(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PB[Black to play and kill]AW[mq][nq][oq][pq][mr][qr][rr][sr][ms][ns][os][ps]AB[mp][np][op][pp][lq][qq][rq][sq][lr][or][pr][ls][rs]
;B[qs]C[This is the key move in this shape, even though it looks like
Black is just losing another stone.]
(;W[ss]C[If White takes these two stones...]
;B[qs]C[... then Black plays inside again.]
;W[nr]
;B[pr]C[...and inside again to create the double snap-back shape.
Whichever black stone White takes, White is still in atari.]
(;W[rs]
;B[qs]LB[nr:4][pr:5][qs:7][rs:6][ss:2])
(;W[or]
;B[pr]))
(;W[nr]C[If White captures these two instead, the same shape ensues when Black plays back inside.]
;B[pr]))
