Problem	16387
Created	2012-08-15
Source
Rating

Difficulty	11.8 kyu
Average Solve Time	63 secs
User Attempts	489 / 1347
Solve Ratio Rating	6 kyu
	rating history

Black has several ways to defend; in each case there is more than one way to kill.

(;AB[ac]AB[bc]AB[cc]AW[bd]AW[cd]AW[dc]AB[dd]AB[ed]AB[fc]AW[de]AB[gd]AB[ad]AW[ae]AW[bf]AW[cf]C[Best result for the corner is...?]AP[goproblems] (;W[db] (;B[ca]C[Defense nr. 1 (of 3). There are 4 moves that kill now, but only one is straightforward.CHOICE] (;W[cb];B[bb] (;W[aa]C[Black dies, so White lives.RIGHT]) (;W[da];B[aa]C[Approach move ko. Black might as well not play A19 now but tenuki instead and come back to play A19 somewhere in the endgame. So you need to play another move to prevent that.]) (;W[ba];B[aa];W[da];B[eb];W[ba]C[Just ko.]) (;W[ab];B[aa];W[da];B[eb];W[ba]C[Just ko.]) (;W[fb];B[eb]) (;W[eb];B[aa] (;W[gb];B[fb] (;W[fa];B[ea] (;W[da];B[ec]C[Ko]) (;W[ga];B[ec])) (;W[da];B[ec]C[Ko]) (;W[ea];B[fa])) (;W[fb];B[gb] (;W[da];B[fa]C[Ko]) (;W[fa];B[da];W[ea];B[ga];W[ba];B[ca])) (;W[da];B[fb]C[Ko]))) (;W[da];B[bb] (;W[cb];B[aa]C[Approach move ko. Black might as well not play A19 now but tenuki instead and come back to play A19 somewhere in the endgame. So you need to play another move to prevent that.]) (;W[aa]C[White now wins the semeai without ko.RIGHT]) (;W[ba];B[aa];W[cb];B[eb];W[ba]C[Just ko.])) (;W[bb]C[Easy does it.RIGHT]) (;W[ba];B[bb] (;W[aa]C[White wins the semeai without ko.RIGHT]) (;W[cb];B[aa];W[da];B[eb];W[ba]C[Just ko.]) (;W[da];B[aa];W[cb])) (;W[ab];B[bb] (;W[aa];B[eb] (;W[cb]C[];B[ba]) (;W[da];B[ea])) (;W[cb];B[aa]) (;W[da];B[aa];W[cb]) (;W[ba];B[aa];W[cb];B[eb];W[da];B[ea]C[Ko])) (;W[aa];B[cb]) (;W[eb];B[cb]) (;W[ea];B[bb] (;W[aa];B[eb] (;W[cb];B[ec]) (;W[da];B[fa];W[ba];B[ec]) (;W[fb];B[ec]) (;W[ba];B[ec];W[da];B[fa]) (;W[fa];B[da])) (;W[da] (;B[fa] (;W[fb];B[cb] (;W[ga];B[aa]) (;W[aa];B[eb] (;W[ga];B[ec]) (;W[ec];B[eb])) (;W[gb];B[aa])) (;W[cb] (;B[ec];W[ba]) (;B[aa];W[fb] (;B[ec];W[ga];B[eb];W[fa];B[ha]) (;B[eb]))) (;W[aa];B[eb];W[ba];B[ec])) (;B[aa];W[cb]C[Ko])) (;W[cb];B[eb]) (;W[eb];B[aa];W[cb];B[fb]C[Ko]))) (;B[ba]C[Defense nr. 2 (of 3). Two ways to kill