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Frosted Board

Puzzle #31: Reversi

  • DifficultyHard
  • To moveLight
  • TaskOnly winning move
  • Main line11 half-moves

Light to move. There are 23 dark and 30 light discs on the board and 11 empty squares.

You have 5 legal moves and only one of them keeps the ending won: with perfect play on both sides it finishes 37–27. Each of the 4 alternatives was searched to the last disc and draws or loses.

What the position is about

  • edge square — The key move is on the edge of the board, where discs are harder to flip.
  • only winning move — Every legal move was solved to the end: this one wins, all the others draw or lose.

Finding the way in

Eleven empties are too many to guess. Start with the moves that take away the opponent's options or force a pass, and check whether the corner you are tempted by really holds.

Play the position in your head from the opponent's side: what would you do against your favourite move? If there is a good answer, try the next candidate.

Show the first move

Start with h5. Played out against the stiffest resistance, the whole line goes: h5 a1 a5 a8 d2 a3 c1 b1 a2 g1 h2.

Solve it and the next puzzle of the same game is one tap away. Your solved puzzles are ticked in the list, in this browser only.