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Frosted Board

Puzzle #18: Reversi

  • DifficultyMedium
  • To moveDark
  • TaskOnly winning move
  • Main line9 half-moves

Dark to move. There are 31 dark and 25 light discs on the board and 8 empty squares.

You have 7 legal moves and only one of them keeps the ending won: with perfect play on both sides it finishes 35–29. Each of the 6 alternatives was searched to the last disc and draws or loses.

What the position is about

  • a pass in the line — Somewhere in the main line one side has no move and must pass.
  • edge square — The key move is on the edge of the board, where discs are harder to flip.
  • draw is the trap — One of the tempting alternatives only draws, so a move that looks good enough is not.
  • 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.

Before you touch a piece, list every forcing move you have and every threat the opponent has; the answer is almost always on that short list.

Show the first move

Start with f1. Played out against the stiffest resistance, the whole line goes: f1 e1 a8 e8 f3 -- g5 h5 h7.

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.