(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[0.00]
PW[White]PB[Black]AW[nc][dd][cn][dp]AB[fc][pd][cf][pf][qk][qo][fq][pq]C[Notes on corner variations and 3-3 invasions]PL[W]
(;W[qc]C[3-3 invasion into one space high 4-4 corner]
(;B[qd]C[Wrong move]
;W[pc]C[Easy points for white])
(;B[pc]
;W[pb]
(;B[ob]TR[ic][jc][kc][id][jd][kd]C[Rule of thumb - Block if black has a stone in the side areas]
;W[qb]
;B[oc]
;W[re]
;B[rf]
;W[qe]
;B[qf]
;W[pe]
;B[oe]
;W[of]C[What if white cuts? DO NOT ATARI]
(;B[nf]C[Black has two weaknesses after atari]
;W[og]LB[ne:A][qh:B]C[Now black has two weaknesses]
(;B[qh]
;W[ne]C[Painful cut])
(;B[ne]
;W[qh]C[Black Captured]))
(;B[ne]
;W[og]
;B[ph]))
(;B[qd]SQ[ic][jc][kc][id][jd][kd]C[Rule of thumb - Block here if white has a stone around the square area]
;W[rb]
;B[rc]
;W[qb]))
(;AE[nc][dd][pf][qk][cn][dp][fq][pq]
;B[pc]
;W[qd]
;B[qe]
;W[re]
;B[qf]
;W[pb]
;B[ob]
;W[qb]
;B[nc]C[What if white tenuki?]
;W[dp]
;B[rf]C[White can still live]
(;W[rd])
(;W[sd]C[White lives but gets reduced a bit]
;B[sf]C[Is this sente for white?]
(;W[dd]
(;B[pa]C[Hane of death?]
;W[sb]C[not this time. White lives.]
;B[ra]
;W[qa]
;B[se]
;W[oa]
;B[na]
;W[rd])
(;B[sb]
;W[sc]
;B[se]
;W[rb]
;B[rd]
;W[sa]C[White lives in the corner. Good end game, I guess.])
(;B[rd]C[Killing move.]
;W[rc]
;B[sb]
(;W[se]
;B[sc]
;W[rd]C[White is dead in the corner])
(;W[pa]
(;B[se]
;W[ra]C[White lives with black mistake])
(;B[ra]
;W[rb]
;B[se]C[White is dead in the corner]
;W[rd]
;B[oa]C[Dead four in the corner.]
;B[sa]
;W[pp]
;B[sc]
;W[qa]
;B[sb]
;W[sa]
;B[ra]C[Looks like ko, but this ko can only be started by black. So under most rules, this shape is deemed to be dead.]))))
(;W[sb]C[Proper move to live]))))
(;B[cq]C[3-3 invasion into knight jump 4-4 corner]
;W[dq]
;B[dr]
(;W[cp]
;B[br]
;W[bq]
;B[cr]
;W[ck]C[Even exchange])
(;W[er]
;B[cr]
;W[eq]
;B[bo]
(;W[co]C[Typically inferior to blocking B6]
;B[bn]
;W[bm]
;B[cp]
;W[cm]C[White looks strong, but black can do a lot of things here. See model variations]
;B[fr]
(;W[es]
;B[fo]C[Black has good shape on the outside])
(;W[fp]
;B[gp]
;W[go]
;B[fo]
;W[ep]
;B[hp]C[White has a dumpling shape and is inefficient]))
(;W[bn]
;B[co]
(;W[do]
(;B[dn]C[What is white cuts? DO NOT ATARI]
(;W[dm]C[White has two weaknesses after atari]
;B[en]
(;W[fp]
;B[cm]C[Painful cut for white])
(;W[cl]
;B[fp]C[Five white stones are in trouble]))
(;W[cl]
;B[en]
;W[fp]
;B[el]C[White can handle both groups]
;W[ao]C[Black is dead in the corner]
(;B[ap]
;W[cp]
;B[bp]
;W[bq])
(;B[bp]C[Empty triangle]
;W[ds]
;B[cs]
;W[ap]
;B[aq]
;W[br]
;B[an]
;W[ao])))
(;B[cp]
;W[dn]C[Proper exchange for both sides]))
(;W[dn]C[What if white does not want to get cut and extend?]
