(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]

(;AW[dc][dp]C[[Written by Jack Jin, jackjin1988@hotmail.com\]

]N[YESinvasion-2.sgf]
;B[cf]
;W[cd]
;B[dj]
;W[cl]
;B[ef]
;W[gc]
;B[cn]LB[el:A][dn:B]C[usually white has two choices A or B]
(;W[dn]C[To keep black inside is the first idea]
(;B[co]C[extending here is not good for b]
;W[do]
;B[cp]
;W[cq]
;B[bq]
;W[cm]
(;B[cr]
;W[dq]
;B[bo]
;W[dr]
;B[br]SQ[cf][ef][dj]C[White gets a strong wall at outside in sente, and the marked group becomes quite weak.
This variation is not good for b])
(;B[dq]C[Atari from this side does not work]
;W[cr]
;B[br]
;W[dr]
;B[eq]
;W[er]
;B[fq]
;W[bn]
;B[bo]
;W[ao]
;B[bp]
;W[fr]
;B[gq]
;W[bm]
;B[gr]
;W[bs]C[black is dead]))
(;B[do]C[Black has to wedge, which means that before invading, black has to read the ladder]
(;W[co]C[When the ladder is good for white, white can play this atari]
;B[eo]
;W[cp]
;B[dm]
(;W[bn]C[When the ladder is not good white has to play here]
;B[en]LB[cm:A][fq:B]C[White is busy now, and needs two moves. One at A and one at B]
(;W[cm]
;B[fq]C[Black is happy to get this big point])
(;W[fq]LB[bm:A]C[White has to play here, but the ko aji at A remains]
;B[bm]C[Later, or immediately, if he has enough ko material, black can start the ko]
;W[cm]
;B[bo]))
(;W[en]C[White will extend when the ladder is good for him]))
(;W[eo]C[White has to play here, when the ladder is good for black]
;B[co]
;W[dm]
;B[cp]
;W[dq]
;B[cq]
(;W[cr]
;B[br]
;W[dr]
;B[bm]C[common variation, both ok]
(;W[]
;B[fo]C[if white plays tenuki, this is quite a severe attack]
;W[fp]
;B[en]
;W[ep]
;B[fn])
(;W[fn]C[this is a peaceful way to protect the weakness])
(;W[bl]CR[cf][ef][dj]LB[fo:A]C[This is a more active defence, Black's marked group is under more pressure now.
However A still remains as a weak point for white]
;B[]
;W[bs]C[Later white has a good combination]
;B[ar]
;W[am]
;B[an]
;W[cm]
;B[al]
;W[ak]
;B[ap]
;W[am]
;B[bn]LB[dj:A]C[And we can see that A is very close to white's wall]))
(;W[dr]C[this is another choice, but not that popular]
;B[cr]
;W[fn]))))
(;W[el]C[The simple jump is another choice for white]
(;B[cq]C[if black simply takes the corner, it is not very good]
;W[cp]
;B[dq]
;W[ep]
;B[bp]
;W[bo]
;B[bq]
;W[bn]
;B[fq]
;W[dh]C[white has no weakness, black's group is weak])
(;B[en]
;W[fq]
;B[ck]
;W[bl]
(;B[gn]
;W[gl]C[It is playable for black, but not easy for black to control his two weak groups])
(;B[cp]C[now attaching in the corner is a proper timing move]
;W[cq]
;B[do]
;W[ep]
;B[dl]
;W[dm]
;B[dk]
;W[bp]
(;B[cm]C[This is joseki, both satisfied])
(;B[em]
;W[bn]LB[bo:A]C[Also possible, black aims to play a ko at A later.])))))
(;AW[mc][pc][qd][ql][pp]AB[of][qf][pj]N[YESinvasion-8.sgf]
;B[]C[This is a common shape, black can play tenuki now
Black needs to be prepared for some invasions though!]
