a splitting move, it tends to be very awkward for B to try to attack]
(;B[qh]C[this gets pressed low]
;W[ph]
;B[qg]
;W[qm]C[the efficiency of the wall isn't great]
;B[qo]
;W[pi]
;B[mq]
;W[rd]C[later this is big and B has very few points from the wall])
(;B[ql]
;W[ph]C[The wall isn't alive so this is risky.])
(;B[fc]C[The best strategy is often to extend on top and wait for W's next move to decide how to attack R10.]))))
(;B[qd]
;W[pp]
;B[dp]
;W[dd]
;B[nc]
;W[nq]
;B[fc]C[Curiously, this is often better than approaching in the lower right. (to work with O17).

We used to be taught that you build a shimari like this in order to build the right side, but apparently that's not really true.

O17 is thin, but pushes further into the upper side, but it tends to need some support.

Again, if B tries to build a moyo on the right, when W invades with aji around P16 or P15, it can be difficult for B to handle the attack since the corner isn't solid.

If B wants to add a move on the right, locally B urgently needs to play around Q12 to defend the corner (though R6 is still a much bigger move).]))