The 
board is divided into exactly one hundred spaces, each
of which borders on a number of spaces of the opposite color.
A space is said to ``border on'' another space if the two spaces share
a common side. Spaces sharing only a single common corner do not
border on one another. In particular, the center of the board itself
is a corner rather than a space.
As a consequence of this definition and the coloring conventions for spaces, any unfilled (white) space will border only on filled (black) spaces, and any filled space will border only on unfilled spaces.