sinan: The answer is wrong. The marked solution doesn't kill actually. It only captures some stones. However, the move at B15 results in Ko (Gote or Sente depending on the answer). The actual solution should be B15-C15-A12! Now we can kill...
posetcay: Added ko solution, but also kept the previous one. It is hard to argue that one is better than the other, since it depends on the rest of the board, so I kept both.
Added ko solution, but also kept the previous one. It is hard to argue that one is better than the other, since it depends on the rest of the board, so I kept both.