However, playability has not been determined. Is movement too slow because of the size of the boards? Are the MB rear ranks too open to attack by bishops and queens? Are the AB rear ranks too open to attack by bishops and queens once B's and N's have moved out?
After these rules have settled down, new point values will be needed for the pieces. For example, it appears that bishops gain in strength relative to rooks.
Short version (see the diagram beneath this paragraph)
These rules use six files: a-f. Main boards (MBs) only have files b-e. Only attack boards (ABs) have squares in files A and F.
The ranks are numbered 0-9. The lowest MB has ranks 1-4, the middle MB has ranks 3-6, and the upper MB has ranks 5-8. ABs can have ranks 0 and 9, as well as the other ranks.
Each flat surface is a "level." The MBs are at levels 2, 4 and 6. Each AB is at one of these levels: 1, 3, 5 and 7, which is the highest level.
ABs start the game at levels 1 and 7, at ranks 0 and 9. (NOTE: this is different from some other starting positions for boards based on Star Trek's prop. They place White's ABs at level 3 at the beginning.)
If this description is sufficient, you can skip to Movement
Traditional, two-dimensional chess (2C) has no need to name the board. It is merely "the board." SC has multiple boards, requiring a naming convention. (Foot1) There are two types of boards: fixed (unmovable) boards and movable boards. The three fixed boards are called Main Boards (MBs) and the four movable boards are called Attack Boards (ABs).
Black starts on the high end of the board structure. The highest MB is Black's Defending Board, often simply named "B". The lowest MB is White's Defending Board, also called "W". The middle board is the Neutral Field Board (N).
At the beginning of a game, two of the ABs are placed above the highest MB (B), on the pins farthest from the W board. The other two ABs are placed below W, on the pins farthest from board B. (Foot1)
(Foot1) This is the naming convention shown in the SFTM. For what it's worth, the SFTM does not clearly show whether White's ABs are above or below W at the beginning of the game. Symmetry suggests that White's ABs should be below W, not above. This is different from many other rule sets based on this board structure.
2C has two dimensions: rank and file. SC has a third dimension, made of "levels." A level is defined as the squares in a vertical column, and all share the same combination of rank and file.
2C has a naming convention that uniquely identifies each row of squares, and each square. The row of eight squares at White's end is a "rank" and is assigned the number one. Ranks successively farther from White are assigned consecutive integers from two through eight. A file is a row of squares from one player to the other, and are named with the letters "a" through "h", starting from White's left side. A square is named with its rank and file, e.g. a1 is the closest lefthand square, from White's view.
SC maintains as much of the board position naming as possible. (Foot2) The leftmost possible file is named "a". However, the leftmost file is made of spaces on the left edge of ABs that are at the left edge of MBs - still from White's view. There are only six files. Similarly, the row of squares closest to White - when ABs are positioned as close as possible to White - is rank zero (0). Rows further from White are numbered 1 through 9. In addition to the traditional ranks and files, "levels" are added, and numbered 1 (lowest) through 7 (highest). The MBs are numbered 2, 4 and 6. The ABs can be at levels 1 (White's end), 3, 5 and 7 (Black's end).
Each square has a unique name, whether there is a surface there or not. To the 2C notation, we add the level number, in parentheses. Let's start with some simple examples. At the beginning of the game, White's four pawns on its MB sit on b1(2), c1(2), d1(2), and e1(2). Black's two bishops start the game at c8(6) and d8(6).
The ABs add complexity, partially because of "implied positions" - positions that exist but cannot be used because an AB does not provide a surface for pieces to sit on (but see Vartiation NoGravity1). [Foot2: This rule set adopts Bartmess' board naming convention.]
Two descriptions of movement follow. They should be identical except for details that are best explained in complete sentences. The first description is mathematical, which has the benefit of conciseness and specificity, but its denseness can reduce intelligibility at first. The second is verbose, and easier to interpret.
The table below defines the movements of pieces. "F" means file, "R" means rank, and "L" means level. A piece's movement along a file is indicated by "R=1..7" - the piece may move forward or backward by 1 to 7 spaces. If a piece may move only one space forward along a file, "R=+1". If a piece can only move one level toward the opponent's rear rank, L=+1. If the number of squares moved along a file must equal the number of squares moved along a file, "F=R" is used. If movement along multiple dimensions is required, "&" means "and." "Or" is used to indicate that multiple forms of movement are permitted.
