Explanation
Open the explanation (shows the answer)
The answer is d7. With best play to the end: +4 (a win by 4).
Best line: d7 b7 a1 a6 b1 a2 a8 b6 a7 b8
Other moves
| Move | Result | Why |
|---|---|---|
| a1 | -4 (a loss by 4) | The opponent's best answer is d7 (then b6 a6 b1). |
| b7 | -12 (a loss by 12) | b7 is an X-square (diagonal to the corner a8). While the corner is empty it tends to give the corner away. After this move the opponent can play the corner a8. b7 is in an even region (6 empties); d7 is in an odd one (1). The opponent's best answer is d7 (then b6 a2 a1). |
| b1 | -16 (a loss by 16) | b1 is a C-square (next to the corner a1). In this shape it lets the corner be taken. The opponent's best answer is d7 (then b7 a1 a2). |
| b8 | -20 (a loss by 20) | b8 is a C-square (next to the corner a8). In this shape it lets the corner be taken. b8 is in an even region (6 empties); d7 is in an odd one (1). The opponent's best answer is d7 (then a1 a8 b7). |
| b6 | -24 (a loss by 24) | b6 is in an even region (6 empties); d7 is in an odd one (1). The opponent's best answer is a2 (then a1 b1 b8). |
About these puzzles
Each position comes from a real game. The engine solved it to the end (perfect play by both sides) and only positions with a single best move, clearly better than the second-best move, were kept. "Best play wins by N" is the final disc margin when both sides play perfectly.
If you play a different move, you see the final margin your move leads to with perfect play afterwards, and how much it gave up. Results are stored only in this browser.
To be graded during a full game, go to the Reversi dojo.