Phantom Go is a variant of Go for two players and a referee. The players each have their own board, set up so that they can't see the other player's board. The referee has a board of his own. The players play stones on their own board and the referee then copies the move made on his own board, after checking whether the move is legal (i.e. does not try to occupy an intersection on which the opponent has already played or is committing suicide). The referee tells the players what the result of the move was.
If the move could be performed normally he says: 'Black has moved'
If the move was illegal he says 'Illegal move' (but not whether the move was illegal due to a stone already being present or because of the suicide rule).
If the move leads to capture, the referee says 'Black has captured the following stones ...' after which he points out exactly which stones where captured to the White player (and to Black should that be necessary).
To give fair warning to the players the referee also warns when groups are first put into atari.
A snapback sounds like this:
Black plays and puts a white group into atari. White captures one stone and puts himself into atari. Black captures seventeen stones.
For speed, the game is best played on a 13x13 board.
Bill: I have played a form of this game, which we called Kriegspiel Go, after the similar chess variant. The referee only informed the players when it was their turn, prevented illegal moves (the opponent could hear him do that), and removed captured stones. A 9x9 board was large enough. ;-)
Jan: I've also played it that way, but the information about ataris tends to speed up the game and provides some extra confusion... I'm the second best Phantom Go player in Utrecht, by the way :-)
axd:To introduce the concept of fog of war, a variant would require the use of a server delaying moves and information: when a stone is placed, it generates a diamond-like "information ripple" that extends one point per move in all 4 directions with each next move: when such a ripple crosses an opponent group, then only is the opponent shown that stone and becomes visible. (a "ripple" could also be seen as the set of points at the same ManhattanDistance)
Optionally the group to which the played stone belongs might become visible either at once or under influence of the ripple.
The ripple could be delayed for m moves (typically 0) before it would start to spread.
Suicide or playing on a position that is occupied might be forbidden; the resident stone will become visible (optionally: the area within the field of view of the stone) and the opponent will be informed of the tentative.
The "field of view" of stones might be restricted: every stone can "see" only N points (again, ManhattanDistance) far; what happens outside that range is not seen by the player until a stone is positioned to cover the gap. The geometry could be a diamond or a square (or some other shape?).
JoB: Do the players "anounce" their moves, i.e. does the opponent get some idea of a players move or is he completely blind?
The idea is to use a computer (the server) to keep track of who can see what and when. A referee would have a tough time.