The table uses the notation "(1)" to indicate footnotes. These are used when a brief explanation can provide the small amount of additional information; that detail appears immediately beneath the table.
|P||Move: R=+1 (1)|
Attack: F=R=+1 (2)
|Move: R=+1 (1) or L=+1(3)|
Attack: F=R=+1 (2) or F=L=+1
|B||F=R=1..7||R=1..5 & (F=R or L=R), or F=1..5 & L=F|
|N||R=1 & F=2 or|
R=2 & F=1
|R||R=1..7 or F=1..7||R=1..5 or F=1..5 or L=1..6|
|Q||Moves like a bishop or a rook||Moves like a bishop or a rook|
|K||R=1 or F=1 or F=R=1||R=1 or F=1 or or L=1 or F=R=1 or R=L=1 or F=L=1 or R=F=L=1 (4)|
|AB||N/A||R=3 or F=3 or L=2 (inversion) |
or R=+1 & L=0 (5) or R=-2 & L=0 (6)
or R=-1 & L=0 (7) or R=+2 & L=0 (8)
Pieces move within one board (MB or AB) exactly the same as tradiational chess. Exceptions are described for each piece, below. The traditional rules permitting movement are not limited further in SC, within a board, except for the sizes of the boards.
A pawn may move vertically to an empty square, i.e. change levels, as long as it remains at the same rank and file. A pawn may change one level from an AB to an MB, or from an MB to an AB. If a pawn is changing levels and an AB is "in the way" the pawn can move to it, but may not skip the AB. While changing levels, if an AB is not in the pawn's path, the pawn may skip to the next MB in its vertical path.
A pawn may move forward two squares on its first move.
Examples of pawn movement:
A pawn may attack by moving diagonally - one step forward, one to the side. Additionally, a pawn may attack by moving one step up, and one to the side. The preceding rules regarding pawn movement and ABs apply. For example, a pawn that is on an MB and is changing levels while attacking may skip from one MB to the adjacent MB if there is no AB in the pawn's path.
En passant capture is permitted for attack movements just described. The capturing pawn moves to the position it would have achieved if the pawn being captured had only moved one square.
Initial placement of pawns on ABs severely limits their initial movement. Two exceptions ease this limitation.
An RP is permitted to move diagonally one square, from its AB to the MB to which its AB is attached, landing in front of the nearest N square. Examples include a1(1) to b2(2) (assuming the NP has moved), or f8(7) to e7(6) (same assumption).
Pawn promotion occurs at the furthest rank - 1 or 8 on an MB, 0 or 9 on an AB. The latter includes promotion of a pawn by moving an AB with a pawn to the appropriate position.
Knights move in an "L" shape - either one square in one direction and then two squares in a perpendicular direction, or two and then one. Knights ignore the existence of other pieces when moving, i.e. other pieces do not block the movement of knights. Also, ABs do not interfere with knight movement.
Sample moves include:
Using only MBs:
|b1(2)||c3(2)||Increase file by one, rank by two.|
|b1(2)||d2(2)||Increase file by two, rank by one.|
|b1(2)||b3(4)||Increase file by two, level by one - assuming no AB square exists at b3(3), or that there is no AB square at b1(3).|
|b6(5)||b3(4)||b5(5)||Increase rank by two, level by one.|
|b4(3)||b4(3)||b6(4)||Increase rank by two, level by one.|
A bishop moves in two directions an equal number of squares. A surface is not necessary at intervening squares between the starting and ending points. Examples include:
|c1(2)||e3(2)||Increase rank by 2, file by 2.|
|c1(2)||c3(4)||Increase rank by 2, level by 2.|
Bishops cannot move through occupied squares.
A rook moves in one direction, along a rank, a file, or vertically. A rook may move from one board to another even if an intervening AB is not there.
Rooks cannot move through occupied squares.
Castling: A king and KR on their rear rank may switch places as long as neither has moved. Queenside castling is also permitted if the following conditions are met:
An AB can only be moved by its "owner." At the beginning of the game, each player owns the two ABs that are occupied by the player's pieces. An AB is owned by a player until it is only occupied by one of the other player's piece(s). At that time, the AB is considered "captured" by the owner of the sole piece on it.
Feedback is welcome. Please send questions and comments to jeff<dot>j<dot>victor<at>gmail<dot>com .