(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
GN[168cx]PB[Black to play: to kill or only capture some?]AW[rp][sp][oq][pq][rq][or][qr][os]AB[qn][ro][op][pp][qp][nq][qq][nr][ns]
(;B[pr]C[This move looks like it can kill.]
(;W[rr]C[But does not if  White connects here]
(;B[ps]
(;W[sr]C[White lives.])
(;W[qs]C[White mistake]
;B[sr]))
(;B[qs]C[Black may play here too, may prefer the previous line
that leaves a ko threat, rather than this immediate point reduction.]
;W[rs]
;B[ps]
;W[sr]C[White can live after giving up four stones.]))
(;W[ps]C[However if white takes.. ]
;B[rr]C[... now the 2-2 point catches White out.]
;W[sr]
;B[rs])
(;W[sr]C[If White tries for corner eyes this way...]
;B[qs]
(;W[rr]
;B[rs]C[... then this dies...])
(;W[rs]
;B[rr]C[... but this way White has to fight ko for everything. ]))
(;W[qs]
;B[sr]
(;W[rr]
;B[ps]C[Again a bent four shape.])
(;W[ps]
;B[rr]))
(;W[rs]C[White should not do this either.]
;B[sr]
;W[ps]
;B[rr]C[Again the 2-2 point causes problems.]))
(;B[rr]C[The 2-2 point often causes a shortage of liberties.]
(;W[rs]C[If White plays this atari then it does.]
;B[sr])
(;W[sr]C[However this atari is okay.]
(;B[rs]
;W[qs]
;B[ps]
;W[ss]
;B[pr]C[Black can capture four stones only.])
(;B[ps]
;W[rs]
;B[pr]C[This is slightly better for black but still does not kill.])))
(;B[ps]C[Sometimes this kind of atrai can create a series of ataris leading to capture.]
(;W[sr]C[Howver it gives White time to make corner eyes.
Black can only capture 4 stones.]
(;B[pr]
;W[qs])
(;B[rs]
;W[qs])
(;B[qs]C[This is black's most severe way of playing.]
;W[rs]
;B[pr]
;W[rr]))
(;W[pr]C[White should not connect here!]
;B[rr]
;W[qs]
;B[rs]))
(;B[sr]C[Sometimes the 2-1 point stops corner eyes.]
;W[rr]C[Connecting here means Black gets nothing/]
(;B[rs]
;W[qs]
;B[ps]
;W[pr]
;B[so]C[White is alive already.])
(;B[qs]
;W[rs]
;B[pr]
;W[ps])
(;B[ps]
;W[pr]))
(;B[rs]C[This 2-1 is similar.]
;W[rr]
(;B[ps]
;W[pr]
;B[sr]
;W[qs])
(;B[qs]
;W[pr]
;B[sr]C[White lives in seki. Capturing the four stones is bigger for Black.]))
(;B[qs]C[This is sometimes a move that catches White's shape lacking by threatening a snap-back.]
;W[rs]C[But not in this position. Black should play one of the lines that captures four stones.]))