this.CHOICE] (;W[bb];B[cb] (;W[ab];B[aa];W[da];B[eb] (;W[ca];B[ea]) (;W[bb];B[ea]) (;W[ea];B[fa]) (;W[ab];B[ea])) (;W[da];B[ab])) (;W[cb]C[];B[bb] (;W[ca]C[RIGHT]) (;W[aa]C[RIGHT]) (;W[ab]C[RIGHT]) (;W[ea];B[eb] (;W[fa];B[da]) (;W[da];B[fa]) (;W[ca];B[ec]) (;W[fb];B[ec])) (;W[eb];B[fb] (;W[ca]C[RIGHT]) (;W[ab]C[RIGHT]) (;W[aa]C[RIGHT]) (;W[ea];B[fa]) (;W[fa];B[ea] (;W[da];B[gb]) (;W[ga];B[ca];W[da];B[ec];W[ea];B[ha]) (;W[ca];B[ec]) (;W[aa];B[ec] (;W[da];B[gb]) (;W[ga];B[ha])) (;W[ab];B[ec] (;W[da];B[gb]) (;W[ga];B[ha])))) (;W[da];B[eb] (;W[ca];B[ea]) (;W[aa];B[ea]) (;W[ab];B[ea]) (;W[ea];B[fa])) (;W[fb];B[eb] (;W[ea];B[ec]) (;W[ec];B[da];W[ea];B[ca];W[eb];B[gb]) (;W[ca];B[ec]) (;W[da];B[ea]) (;W[fa];B[da];W[ea];B[gb] (;W[ec];B[ca]) (;W[ca];B[ec]))) (;W[fa];B[eb];W[ea];B[da])) (;W[ca];B[cb] (;W[ab];B[da] (;W[ea];B[eb]C[Ko]) (;W[eb];B[ea] (;W[fb];B[gb];W[fa];B[ga];W[ca];B[da]) (;W[fa];B[ga] (;W[ca];B[da] (;W[gb];B[fb];W[ha];B[ec]) (;W[ea];B[fb]C[Ko]) (;W[fb];B[gb])) (;W[fb];B[gb];W[ca];B[da])))) (;W[da];B[ab])) (;W[ab];B[cb] (;W[da]C[A semeai, avoiding ko.RIGHT]) (;W[bb];B[aa];W[da];B[eb] (;W[ca];B[ea]) (;W[bb];B[ea]) (;W[ea];B[fa]) (;W[ab];B[ea])) (;W[eb];B[fb] (;W[ca];B[da];W[ea];B[fa]C[Ko]) (;W[da];B[ec]) (;W[ea];B[ca]) (;W[bb];B[aa] (;W[ca];B[ea] (;W[bb];B[da]) (;W[ab];B[da]) (;W[da];B[ec])) (;W[da];B[ec]) (;W[ea];B[ca]) (;W[fa];B[ga]) (;W[bb];B[ec]) (;W[ab];B[ec])) (;W[aa];B[ec]) (;W[fa];B[ga])) (;W[ca];B[da] (;W[ea];B[eb]C[Ko]) (;W[eb];B[ea] (;W[fb];B[gb];W[fa];B[ga];W[ca];B[da]) (;W[fa];B[ga] (;W[ca];B[da] (;W[gb];B[fb];W[ha];B[ec]) (;W[ea];B[fb]C[Ko]) (;W[fb];B[gb])) (;W[fb];B[gb])))) (;W[ea];B[eb] (;W[ca];B[da]C[Ko]) (;W[da];B[fa]) (;W[fa];B[da]C[Ko]) (;W[bb];B[aa] (;W[ab];B[ec]) (;W[ca];B[ec]) (;W[bb];B[ec]) (;W[da];B[fa]) (;W[fb];B[ec]))) (;W[fb];B[eb])) (;W[da]C[];B[eb] (;W[cb];B[bb] (;W[ca];B[ea]) (;W[aa];B[ea]) (;W[ab];B[ea]) (;W[ea])) (;W[bb];B[cb] (;W[ab];B[aa] (;W[ca];B[ea]) (;W[bb];B[ea]) (;W[ea];B[fa]) (;W[ab];B[ea])) (;W[ca];B[ab])) (;W[ca];B[bb] (;W[ea];B[fa]) (;W[cb];B[ea]) (;W[aa];B[ea]) (;W[ab];B[ea])) (;W[ab];B[bb] (;W[ea];B[fa]) (;W[ca];B[ea]) (;W[cb];B[ea]) (;W[ec];B[fb]) (;W[fb];B[ec])) (;W[ea];B[fa]) (;W[ec];B[fb]) (;W[fb];B[ec])) (;W[eb];B[cb] (;W[ab];B[fb] (;W[ca];B[da];W[ea];B[fa]C[Ko]) (;W[da];B[ec]) (;W[ea];B[ca]) (;W[bb];B[aa] (;W[ca];B[ea] (;W[bb];B[da]) (;W[ab];B[da]) (;W[da];B[ec])) (;W[da];B[ec]) (;W[ea