(;W[qh]C[One possibility]
(;B[rj]C[overplay]
;W[oh]LB[rh:A]C[black has two weak groups and black can can not get a connection at A
It is hard for black]
;B[rh]
;W[qi]
;B[ri]
;W[qj])
(;B[ph]C[This is honte]
;W[qi]
;B[pi]
;W[qj]
;B[pk]
;W[qg]
(;B[pf]C[A soft move]
;W[pl]C[Black is not happy])
(;B[od]C[A good move]
(;W[oc]
;B[qe]
;W[pl]
;B[ol]
;W[om]
;B[nl]C[Black gets better shape])
(;W[pg]C[This is no problem for black]
;B[og]
;W[pf]
;B[oc]C[it's ok for black]))))
(;W[qi]C[another kind of invasion]
(;B[qj]C[if black wants to seperate white, black will be in trouble]
;W[pg]
;B[pf]
;W[pi]C[black has two weak groups, hard to control])
(;B[pi]C[honte]
;W[qj]
;B[pk]
(;W[pl]
;B[qk]
;W[rk]
;B[rl]
;W[rj]
;B[ol]
;W[om]
;B[nl]C[there's some aji at right side, black is good])
(;W[qk]
;B[om]C[playable for black])))
(;W[ph]C[this is the most popular invasion]
(;B[oh]
;W[pg]
(;B[og]
;W[pf]
;B[pe]
;W[qe]
;B[pi]
;W[rf]LB[oi:A]C[there's still a cutting point at A
white is satisfied])
(;B[pf]
(;W[og]
;B[ng]
(;W[oi]
;B[pi]
;W[nh]
;B[qh]C[very bad for white])
(;W[rg]
;B[oi]
;W[rf]
;B[mf]C[white gets some points, but black gets the influence in center
playable for both]))
(;W[pi]
;B[oi]
;W[qj]
;B[oj]C[another variation, not bad for black])))
(;B[qh]C[another choice for black, not common]
(;W[qi]
;B[pi]
(;W[qg]
;B[pg]
;W[rh]
;B[oh]
;W[qh]C[this is what black hopes for])
(;W[oh]C[A great combination]
(;B[qj]
;W[qg]
;B[ri]
;W[rh]C[in the opening, if black does not have ko threats, it is risky for black])
(;B[ri]C[so this is the correct choice]
;W[qg]
;B[rh]
;W[rg]
;B[pg]
;W[rf]
;B[mf]C[fight, hard for both])))
(;W[pg]C[black is not afraid of this one]
;B[qg]
;W[pf]
;B[pe]
;W[qe]
;B[pi]
;W[oh]
;B[rj]C[it's ok for black])))
(;W[pg]C[black has to be careful for this invasion]
;B[pf]
(;W[qg]C[black does not need to worry about this move]
;B[og]
;W[rf]
;B[re]
(;W[rg]
;B[qe]
;W[oh]
;B[ph]
;W[pi]
;B[oi]
;W[qh]
;B[nh]C[black is good])
(;W[rh]
;B[sf]
;W[rg]
;B[qe]
;W[oh]
;B[ph]
;W[rj]
;B[qi]
(;W[ri]
;B[nh]
;W[oi]
;B[mj]C[white has hurt his corner, so black can give white something on the at right side, it is still good for black])
(;W[oi]
;B[ri]
;W[si]
;B[rk]
;W[pi]
;B[qj]
;W[qh]
;B[oj]C[this fight is good for black])))
(;W[qi]
(;B[qj]
;W[pi]C[Black has been seperated])
(;B[pi]
(;W[qj]
;B[pk]
;W[qk]
;B[ph]C[black is thick, playable for both])
(;W[ph]
;B[oh]
;W[og]
;B[ng]
;W[rg]
;B[nh]
;W[nf]
;B[mf]
;W[ne]
;B[me]
;W[md]
;B[ri]
;W[rh]
;B[qj]
;W[rf]
;B[ke]C[white gets many points, but black gets big influence on the outside, both ok]))
(;B[od]C[black can consider to peep here first]
;W[oc]
;B[pi]
(;W[ph]C[if white still chooses this variation]
;B[oh]
;W[og]
;B[ng]
;W[rg]
;B[nh]
;W[nf]
;B[mf]
;W[ne]
;B[me]
;W[nd]
;B[ri]
;W[rh]
;B[qj]
;W[rf]C[this is better for black than previous one])
(;W[qj]
;B[pk]
;W[qk]
;B[ph]LB[oc:B][od:A]C[so white probably plays this variation instead, the exchange A for B is a bit better for white])))
(;W[qh]C[Not good for white]
(;B[oh]
;W[qj]LB[og:A]C[there's a weakness at A, and it is very comfortable for white to get a connection
so black has to do something actively])
(;B[qi]C[this is the strongest answer]
(;W[ri]
(;B[rj]
;W[pi]
;B[qj]
(;W[oi]
;B[rh]
;W[rg]
;B[si]
;W[qg]
;B[rf]
;W[sg]
;B[oj]
;W[ni]
;B[mf]C[in this variation, b two groups are not easy to be attacked, and much stronger than w weak group
so it is playable for b])
(;W[rg]C[but white can choose this variation]
;B[oi]
;W[ph]
;B[si]
;W[rh]
;B[oh]
;W[og]
;B[ng]
;W[rf]C[there are several cutting points in blacks shape, white is satisfied]))
(;B[ph]C[so this is simple and good choice for black]
;W[oh]
;B[pi]
;W[qg]
;B[og]
;W[rj]
;B[rf]
;W[rh]
;B[nh]C[black is good]))
(;W[pi]C[black does not need to worry about this move]
;B[oi]
;W[ph]
;B[rh]C[double hane is a good move]
;W[ri]
;B[qj]
;W[rg]
;B[sh]
;W[sg]
;B[qg]
;W[si]
;B[rh]C[good for black])))
(;W[pi]
(;B[oi]
;W[qi]C[it is not good for black])
(;B[qi]C[this is the correct choice]
;W[qj]
;B[oi]
;W[ph]
;B[rh]
;W[oj]
;B[pk]
;W[qk]
;B[pl]
;W[pm]
;B[ol]
;W[ni]
;B[qm]C[black is not afraid of this fight])))))
