(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PW[White]PB[Black]
;B[pd]
(;AW[jc][pd][pn][pp]AB[dd][dp][jp][nq]C[Let's study about the empty triangle!

White 4 is possible. How black respond here?]
;W[]
;B[qf]
;W[qe]
;B[pf]
;W[qj]
;B[od]
(;W[oc]
;B[nd]
(;W[pe]C[We can use empty triangle here. This is the vital point.]
;B[of]
;W[pc]
;B[mg]LB[fc:A]C[Best result for both! After that white can play A .])
(;W[nc]C[If white pushes without empty triangle,]
;B[pc]
;W[qc]
;B[pb]
;W[qb]
;B[pe]
;W[qd]
;B[mc]
;W[ob]
;B[nb]
;W[pa]
;B[ld]C[Black has much better result.]))
(;W[pe]C[This is too early.]
;B[oe]
;W[of]C[Overplay]
;B[pc]
;W[qc]
;B[re]
;W[qd]
;B[pb]C[good move]
;W[qb]
;B[oc]
;W[rd]
;B[rf]C[Game over]))
(;AW[pb][nc][dd][dp]AB[pf][qk][jp][pq]C[In the chinese opening, white invaid lower right corner.
The move 3 is over play. How can you punish this?]
;W[po]
;B[qp]
;W[oq]
(;B[pp]C[The empty triangle is correct.]
;W[op]
;B[oo]
;W[no]
;B[on]C[Black is satisfied.])
(;B[op]C[This is wrong way.]
;W[pp]
;B[qq]
;W[np]
;B[oo]
;W[on]C[The ladder is good for W.])
(;AE[oq]
;B[]
(;W[op]C[Kosumi is a correct move.]
;B[oq]
;W[mp]
;B[nq]
;W[mn]
;B[np]
;W[no]
;B[lo]
;W[mo]
;B[lq]C[This is normal.])
(;W[np]C[In this case black cut another way.]
;B[op]
;W[oo]
;B[no]
;W[qo]
;B[rp]C[Black can fight easily.])))
(;AE[pd]AW[ck][cn][qn][bp][qp][jq][pq]AB[dp][op][cq][gq][lq][oq]
;B[jo]
;W[hp]
;B[gp]
(;W[io]
;B[in]
;W[ho]LB[jn:A]C[This combination is great. After that there is cutting point  A. 
That means. white can escape better.])
(;W[ho]
;B[hq]
;W[ip]C[This empty triangle is too painful. ]
;B[dn]
;W[cm]LB[hm:B][im:A]C[The white group is very heavy.]))
(;AW[dc][jd][pd][de][cl][bo][bp][fp][fq][gq][jq][br]AB[cp][dp][gp][aq][bq][er][fr]LB[aq:B][br:A]C[Upper side:

Black 5 is mistake. White can reduce black's eyeshape.]
(;B[nc]
;W[oc]
;B[nd]
;W[pf]
;B[jb]
;W[jc]
;B[kb]
;W[ib]
;B[ld]
;W[kc]C[The empty triangle is good move.]
(;B[lc]
;W[mb]LB[lb:B][nb:A]C[After that A or B are miai.]
(;B[lb]
;W[nb])
(;B[nb]
;W[lb]))
(;B[lb]
;W[nb]C[This is great for white.]
;B[mb]
;W[ob]C[White's corner is sure and black does not have two eyes. 
White can attack  this continue.])
(;AE[kc][ld]AB[lc]LB[lc:A][nf:B]C[Black A or B are better answer.]))
(;W[eq]C[Difficult to think about this kind of move.]
;B[dq]
;W[cr]LB[cq:B][dr:A]C[A or B are Miai.]
(;B[dr]
;W[cq])
(;B[cq]
;W[dr]))
(;W[dr]C[This looks also good. but..]
;B[cr]
;W[cs]
;B[cq]
;W[eq]
;B[dq]C[There is nothing.])
(;W[cr]
;B[cq]
;W[eq]
;B[dr]C[good answer for B. ]
;W[dq]
;B[gr]))
(;AE[pd]AW[nb][kc][lc][nc][od][oe][jm][co][ho][ko][ep][fp][gp][kp][cq][eq][kq][cr]AB[ic][oc][pc][ld][md][nd][qe][in][io][ip][lp][fq][gq][dr][er][jr]TR[oc][pc][qe][in][io][ip][fq][gq][jr]
(;W[pd]
(;B[qd]C[Wrong answer.]
;W[qc]
;B[qb]
;W[rc]
;B[pb]
;W[rb]C[Black lose the four stones.])
(;B[qc]
;W[qd]
;B[rd]
;W[re]
;B[rc]
;W[qf]
;B[ob]
;W[kd]C[Great for W.]))
(;W[kd]C[If white exchanages this first..]
;B[mf]
;W[pd]
;B[qc]
;W[qd]
;B[rd]
;W[re]
;B[rf]C[The cutting does not work anymore.]
;W[rc]
;B[se]
;W[rb]
;B[of])
(;W[qd]C[Normally we think this move first. ]
;B[pd]
;W[pe]
;B[rd]
;W[qf]
;B[re]
;W[kd]
;B[mf]C[But there is nothing. White two groups are weak.])
(;W[jq]C[This strange move is correct.]
(;B[iq]
;W[hr]LB[hq:A][ir:B]C[A or B are Miai.]
(;B[hq]
;W[ir])
(;B[ir]
;W[hq]))
(;B[ir]
;W[iq]
;B[hq]
;W[hp]C[White is happy enough.]))
(;W[hq]C[This looks also good.]
;B[hp]C[But black can cut easily.]
;W[hr]
;B[gr]
;W[gs]
;B[fr]
;W[jq]
;B[iq]C[nothing.]))
(;AW[pa][nb][ob][pb][pc][qd][rd][qe][rf][qg][rh][co][fo][dp][bq][cq][fq][gq][hq][ar][hr]AB[qa][mb][qb][mc][qc][rc][nd][pe][pf][qf][dq][eq][br][cr][fr][gr]
;W[]
(;B[sd]
;W[re]
(;B[ra]C[This is the only move.]
;W[sb]
;B[nc]C[after that just take the liberties.]
;W[sc]
;B[oc]C[In the end white has shortage of lieberties.])
(;B[sb]C[This move make the semiai ko.]
;W[ra]
;B[nc]
;W[se]
;B[oc]
;W[sc]C[White takes first.]))
(;B[es]C[Black has to use speciality of the corner.]
;W[dr]
(;B[bs]C[This empty triangle is correct.]
;W[ds]
;B[gs]C[Black is alive.])
(;B[ds]C[wrong answer.]
;W[bs]
;B[cs]
;W[gs]))
(;B[ds]C[This wrong direction.]
;W[er]
;B[es]
;W[gs]
;B[fs]
;W[bs]C[Black is dead.])))