];B[ca]) (;W[fa];B[ga]) (;W[bb];B[ec]) (;W[ab];B[ec])) (;W[aa];B[ec]) (;W[fa];B[ga])) (;W[fb];B[gb] (;W[ab];B[ec] (;W[da];B[fa]) (;W[ea];B[ca]) (;W[ca];B[da]) (;W[bb];B[aa]) (;W[fa];B[da])) (;W[da];B[fa] (;W[ab];B[ec]) (;W[ca];B[ec])) (;W[ea];B[ab])) (;W[da];B[fb];W[ab];B[ec])) (;W[fb];B[cb] (;W[ab];B[eb]) (;W[eb];B[gb] (;W[ab];B[ec] (;W[da];B[fa]) (;W[ea];B[ca]) (;W[ca];B[da]) (;W[bb];B[aa]) (;W[fa];B[da])) (;W[da];B[fa] (;W[ab];B[ec]) (;W[ca];B[ec])) (;W[ea];B[ab])) (;W[da];B[eb] (;W[ea];B[gb] (;W[ec];B[ab]) (;W[ab];B[ec]) (;W[fa];B[ga])) (;W[ec];B[gb] (;W[ea];B[ab]) (;W[fa];B[ga];W[ea];B[ab]) (;W[ab];B[fa])) (;W[ab];B[ea])) (;W[ec];B[da];W[eb];B[gb]))) (;B[cb]C[Defense nr. 3 (of 3) featuring 3 ways to kill.] (;W[bb];B[ba] (;W[ab];B[aa];W[da];B[eb] (;W[ca];B[ea]) (;W[bb];B[ea]) (;W[ea];B[fa]) (;W[ab];B[ea])) (;W[da];B[ab])) (;W[ca];B[ba] (;W[ab];B[da] (;W[ea];B[eb]C[Ko]) (;W[eb];B[ea] (;W[fb];B[gb];W[fa];B[ga];W[ca];B[da]) (;W[fa];B[ga] (;W[ca];B[da] (;W[gb];B[fb];W[ha];B[ec]) (;W[ea];B[fb]C[Ko]) (;W[fb];B[gb])) (;W[fb];B[gb])))) (;W[da];B[ab])) (;W[da] (;B[eb]C[CHOICE] (;W[ca];B[ab];W[ba];B[ea] (;W[bb]C[RIGHT]) (;W[aa]C[RIGHT])) (;W[ba]C[RIGHT]) (;W[ab]C[RIGHT]) (;W[bb];B[ba] (;W[ab];B[aa]) (;W[ca];B[ab])) (;W[aa];B[ca]) (;W[ea];B[fa])) (;B[ab]C[CHOICE];W[ba]C[RIGHT])) (;W[ba]C[RIGHT]) (;W[ab];B[da] (;W[ea];B[ba];W[ca]C[Ko]) (;W[ba];B[eb]) (;W[ca];B[ba] (;W[ea];B[eb]C[Ko]) (;W[eb];B[ea] (;W[fb];B[gb];W[fa];B[ga];W[ca];B[da]) (;W[fa];B[ga] (;W[ca];B[da] (;W[gb];B[fb];W[ha];B[ec]) (;W[ea];B[fb]C[Ko]) (;W[fb];B[gb])) (;W[fb];B[gb])))) (;W[bb]C[RIGHT]) (;W[aa];B[eb]) (;W[eb];B[ba];W[ea];B[fb];W[ca]C[Ko])) (;W[fb];B[eb] (;W[ea];B[ec];W[da];B[gb]) (;W[da];B[ea]) (;W[fa];B[da]) (;W[ec];B[da])) (;W[eb];B[ba] (;W[ab]) (;W[fb];B[gb] (;W[ab];B[ec] (;W[da];B[fa]) (;W[ea];B[ca]) (;W[ca];B[da]) (;W[bb];B[aa]) (;W[fa];B[da])) (;W[da];B[fa] (;W[ab];B[ec]) (;W[ca];B[ec])) (;W[ea];B[ab])) (;W[da];B[fb];W[ab])))) (;W[cb];B[db]) (;W[eb];B[db]) (;W[da];B[db]) (;W[ff];B[db]C[Nice wall facing down. Pity you lost the corner though.]) (;W[gf];B[db]C[Black may try to separate G14 from the rest of your stones later. But rescueing the corner is bigger.]) (;W[ba];B[db]) (;W[ec];B[eb]) (;W[bb];B[db]) (;W[ca];B[db]) (;W[fe];B[db]) (;W[ee];B[db]) (;W[ef];B[db]))