;B[cf]
;W[ao]
;B[ap]LB[do:A]C[Black can block now since it has a liberty]
;W[ar]
;B[cp]
;W[an]
;B[ds]
;W[bp]
;B[bq]
;W[aq]C[This is ko for life for black]))))
(;B[qp]
(;AE[dd][pf][qk][cn][pq]AW[lc][qg][oj][qj][co][fq][hq]AB[nc][qe][ol][ql][cm][jp][nq]PL[B]
(;W[qc]C[White has stones on both sides of the enclosure. Can black capture?

Rule of thumb - white can live if it has help from both sides]
(;B[rd]
;W[ob]
;B[oc]
;W[nb]
;B[pb]
;W[mc]C[White reduced black and left a bad aji in the corner])
(;B[qd]
;W[pb]C[Variation for white to live - incomplete..])
(;B[pc]
(;W[pb]
(;B[ob]
(;W[rb]C[Bad move by white. Cannot live.]
;B[rd]
;W[rc]
;B[qa]C[White dead in the corner.])
(;W[rd]
(;B[re]
;W[rb]
;B[pa]
;W[qa]C[White has ko for life in black's corner. Good ko for white.])
(;B[qb]
;W[rb]
;B[pa]
;W[re]C[Compromise. White reduced black's corner.])))
(;B[rc]
;W[rb]
;B[rd]
;W[nb]C[Marked stone is helping white. Black must block. ]
;B[mb]
;W[ob]
;B[mc]
;W[sb]C[White lives? Not really.]
;B[na]
;W[oa]
;B[qa]SQ[pb]C[White is dead, despite all the help. Q18 is a bad move for direct life.]))
(;W[rd]
(;B[re]
;W[pb]
(;B[rb]C[Kill white]
;W[qb]
;B[ob]
;W[ra]
;B[sb]
(;W[pa]
;B[sd])
(;W[se]
;B[sf]
;W[sd]
;B[rf]
;W[pa]C[White lives... because there are helping stones around.]))
(;B[ob]
;W[rb]C[Ko variation]))
(;B[dd]
;W[cc]LB[ec:A][ce:B]C[Black's enclosure is not perfect, despite three stones. Should have played at A or B.

White invades.

Black can still capture! but leaves some bad aji behind.]
(;B[cd]
;W[dc]
(;B[ec]
;W[bd]
;B[be]
;W[bb]
;B[ad]
;W[ac]C[Ko variation.])
(;B[eb]C[Strong move to kill!]
;W[ec]
;B[ed]
;W[db]
;B[fb]
;W[bb]C[White lives outright without ko.]))
(;B[eb]C[Move to kill.]
(;W[cd]
;B[ce]
;W[dc]
;B[ec]
;W[db]
;B[bd]C[White can't live])
(;W[be]
;B[bf]
;W[ce]
;B[de]
;W[db]
;B[ae]C[White dies in the corner.]
(;W[bd]
;B[bb])
(;W[bb]
;B[ac]C[White is dead here as well.]
;W[ab]
;B[ca])))))))
(;B[cq]C[Black has stones on only one sides of the enclosure. Can White capture?

