This game was invented by Haar Hoolim and first published in Sid
Sackson's great collection "A Gamut of Games". The enemy pieces (◎)
try to get the 3 musketeers (╋) in a horizontal or
vertical line. Musketeers move by capturing a (horizontally or
vertically) adjacent piece; the enemy moves by sliding to an empty
adjacent space. The musketeers win if they have no possible moves.