Io is a territory game featuring othelloanian capture and the 'one-bound-one-free' opening protocol to get to one of its zillions of initial positions.

io position Rules
There are two players, Black and White. Each has a sufficient number of stones and both move only with their own color.

Capture
Io features 'othelloanian capture'. Generally speaking it means that if a placement results in one or more opponent's stones that lie in an unbroken straight or diagonal line, to be enclosed between the placed stone and a like colored stone at the other end, then these stones are captured and reversed in the same turn, to reveal the moving player's color.

The diagram shows a 9x9 board. Beginners may benefit from using a 7x7 board.

The one-bound-one-free phase
White starts by placing one stone on the empty board. From that point on players take turns to:

  • Place a stone on a cell straight or diagonally adjacent to the last stone placed by the opponent, and ...
  • ... place a stone on a on a cell that has only vacant cells, straight or diagonally, as neighbors.
  • In this phase a corner may only be occupied with the first or bound placement.
  • Both placements are compulsory. When the player to move can no longer make the second placement, then his turn ends and his opponent may start the single placement phase.

Note: the diagram shows a board position at the end of the first phase. White's last free move was at C1. Black's bound reply was at B2 to keep E1 for free placement. Thus White is forced to make a bound move (F2) and leave the first move in the next phase to Black. If Black had chosen D1 or D2 for his bound placement, there would have been no place for a free placement, and White would have had the first move of the next phase.

Capture in the one-bound-one-free phase
By the nature of the protocol, capture with a free move is not possible. Capture with a bound move follows the normal othelloanian protocol. Because of captures, the number of stones of each color may not be the same at the end of this phase, though the number of placements of both sides will always be the same.

The single placement phase
Now players take turns to compulsory place one of their stones on any vacant square. Corners are no longer excluded. If a placement results in capture, then the normal othelloanian protocol is followed.

Object
The game ends when the board is full. Winner is the player with the most stones. Draws are not possible.