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Help For Neutron


Welcome to the network Neutron server. The rules of Neutron are below. The commands are the same for all pbmserv games.

neutron challenge userid1 userid2 [ -size=number ]
Start a new game between userid1 and userid2.
The -size option can be used to set the board size to any odd number greater than or equal to 5.



The Game of Neutron

Neutron was invented by Robert A. Kraus and published in issue 71 of the excellent English Magazine Games & Puzzles. The structure of Neutron is familiar, but it has several unusual twists.

Neutron is a two-player game played on a 5x5 square board; White owns the five white pawns at the bottom of the board and Black owns the five black pawns at the top of the board. The neutron begins in the center and doesn't belong to anybody. Figure 1 shows the board at the beginning of the game. Notice the coordinates used for recording moves.

                 A   B   C   D   E
             1 | x | x | x | x | x | 1 <- Black's back row
             2 |   |   |   |   |   | 2
             3 |   |   | * |   |   | 3
             4 |   |   |   |   |   | 4
             5 | o | o | o | o | o | 5 <- White's back row
                 A   B   C   D   E

        x = Black pawn  o = White pawn  * = Neutron

              Figure 1.  Beginning of Neutron.

Winning the game is simple; just maneuver the neutron onto your own back row. It doesn't matter if you move it there yourself or if you force your opponent to do the deed for you. As soon as the neutron shows up on your back row, you've won the game. You can also win by stalemating your opponenet. That is, if your opponent gets trapped in a situation where he cannot complete his turn, you've also won the game. Each turn has two parts and it is easy to lose because both parts must be completed before the turn is legal.

White always plays first and the turn alternate -- White, Black, White, Black, ... . As I said above, a turn has two parts. First the player moves the neutron; then he moves one of his own pawns. Now it is a little easier to see how a stalemate might occur. If Black can trap the neutron sorround it completely with with pawns -- then White will not be able to complete even the first part of his turn and so will lose the game. There is one exception to the two part turn rule. On White's very first turn only, White does not move the neutron. This helps even out the advantage White gets from moving first.

Every piece, even the neutron, moves in excactly the same way -- along a straight line horizontally, vertically, or diagonally. A piece stops moving just before it runs into another piece or the side wall; there is no jumping or capturing. But there is one unusual feature. When a piece moves, it must go as far as possible in the direction chosen. There is no stopping short. For example, White's pawn which begins on B5 can go to A4, B2, or E2, but it cannot stop on B3 or C4. Neutron pieces are a lot like politicians; they aren't smart enough to stop when they're ahead.

Just to make sure you understand the game, why don't you try to answer there questions about Figure 2? First, where can White's pawn on C5 move to? Second, what squares can Black's pawn on B4 move to? Third, can White win if it is his move? Finally, can Black win if it is his move? There are answers at the end of the coloumn, but don't peek right away.


                 A   B   C   D   E
             1 |   |   | x |   | o | 1 <- Black's back row
             2 | x | o |   |   |   | 2
             3 |   |   | * |   | o | 3
             4 | x | x | x |   |   | 4
             5 |   |   | o |   | o | 5 <- White's back row
                 A   B   C   D   E


             Figure 2.  A sample game.

Neutron Notation

To be able to record a game a notation has to be introduced: When moving pieces the move is recorded as the coordinates of the source and the destination. The coordinates are separated by a dash (-). In figure 1 three legal moves exists for the white pawn at B5. They are: B5-A4, B5-B2, and B5-E2.

When moving the neutron the source is know and is omitted (along with the dash). In figure 2 the following 5 moves are valid for the neutron A3, C2, D2, D3, and D4.

The first move only involves moving a white pawn and is recorded as just described.

The next moves are a combination of a neutron move and a pawn move. They are also recorded as just explained and are separated with a comma (,). For example: "A2,C4-E2".

The last move may be terminated after moving the neutron to a back row and thus does not need the move for a pawn. For example: "C1" or "E5".


  1. A5, D5, D4.
  2. A5, B5, A3, B3.
  3. White moves the neutron to A3 and his pawn on E3 to B3. Now White wins because Black is stalemated. Using the Neutron Notation this can be written as "A3,E3-B3".
  4. Black moves the neutron to A3 and the pawn on A2 to B3. Now White must move the neutron to A1 giving Black the win. Black could also move his pawn from C4 to B3 to stalemate White. In short, either "A3,A2-B3 A1" or "A3,C4-B3".


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