(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PW[White]PB[Black to play and save four stones]AW[oo][po][np][qp][jq][lq][nq][qq][jr][nr][pr]AB[mo][no][ip][jp][kp][mp][op][hq][oq][or][os]C[Black can do nothing to the right so has to capture the stones to the left. Black needs to find their weak spot. ]
(;B[mq]C[Pushing through is a good way to reduce liberties on White, especially when followed up by a cut and sacrifice.]
;W[mr]
;B[lr]
(;W[kr]
;B[ls]C[Always sacrifice two stones when reducing liberties.]
;W[ks]
;B[kq]
;W[ms]
;B[lr]
;W[ls]
;B[ir]C[However White has more liberties and Black can not win the race.]
;W[pp]
;B[iq]
;W[pq]
;B[is]
;W[ps])
(;W[ls]C[White can also atari from this side.]
;B[kr]
;W[kq]
;B[ms]
;W[ks]
;B[lr]
;W[kr]
;B[ns]
;W[lr]
;B[ir]
;W[pp]C[White still wins the capturing race.]))
(;B[kq]C[This push is going to end up with a similar result.]
;W[kr]
;B[lr]
;W[mr]
;B[ls]
;W[ks]
;B[mq]
;W[ms]
;B[lr]
;W[ls])
(;B[ir]C[Playing on the outside isn't fast enough..]
(;W[pq]
;B[mq]
;W[mr]
;B[lr]
;W[kr]
;B[ls]
;W[ks]
;B[kq]
;W[ms]
;B[lr]
;W[ls]
;B[is]
;W[pp])
(;W[lr]C[This move is the best defence and White clearly has more liberties.]
;B[mq]
;W[mr]
;B[kq]
;W[kr]))
(;B[lr]C[This is the correct move that aims at White's bad shape.]
(;W[kr]C[This fills a liberty.]
;B[ms]C[This is the correct response which makes good shape.]
;W[mr]C[If white continues here...]
;B[ls]C[... then black calmly connects. ]
;W[ks]
;B[ns]C[White cannot defend both cuts. ])
(;W[mq]C[If White connects here...]
;B[kq]C[... then cuts the five white stones off. ]
;W[kr]C[If White cuts back...]
;B[ms]C[.. then this move again wins the position for Black.]
(;W[ns]
;B[lp])
(;W[mr]
;B[ls]
;W[ks]
;B[ns]))
(;W[mr]C[This move prompts the same move as playing the other side.]
;B[ms]
;W[kr]
;B[ls]
;W[ks]
;B[ns])
(;W[kq]C[This one fails quickly.]
;B[mq]
;W[mr]
;B[ms])
(;W[ls]C[This looks clever, but still gets the same response as filling wither of the other two liberties.]
;B[ms]
(;W[mr]
;B[ks]
;W[kr]
;B[ls]
;W[js]
;B[ns])
(;W[ks]
;B[mq]))))
