Rules

Start: The board is initially empty.

Play: O places one of their pieces at an empty cell then X may elect to swap colours in lieu of making the second move (swap option).
Players then take turns placing a piece of their colour on an empty cell.

Aim: A player wins by connecting three non-adjacent board sides with a chain of their pieces.
A player loses by connecting two opposite board sides with a chain of their pieces (without also connecting three non-adjacent sides).
Each corner cell belongs to both sides that meet there.

For example, the following boards show a game won by O (left) and a game won by X (right). Exactly one player must win every game.

       . . o . . .                 . . o . . . 
      . . . o . . .               . . . o . . . 
     . . . o . . x x             . . . o . . . x
    x x . . o x x . .           . . . . o . x x .
   . . x x o x . . . .         . . . . o x x . . . 
  . . . . x o o . . . .       . . . . x o . . . . . 
   . . . . o x o o . .         . . x x . o . . . .  
    . . o o x . . o o           x x . . o . . . . 
     o o . . x . . .             . . . . o . . . 
      . . . x . . .               . . . o . . . 
       . . . x . .                 . . . o . . 

Syntax

The move syntax is:

    F6       Place a piece at coordinate F6, which must be empty.
    swap   X may elect to swap colours as their first play.

History

Cross rules copyright (c) Cameron Browne 2008.

The Cross rules were originally devised as a game using the Gates tiles that did not favour either player, however it was obvious that the rules constituted a fundamental connection game in their own right. They incorporate a mechanism similar to Yavalath in that players win by achieving a major connection but lose by achieving a minor connection without also achieving the major connection.

Cross is similar to Unlur but simplifies it; both players have identical goals and no extended contract phase is required.

Implementation and help file by Cameron Browne, June 2008.