What is Co Neutron?

A B C D E +---+---+---+---+---+ Black's -> 1 | x | x | x | x | x | 1 back row +---+---+---+---+---+ 2 | | | | | | 2 +---+---+---+---+---+ 3 | | | * | | | 3 +---+---+---+---+---+ 4 | | | | | | 4 +---+---+---+---+---+ White's -> 5 | o | o | o | o | o | 5 back row +---+---+---+---+---+ A B C D E x = Black pawn * = Neutron o = White pawn

Co Neutron is played by 2 players on a 5x5 square board. The players sit on opposite sides of the board. One plays white (or "Oh"), the other plays black (or Eks). The row closest to the player's side is their back row.

We can see here the starting position, along with the coordinate system for the notation. For example, the Neutron is starting on square C3.

How do I win?

A game of Co Neutron can be won in 2 ways:

• a player moves the neutron to their OPPONENT'S back row
  • or forces their opponent to move it there;
• the opponent cannot make a complete turn.
  • (usually this means the neutron is trapped and can't be moved).

Moving

The players take turns. All pieces move in exactly the same way, in a straight line in one of the eight possible directions, and they must go as far as possible. Specifically, they must travel in a straight line until they bump into another piece, or the edge of the board.

A complete move consists of moving first the neutron, then one of your own pieces.

On the initial setup, this means the neutron can go to either A3 (straight horizontal line to the left), B2 (straight diagonal line up and left), C2, D2, E3, B4, C4 or D4. It can NOT stop at B3 because it has to be moved until it reaches the side of the board or runs into another piece! The pawns are moved in the exact same way: in a straight line, and as far as they can go.

Notation

The moves are notated by designating the start/end squares of the Neutron and the pawn. Optionally the start square for the Neutron can be omitted, as it's implicit.

So if White's first move is to move the neutron to A3 and the pawn on B5 to B2, it is notated as 'C3-A3,B5-B2' or 'A3,B5-B2'.

Optionally the punctuation may be omitted.

If the neutron can be moved (or is forced to be moved) in a way that ends the game (meaning: finishing on a back row), then only the neutron move has to be notated: 'A5'.

Acknowledgements

A Co Neutron tournament was run at Cambridge University by Mark Owen and Julian Richardson. They had modified the rules of Neutron to make it more balanced, and so are the inventors of Co Neutron.

So what is Neutron?

Neutron is pretty much identical, except that the aim is to get the Neutron to your own back rank. That means that you want to get your pieces off your back rank as fast as possible, both to create the openings for the Neutron, and to use the pieces to shepherd it. Neutron is so unbalanced it has two inelegant kludges.

• On the first move only a pawn is moved;
• For their second move, the second player may choose to change sides.

Quotation from Tim Berners-Lee