Chapter 7 · Endgame

Reverse Parity: Leaving a Square the Opponent Cannot Enter

Black's way to take the last move away from White, who holds parity. Leave an odd region White cannot enter (often a single square) and make the rest even; at the end White passes and Black plays that square.

One pass changes who plays the last move. So Black keeps a square White cannot enter empty until the end, and arranges the other regions so that they are all even after each of Black's moves. Then White has to enter even regions first, so Black plays the last move in each region. When everything else is filled, White passes and Black plays the last move on the square left empty.

If Black plays the saved square first, this effect is lost. Also, even a square White cannot enter now is not guaranteed to stay closed until the end. Check that your moves elsewhere do not give White a foothold for that square.

Black to move. Black leaves A2, a 1-square region White cannot enter, and plays A7, reducing the 3-square region to 2 squares so that the rest is all even (2 and 4 squares). After that, Black plays the last move (B8, H8) in each region White enters first, and when White passes, Black plays A2. Black loses by 2 discs, but playing A2 first loses by 14. Use ▶ to play it.

Exercise

Black to move. Of the marked H3 and H7, choose the move that leaves the square White cannot enter and plays elsewhere.

Exercise

Black to move. Of the marked E2 and G7, choose the move that leaves the square White cannot enter and plays elsewhere.

Exercise

Black to move. Of the marked B8 and H2, choose the move that leaves the square White cannot enter and plays elsewhere.

Exercise

Black to move. Of the marked G8 and H3, choose the move that leaves the square White cannot enter and plays elsewhere.

Exercise

Black to move. Of the marked H2 and B8, choose the move that leaves the square White cannot enter and plays elsewhere.

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