Rule of thumb - black can't live if white has help on one side]
;W[dq]
(;B[dr]
(;W[er]C[Ko variation - black can do better]
;B[bp]
;W[bo]
;B[br]
;W[ds]
;B[cs])
(;W[bq]
;B[br]
;W[bp]
;B[er]
;W[fp]
;B[fr]
;W[gr]
;B[ar]
;W[fs]
;B[es]
;W[cs]C[Black dead in the corner]))
(;B[bp]
;W[bo]
(;B[br]
;W[dr]C[Prevent the double tiger's mouth]
;B[aq]
;W[cr]
;B[cp]
;W[ao]
;B[ap]
;W[bs]C[Black dead in the corner])
(;B[dr]
;W[br]C[Prevent the double tiger's mouth]
;B[cr]
;W[bq]
;B[cp]
;W[ap]
;B[do]
;W[er]C[Black dead in the corner]))))
(;AE[dd][qk][pq]AW[pf][qf][qj][ck][qn]AB[kc][nc][qe][jp][mp][oq]
(;W[od]C[Tricky play by white]
;B[oc]
;W[qc]
(;B[pc]C[No good by black]
;W[re]
;B[qd]
;W[rd]
;B[rc]C[White reduces black])
(;B[qd]C[Empty triangle]
;W[pc]
;B[oe]SQ[od][cn]C[Ladder does not work for black right now])
(;B[re]C[Sealed off white with weaknesses]
;W[pc]
;B[oe]
;W[pe]LB[nd:A][qd:B]C[Black can choose A or B, but white will take the other])
(;B[pe]C[Empty triangle, but a tesuji]
(;W[pc]
;B[oe]
(;W[rd]
;B[re]
;W[rb]
;B[of]C[black gets out strongly])
(;W[nd]
;B[md]
;W[ne]
;B[of]C[White is divided on all sides]))
(;W[re]C[Proper move by white]
;B[rd]
;W[rf]TR[rc]C[Black must continue]
(;B[dd]
;W[rc]C[White gets in the corner])
(;B[rc]
;W[oe]SQ[pc]C[Black must continue]
(;B[dd]
;W[pc]
;B[qd]
;W[rb]C[White captures black stones])
(;B[pc]C[Good variation])))))
(;W[eq]C[Kicking stone may be sente, but worth very little as it does not defend the corner.]
;B[fp]
;W[en]C[White realizes mistake and comes back to fix. It already has some help from one side.]
;B[cq]
(;W[cp]
;B[er]C[White lets black have some territory. White can do better.])
(;W[er]C[Block to capture.]
;B[bo]
;W[cp]
;B[bp]
(;W[bn]C[This block actually lets black live]
;B[br]C[Black alive])
(;W[cr]
;B[br]
;W[dq]
;B[bn]
;W[cm]
;B[bq]
;W[bs]
;B[bm]
;W[bl]C[Black dead in the corner. 6 stones in a row on the second line dies.])))))
(;B[qo]
;AE[dd][pf][qk][fq]AW[lc][qf][qj][fp][jq]AB[nc][dj][cn]PL[W]
(;B[rd]C[Proper move to defend the corner])
(;B[qe]C[Sente move for now but does not defend the corner]
;W[pf]C[White will come back to 3-3...]
(;W[qc]
(;B[re]
;W[ob]
;B[nb]
;W[oc]
;B[od]
;W[nd]
;B[md]
;W[ne]
;B[mc]
;W[rc]C[Black is captured in it's own corner])
(;B[pc]
;W[re]
(;B[qd]
;W[rd]
;B[rc]
;W[le]C[Black takes one stone... but it is still not fully alive]
;B[dd]
;W[rb]
;B[qb]
;W[sc]C[Black can still be attacked])
(;B[rd]
;W[qd]
(;B[pe]C[Black cannot connect because...]
;W[rc]C[white gain a lot])
(;B[rc]
(;W[qb]C[White cannot extend because...]
;B[pe]LB[rb:B][rf:A]C[White's 3 stones are captured])
(;W[pe]
;B[qb]C[Black is fully alive.])))))
(;B[ne]TR[qe][pf][qf]C[Black needs to further defend with this move to secure the corner, since it kicked the white stones with marked stones.]
;W[qc]
(;B[rd]C[Improper way to defend]
;W[pc]
;B[oc]
;W[rc]
;B[qd]
;W[ob]
;B[nb]
;W[oa]C[White shape has ko in the corner. ]
;B[rb]
;W[sb]
;B[qb]
;W[pb]
;B[qa]
;W[ra]
;B[sa]C[Here is the ko. Good for white.])
(;B[qd]
;W[pc]
;B[oc]
;W[rc]
;B[rd]
;W[ob]
;B[nb]
;W[oa]C[Ko variation for white's group in black's corner. Good for white.])
(;B[re]C[Proper move to kill white]
(;W[pc]
;B[oc]
;W[ob]
;B[nb]
;W[oa]
;B[sb]LB[oa:C][pa:A][pb:B]C[Black kills with monkey jump. Same even if white defends differently. ])
(;W[ob]
;B[nb]
;W[oc]
;B[od]
;W[rb]C[White has good shape... but...]
;B[oa]
(;W[pb]
;B[sc]
;W[sb]
;B[qa]C[White is dead in the corner.])
