Dots and boxes problem #524

The task

To move

Dark

Difficulty

Hard

Goal

take 13 of 23 boxes

23 boxes are still unclaimed. The best line gives the side to move a margin of 3. A 5 × 5 board with many chains and perhaps loops. Control is worth more than the boxes on offer.

What to look for

• Decline the last two boxes of a chain to keep control.
• Control: make your opponent open the long chains.

How the answer is checked

There is exactly one first move that forces the result; any other first move allows the defence to escape. Moves that keep the forced result are accepted later in the line, and a move that loses it is taken back with a short note.