Dots and boxes problem #525

The task

To move

Dark

Difficulty

Hard

Goal

take 17 of 25 boxes

25 boxes are still unclaimed. The best line gives the side to move a margin of 9. A 5 × 5 board with many chains and perhaps loops. Control is worth more than the boxes on offer.

What to look for

• A sacrifice: giving material first is the only way to force the result.
• 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.