(;SZ[19]AW[db]AW[bc]AW[cc]AW[dc]AB[eb]AB[gb]AB[ec]AB[bd]AB[cd]AB[dd]AB[ee]AB[ge]AB[bf]LB[jd:T]C[White is dead, but wants you to prove it. Please move at 'T' for tenuki to start this problem.]GM[1]FF[4]CA[UTF-8]AP[Jago:Version 4.43]ST[2]GN[Clipboard Content];B[jd] (;W[ca] (;B[ac];W[ab];B[bb];W[ba];B[aa]C[Deny the chance of White ko]) (;B[bb] (;W[ba] (;B[ab]C[ CHOICERIGHT]) (;B[ac];W[ab]C[Don't let W try to get a ko];B[aa]C[Deny the chance of White ko])) (;W[ab] (;B[ba]C[ No room for another White eyeCHOICERIGHT]) (;B[aa];W[ba]) (;B[ac];W[ba]C[Stop White from trying the ko in the corner];B[aa]C[Deny the chance of White ko]))) (;B[ab];W[ac] (;B[bb]C[ There is no place for W to get another eye.CHOICERIGHT]) (;B[ba];W[bb]) (;B[aa];W[bb])) (;B[ba];W[bb] (;B[ac];W[ab]) (;B[ab];W[ac]) (;B[aa];W[ab]) (;B[ea];W[da] (;B[ac];W[ab]) (;B[ab];W[ac]) (;B[aa];W[ab]))) (;B[aa] (;W[bb]C[CHOICE] (;B[ac];W[ab]) (;B[ab];W[ac]) (;B[ba];W[ab])) (;W[ab]C[CHOICE] (;B[bb];W[ba]) (;B[ba];W[bb]) (;B[ac];W[ad] (;B[ba];W[bb]) (;B[bb];W[ba]) (;B[ae];W[ba]C[Actually, White does not even need to play this move yet.])))) (;B[cb];W[bb]C[Self-atari does not help here.])) (;W[bb] (;B[da];W[ca]) (;B[cb];W[ca]C[Hello?]) (;B[ca];W[da] (;B[ac] (;W[ba] (;B[ab]C[ CHOICERIGHT]) (;B[aa];W[ab])) (;W[ab] (;B[ba]C[ CHOICERIGHT]) (;B[aa];W[ba]))) (;B[ab];W[ac] (;B[ba];W[cb]) (;B[aa];W[ba])) (;B[aa];W[ba]) (;B[ba];W[ac] (;B[aa]C[White is usually dead here; however, this is less than best, because Black must kill via 'bent-four-in-the-corner'. If White ends up with a non-removable ko threat, then this may end up alive in seki, under some rulesets. Find the more immediate path to victory.]) (;B[ab];W[cb]) (;B[cb];W[aa]))) (;B[ba];W[ca] (;B[ac];W[ab]) (;B[ab];W[ac]) (;B[aa];W[ab]) (;B[ea];W[da] (;B[ac];W[ab]) (;B[ab];W[ac]) (;B[aa];W[ab]))) (;B[aa];W[ba]) (;B[ab];W[ac] (;B[da];W[ca]) (;B[ca];W[da] (;B[cb];W[ba]) (;B[ba];W[cb]) (;B[aa];W[ba]) (;B[ea];W[ba]) (;B[ad];W[aa])) (;B[ba];W[ca]) (;B[aa];W[da]) (;B[ea];W[da])) (;B[ac];W[ab] (;B[da];W[ca]) (;B[ba];W[ca]) (;B[cb];W[ca]) (;B[aa];W[da]) (;B[ca];W[da] (;B[aa];W[ba]) (;B[ba]C[ CHOICERIGHT]) (;B[cb];W[ba]) (;B[ea];W[ba])))) (;W[ba] (;B[da];W[ab] (;B[ca];W[cb]C[White lives -- an eye at 'A' and an eye at 'B'. White just needs to connect at 'C' when Black plays 'D' or (to start ko) 'E'. Try again, Black...]LB[aa:a]LB[bb:b]LB[ac:c]LB[ad:d]LB[ae:e]) (;B[cb];W[ca]) (;B[ac];W[ca])) (;B[ab];W[ac] (;B[aa];W[da]) (;B[ca];W[da]) (;B[da] (;W[ca] (;B[bb]C[ White eyespace is ruinedCHOICERIGHT]) (;B[ea];W[bb]) (;B[aa];W[bb])) (;W[bb] (;B[ca]C[ White has only one eye.CHOICERIGHT]) (;B[ea];W[ca]) (;B[cb];W[ca]))) (;B[bb] (;W[da];B[cb]C[ CHOICERIGHT]) (;W[cb];B[da]C[ CHOICERIGHT])) (;B[cb];W[bb])) (;B[cb];W[bb]) (;B[ca];W[da] (;B[ab];W[ac]) (;B[bb];W[cb]) (;B[aa];W[bb])) (;B[bb];W[ab])) (;W[ab] (;B[aa];W[ba]) (;B[bb];W[ba]) (;B[cb];W[ca]) (;B[ca];W[ba] (;B[da];W[cb]LB[aa:A]LB[bb:B]C[White