Help For Amoeba

Introduction

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

amoeba challenge userid1 userid2 [ -small ] [ -single ] [ -promote ] [ -opponent ]

Start a new game of Amoeba between userid1 and userid2. There are several options, which are explained in detail in the rules below, but here is a brief summary of each:

The -small option starts a game on a smaller 7x7 board.
The -single option restricts squares from sliding more than 1 space.
The -promote option allows pawn to promote only on the very last rank of the board.
The -opponent option allows you to slide squares which are occupied by your opponent's pieces.

Rules of Amoeba

Amoeba is a chess variant played on an 9x8 board with 64 squares. Eight of the spaces are empty and adjacent squares may slide into the empty spaces, thus altering the shape of the board.

The -small variant is played on a 7x7 board with 38 squares and eleven empty spaces.

This is the initial layout of the normal Amoeba board:

      a   b   c   d   e   f   g   h
    +---+---+---+---+---+---+---+---+    
  9 |*R*|*N*|*B*|*Q*|*K*|*B*|*N*|*R*|  9
    +---+---+---+---+---+---+---+---+    
  8 |*P*|*P*|*P*|*P*|*P*|*P*|*P*|*P*|  8
    +---+---+---+---+---+---+---+---+
  7 |:::|   |:::|   |:::|   |:::|   |  7
    +---+---+---+---+---+---+---+---+
  6 |   |###|   |:::|   |:::|###|:::|  6
    +---+---+---+---+---+---+---+---+
  5 |:::|###|:::|###|###|   |###|   |  5
    +---+---+---+---+---+---+---+---+
  4 |   |###|   |:::|   |:::|###|:::|  4
    +---+---+---+---+---+---+---+---+
  3 |:::|   |:::|   |:::|   |:::|   |  3
    +---+---+---+---+---+---+---+---+
  2 | P |:P:| P |:P:| P |:P:| P |:P:|  2
    +---+---+---+---+---+---+---+---+    
  1 |:R:| N |:B:| Q |:K:| B |:N:| R |  1
    +---+---+---+---+---+---+---+---+    
      a   b   c   d   e   f   g   h

This is the initial layout of the -small Amoeba board.

      a   b   c   d   e   f   g
    +---+---+---+---+---+---+---+    
  7 |###|*R*|*N*|*K*|*N*|*R*|###|  7
    +---+---+---+---+---+---+---+    
  6 |###|*P*|*P*|*P*|*P*|*P*|###|  6
    +---+---+---+---+---+---+---+
  5 |:::|   |:::|   |:::|   |:::|  5
    +---+---+---+---+---+---+---+
  4 |   |:::|###|###|###|:::|   |  4
    +---+---+---+---+---+---+---+
  3 |:::|   |:::|   |:::|   |:::|  3
    +---+---+---+---+---+---+---+
  2 |###|:P:| P |:P:| P |:P:|###|  2
    +---+---+---+---+---+---+---+    
  1 |###| R |:N:| K |:N:| R |###|  1
    +---+---+---+---+---+---+---+    
      a   b   c   d   e   f   g

Movement

Each move in Amoeba consists of two parts. The first is a normal chess move. The second part is optional, and consists of sliding a square horizontally and/or vertically to an empty space.

All pieces move the same as in regular chess, with the following exceptions:

Pieces may not move through or land on an empty space, although Knights may jump over them.
There is no en passant capture.
In the small version only, pawns do not get an initial 2-space move.

Sliding Squares

When sliding a square, any of your own pieces which are on the square slide with it. You may not slide squares which are occupied by your opponent's pieces. Squares may slide horizontally or verically through any number of contiguous emtpy spaces, including around corners. (The -single option will restrict squares to moving a single space, and the -opponent option will allow sliding your opponent's pieces.)

A square cannot be slid back to the same position it occupied before the most recent turn by the opponent. This is the "ko rule" for sliding squares. For example, if your opponent slides the square at a2 into the empty space at b2, you may not slide it back to a2 on the following turn. You must wait a turn before you may do so, or if there was another empty space nearby, such as at b3, you could slide it to there.

Pawn Promotion

Pawns promote when they reach the last non-empty space which exists in their column. In other words, if there are no squares (just empty spaces) in front of the pawn, it promotes.

Pawns always promote at the end of the turn of the player who owns the pawn. This means that a pawn does not promote if it moves to a promotable position and then slides to a non-promotable position in the same move. It also applies to the rare event when you slide a square out from in front of one of your opponent's pawns, placing it in a promotable position. In this case the pawn does not promote until the end of the opponent's next move. It is possible to set up a position in Amoeba where 3 pawns can promote in the same turn.

If the "-promote" option is used, pawns only promote when they reach the last very rank of the board.

On the -small board, pawns may promote to rook, knight, or bishop, but NOT to a queen.

Check and Mate

Check and Checkmate only only considered at the end of a turn. So it is legal for a king to move into check, as long as the check is removed by sliding a square. (Slide the king out of check, slide the attacker to a different position, or leave an empty space between the attacker and the king.)

Differences between Amoeba and Eight-Stone Chess

Eight-Stone Chess is Amoeba with the empty spaces represented by stones on the board. Since it uses stones instead of holes, players may want to use the -promote option to disable early promotions. It restricts most stone moves to single spaces, but it allows a special move of a stone from one end of a straight line of stones to an unoccupied square at the other end. The -single option would prohibit this special move, so it is best for players to agree on restricting themselves to a subset of the allowed moves before starting the game.