Xuanxuan Qijing Problem 13: White to play and make a ko
玄玄棋经 · Problem 13 of 347 · Throw-in for a two-stage ko
White cannot live outright here. Look for a sacrifice in the corner that turns the position into a ko.
How to solve it
This problem is known as 'Old Hermit Refining the Pills of Immortality' (仙老煉丹). White's stones along the top cannot make two eyes outright. White pushes in at B17 and, after Black's A17, throws in at A18.
If Black captures the stone at B17 with C17, White plays B19 and the corner becomes a two-stage ko. Sensei's Library gives this as the best result for both sides.
If Black captures the throw-in with A19 instead, White captures at C17 and, after Black's B15, exchanges H17 for H18 and probes at G18. Whichever way Black answers, White gets at least a direct ko, and against some replies lives without one.
Main line
- 1. White B17
- 2. Black A17
- 3. White A18
- 4. Black C17
- 5. White B19
Solution checked against Sensei's Library.
Play it out on the board
Place the stones yourself and see the refutation when you miss. All the Xuanxuan Qijing problems as quick lessons.