Computer Games: Eight Pieces Cannot Cover a Chess Board

Abstract

The problem of maximising the number of squares on a chess board which can be attacked by a configuration of the eight main pieces was first posed in 1849. We report on a computer search which proves that at most 63 squares can be simultaneously attacked, and we give results for other variations of the problem. Our search technique, which pruned the space of 2.27 × 10¹² positions to 1.03×10⁸, is of independent interest.