On the 4x4 board below, two white and two black queens are placed so that no queens of one color attack any queen of the other color.
Find a way to place 9 white queens and 9 black queens on an 8x8 chessboard in a similar fashion.
(In reply to
re: No Subject by Dej Mar)
Yes! Thanks for the Graphic. There are probably quite a few unique (i.e. not just rotational) solutions. The main theme seems to be to clump the queens together, so collectively they attack as few squares as possible. We do not need to worry about the second color, but only placement of nine queens so that nine squares are not under attack: placing the second color on those will satisfy the "mutual" aspect since the states of attacking and being under attack are symmetrical.
re(2): No Subject
