(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
AW[cj][dk][dl][cn][en]AB[ec][cd][ch][cl][bp][dp][fq]C[[Written by Jack Jin, jackjin1988@hotmail.com\]

White has just played the marked invasion.

If w c10 group is strong as this case, b cant be aggressive here]
(;W[cf]
(;B[eh]
;W[ef]
;B[gh]
;W[gf]C[if both jump out, good for w])
(;B[dg]C[black can't keep white inside]
(;W[df]C[it is not good for w if w pushes]
;B[ef]
(;W[ee]
;B[de])
(;W[eg]
;B[eh]
;W[fg]
;B[ee]
;W[fh]
;B[bf]C[A tesuji
white can keep black inside and create thickness, but white is a little overconcentrated, not good for white]))
(;W[de]C[this is a good move]
(;B[ef]
(;W[ee]C[white can't push here]
;B[fe]
;W[dc]
;B[dd]
;W[ed]
;B[fd]C[w is short of liberties]
;W[cc]
;B[ce])
(;W[dd]
;B[dc]
;W[cc]
;B[bc]
;W[cb]
;B[bd]
;W[fe]C[w can escape]))
(;B[fd]C[This is often good shape]
;W[fe]C[but white splits black, a tough fight for black]
;B[fg]
(;W[dd]
;B[dc]
;W[cc]
;B[bc]
;W[cb]
;B[bd]
;W[ge]
;B[bf]
;W[bg]
;B[cg]
;W[be]
;B[ce]
;W[af]
;B[df]
;W[ee]
;B[bf]
;W[ep]
;B[eq]
;W[cf]
;B[bb]
;W[bh]
;B[bf])
(;W[ed]LB[bf:A]C[This is a biyt painful, but fixes the connection at A for black]
;B[dd]
;W[ee]
;B[fc]
;W[gf]C[White continues the attack]))))
(;B[df]C[kosumi doesnt work, so the best way for b is sacrificing c12]
;W[dg]
;B[ef]
;W[ce]
;B[dd]
;W[cg]
;B[eg]
;W[dh]C[it is w rights to get some benefit here
it's b sente and b can get another big point])
(;B[ef]SQ[ch]C[another move, the main idea is to sacrifice the marked stone and to get sente]
;W[dg]
;B[eg]
;W[dh]C[Possible]))
(;AW[qj][qm]AB[oc][qd][qh][qo][pp]C[In this case, when white invades on the right side black can be more aggressive.

]
;W[qf]
;B[pi]C[Black can now play this kosumi instead, 

White has two weak groups, black only has one, so it is harder for white than it is for black.]
;W[pj]
(;B[of]
;W[pe]
;B[nd])
(;B[oi]
;W[oj]
;B[nj])))