(;W[rd]
;B[qa]
;W[ra]
;B[sc]C[White is dead in the corner]))))
(;B[dd]
;W[oj]C[White jumps.]
;B[rf]
;W[rg]C[This exchange MAY be beneficial for black.

Only do this when white is already strong.]
;B[lq]
;W[qc]
;B[pc]
(;W[re]
;B[rd]LB[qd:A]C[White cannot push!]
(;W[qd]
;B[pe]
;W[sf]
;B[rc]C[Black keeps the corner.])
(;W[sf]
;B[rc]C[Usual variation for white. White gets sente.]))
(;W[rd]
;B[re]
(;W[pb]
;B[rb]
;W[qb]
;B[ob]
;W[ra]
;B[sb]C[White dies in the corner.])
(;W[rb]C[Can white live with this?]
;B[pb]
;W[sc]
;B[qb]
;W[qd]LB[pe:A]C[Weakness at A]
;B[pe]
;W[ra]C[White lives.

But this made black strong on the outside, and may not be worth the points in the corner. Reduction variation is usual.]))))
(;W[bp]C[Proper move to defend the corner])
(;W[co]C[Sente but does not defend the corner]
;B[dn]
;W[dd]
;B[cq]
(;W[dq]
;B[bo]
;W[cp]
;B[bp]
;W[bq]C[White gives up territory to black in gote])
(;W[bo]C[White blocks, hwo to live?]
;B[eq]
;W[ep]
(;B[dq]C[Bad move..]
;W[fq]
(;B[br]C[Black lives small])
(;B[fr]C[Death for black group]
;W[gr]
;B[er]
;W[ar]
;B[br]
;W[ap]))
(;B[fr]C[Proper move to live]
(;W[dq]
;B[dr]
;W[fq]
;B[er]
;W[gr]
;B[br]C[Black alive in the corner])
(;W[fq]
;B[er]
;W[gr]
;B[br]C[Black alive in the corner])))))
(;B[kd]
;AE[pf][cn][fq]AW[cc][df][cj][dn][jq][mq]AB[db][nc][hd][qg][po]
(;W[qc]LB[qe:A]TR[qg]C[Black's corner is undefended. Marked stone should have been at A]
;B[qd]
;W[pc]
;B[oc]
;W[rd]
;B[re]
;W[rb]C[Can black kill?]
(;B[pb]
;W[qb]
;B[ob]
;W[sc]C[White alive in the corner])
(;B[sd]
;W[sc]C[Ko for life in black's corner. Good for white.]
;B[rc]
;W[cb]
;B[eb]
;W[rd]
;B[se]
;W[ob]
;B[nb]
;W[pb]
;B[rc]
;W[sb]
;B[qa]
;W[ra]
;B[oa]
;W[qb]C[White alive in the corner]))
(;W[gp]
;B[cq]C[White's corner was totally undefended. Black can live outright.]
;W[dq]
(;B[cp]
;W[co]
;B[dr]
;W[er]
;B[br]
;W[ds]
;B[cs]C[Ko variation for black, but black can do better])
(;B[bp]
;W[cr]
;B[br]
;W[cp]
;B[bq]
;W[dr]
;B[bn]
;W[bm]
;B[cn]
;W[cm]
;B[bs]
;W[an]
;B[ao]C[Black is alive in the corner.])))
(;B[ee]C[What if black completely covers white? Can white live?]
;W[cc]
;B[bd]
;W[bc]
;B[cd]
;W[eb]
;B[ec]
;W[dc]
;B[fb]C[Does white has a living shape?]
(;W[db]TR[db][eb][bc][cc][dc]C[Worst possible move. This is a dead shape.]
;B[ea]
;W[da]
;B[ac]
;W[ab]
;B[ba])
(;W[da]C[Also a dead shape]
;B[ac]
;W[ab]
;B[ba]C[White is dead])
(;W[de]C[Exploit black's weakness]
;B[df]
;W[ad]
;B[bg]
;W[da]
;B[ac]C[Black throw in]
(;W[ab]
;B[ba]C[White is still dead!])
(;W[bb]C[Empty triangle. But white has life.]
;B[ae]
;W[ab]C[White is alive in the corner]))))