The game is played with identical disks that are
coloured white on one side and black on the other.
One player takes black, the other white. They take
place a disk in their colour, and make a custodial entrapment of disks
colour. All disks that are caught within an entrapment
are turned over to show their opposite colour. The aim is to have the
majority of the disks in your colour
at the end of the game. Black goes first.
If a player cannot make an entrapment of at
least one of the opponent's colours then he misses a go. If
neither player may make a move, or when all the squares are occupied,
the game is at an end.
Position. A game starts with the four centre
squares occupied in the following configuration.
Starting position. )
A custodial entrapment occurs when you place a disk in
your colour so that a line of your opponent's colours is flanked by
your colour at both
ends. Entrapments can be either in an orthogonal or diagonal direction.
In the following diagram if Black plays at 'A' the marked disks
will be reversed.
Before and after. )
entrapments can be made.
All disks caught in an entrapment have to be reversed.
Multiple entrapment. Before and after. )
You cannot use the edge of the board to trap. The triangled
disks in the following diagram will not be reversed. One consequence of
this is that a disk in the corner can never be reversed.
( Before and
after. A line of edge-connected disks is not reversed. )