(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PB[Black to play]AW[rm][po][qo][pp][qq][qr]AB[pl][rl][pm][pn][oo][op][qp][mq][pq][nr][pr]C[This is the problem position. Black to play]
(;B[ro]C[This is the key move]
(;W[rp]
;B[qn]C[If white takes - black ataris and white cannot live]
;W[qp]
;B[rn]
;W[sq]
;B[rr]
;W[rs]
;B[sr]C[The corner is a well known dead shape.])
(;W[qn]C[If white extends instead]
;B[rp]C[Black just connects and either captures at
bottom or the top.]
(;W[rn]
;B[rq]
;W[rr]
;B[sr])
(;W[rq]
;B[qm]
;W[rn]
;B[sn])))
(;B[rr]C[The clamp is sometimes a tesuji.]
;W[rq]
;B[qn]
;W[ro]
;B[qs]
;W[sq]C[But after this white has two ways of living.]
(;B[rs]
;W[rn])
(;B[rn]
;W[rs]
;B[ss]))
(;B[rn]
;W[ro]C[If black plays this side then white just lives 
after this.]))