lives with eyes at A and B.]) (;B[bb];W[cb]) (;B[cb];W[da])) (;B[ac];W[ba]) (;B[ba] (;W[ca];B[bb]C[ CHOICERIGHT]) (;W[bb] (;B[ca]C[ CHOICERIGHT]) (;B[da];W[ca]C[Stop W from getting a ko -- there are better ways to kill.]) (;B[aa];W[ca])))) (;W[ac] (;B[da];W[ca] (;B[bb]C[ Bulky five diesCHOICERIGHT]) (;B[ea];W[bb]) (;B[ba];W[bb]C[ Stop White from trying for ko. Kill more surely.CHOICE]) (;B[ab];W[bb]) (;B[aa] (;W[bb]C[CHOICE]) (;W[ba] (;B[ab];W[bb]C[CHOICE]) (;B[bb];W[ab]C[CHOICE]) (;B[cb];W[ab]))) (;B[cb];W[bb])) (;B[ba];W[bb] (;B[da];W[ca]C[Deny White a chance at ko.]) (;B[ca];W[da] (;B[ab];W[cb]) (;B[aa]C[This kills via 'bent-four in the corner'. If White develops an unremovable ko threat, then Black may find that White lives in seki, under some rulesets. There is a better way to kill this.])) (;B[aa];W[ca]) (;B[ab];W[ca]) (;B[cb];W[ca]) (;B[ad];W[ca]) (;B[ea];W[ca])) (;B[ca];W[da] (;B[bb];W[ba] (;B[aa] (;W[cb] (;B[ea];W[ba]C[Don't let W try for a ko.]) (;B[ab];W[ba]) (;B[ad];W[ba]C[Don't let White try for ko]) (;B[ba];W[ab];B[ba]C[ This works, but I think it's inferior because... what if White does not play A18 right now, but saves it for a ko threat? Black can kill without giving White such a chance.CHOICERIGHT])) (;W[ab] (;B[cb];W[ba]) (;B[ea];W[ba]C[Don't let White get a ko]) (;B[ad];W[ba]C[Don't let W try a ko]) (;B[ba];W[cb];B[ba]C[ This works, but I dislike it. Suppose W does not capture with C18 right away, but saves it for a threat in a ko fight. Black has better ways to kill.CHOICERIGHT]))) (;B[cb];W[ab]) (;B[ab];W[cb]) (;B[ea];W[cb]) (;B[ad];W[cb])) (;B[ba];W[bb] (;B[ab];W[aa]C[Stop W from trying a ko]) (;B[cb];W[aa]) (;B[aa]C[This sets up 'Bent-four in the corner', which is almost always dead. However, if W comes up with an unremovable ko threat, then White may live in seki, under some rulesets. Find a more direct way.])) (;B[cb];W[bb]) (;B[aa];W[ba] (;B[cb];W[bb]) (;B[ab];W[cb]) (;B[bb];W[cb] (;B[ab];W[ba]) (;B[ba];W[ab];B[ba]C[ This seems to work, but I dislike giving White a ko threat (suppose W does not capture with A18 right now; then Wh. at A18 will be good in a ko fight). There is a simpler way.CHOICERIGHT]))) (;B[ab] (;W[bb]C[CHOICE] (;B[cb];W[ba]) (;B[ba];W[cb]) (;B[aa];W[ba]) (;B[ea];W[ba]) (;B[ad];W[aa])) (;W[ba]C[CHOICE]))) (;B[aa];W[ba] (;B[ab];W[bb]) (;B[bb];W[ab]) (;B[cb] (;W[ca]C[CHOICE]) (;W[bb]C[CHOICE])) (;B[ca];W[ab] (;B[da];W[cb]) (;B[cb];W[da]) (;B[bb];W[cb])) (;B[da];W[ab])) (;B[cb] (;W[bb]C[CHOICE] (;B[ca];W[da]) (;B[ba];W[ca]) (;B[da];W[ca])) (;W[ba] (;B[ca];W[da]) (;B[bb];W[ab]) (;B[da];W[ca]))) (;B[bb];W[ba] (;B[aa];W[ab]) (;B[ca];W[ab]C[Don't let White try for a ko. There is a better way to kill.]) (;B[cb];W[ab]) (;B[ab] (;W[da] (;B[ca];W[cb]) (;B[cb]C[ CHOICERIGHT])) (;W[cb];B[da]C[ CHOICERIGHT])) (;B[da];W[ab])) (;B[ab];W[bb] (;B[ba];W[ca]) (;B[aa];W[da]) (;B[ca];W[da] (;B[aa];W[ba]) (;B[ba];W[cb])))))