Copyright (c) 1977 T.Truran

This game is played on an empty 5x5 square board:

There are 24 white and 24 black stones off board (or just 24 Othello stones).

  • DROP PHASE - At each turn, each player must drop a friendly stone on an empty cell, except the central cell which should be empty until this first phase is over.
    • When 24 stones are dropped, the game continues with the move phase.
  • MOVE PHASE - At each turn, each player must do one of the following actions:
    • Move a friendly stone to an orthogonally adjacent empty cell.
      • There are custodian captures, i.e., every enemy stone between the moved stone and another friendly stone (over the same line) switches color.
      • After a move with results in a capture, the moved stone may optionally move again into its initial cell (which may result in more custodian captures).
    • If a player cannot move any stone, he should pick one friendly stone on any cell and drop it on the empty cell, executing the eventual custodian captures.
  • GOAL - A player who has only four stones or less, loses the game.

There are the possibility of cyclic positions (check the second example). To handle those cases, there are, at least, these options: (a) it is invalid to repeat a previous position (however, this super-Ko rule may be hard to check); (b) declare a draw if a cycle is found; (c) it is invalid to have N consecutive moves without captures (say N=4).

An example

Black's turn. Since he cannot move, he must drop a stone at a5. Black moves a2-a5, capturing the white stones at a4 and b5.

Then White must move a1-a2 (its only valid move). Then Black may move b1-a1 (capturing a2) and then, since he made a capture, he moves back to b1 (capturing c1).

After that move, Black win the game, since White only has four stones left.

A cyclic example

Black's turn.

If you try to play this position, you will find that the board repeats itself after six moves!

I wish to thank Julián R. of Madrid for this game information.