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Frosted Board

Puzzle #23: Reversi

  • DifficultyMedium
  • To moveDark
  • TaskOnly winning move
  • Main line8 half-moves

Dark to move. There are 33 dark and 23 light discs on the board and 8 empty squares.

You have 4 legal moves and only one of them keeps the ending won: with perfect play on both sides it finishes 44–20. Each of the 3 alternatives was searched to the last disc and draws or loses.

What the position is about

  • corner — The fight is about a corner square: once taken, it can never be flipped back.
  • only winning move — Every legal move was solved to the end: this one wins, all the others draw or lose.

Finding the way in

With eight empties left, count where the last move in each region will fall; the winning move often gives up discs now to keep the final say.

Take your time. There is no clock on the result, and a wrong move is simply taken back so you can look again.

Show the first move

Start with a1. Played out against the stiffest resistance, the whole line goes: a1 h1 d1 h3 f1 h5 h2 a8.

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.