🕸Fergus Duniho wrote on Sat, Nov 12, 2022 08:43 PM UTC:
Here are the rules of Chess66 as I've written them up for Game Courier. Apart from a change to the naming convention for the new spaces, is this complete and fully accurate? Note how I've divided this into five sections. These are the geometry of the board, the difference that Switches make, how spaces in a Switch count as separate spaces, how spaces in a Switch are sometimes treated as the same space, and how the individual pieces move.
Rules of Chess66
Chess66 is an adaptation of Chess to a board with a different geometry. Where no difference from Chess is noted, it follows the rules of Chess.
Its board has two extra spaces that each overlap with a neighboring space and push the rank it is on over by half a space. A4 overlaps with a4, pushing the 4th rank half a space right. H5 overlaps with h5, pushing the 5th rank half a space left.
Because its ranks and files no longer line up neatly on a Cartesian grid, movement is based only on geometrical relations and not on the coordinate system.
Lateral movement is allowed through the sides of spaces, and lateral movement in the same direction goes through the opposites sides of spaces. Because of this, vertical movement may sometimes shift the file named by the coordinate system.
Diagonal movement is allowed through the corners of spaces that do not share any sides, and diagonal movement in the same direction goes through the corners at opposite ends of spaces.
A Switch is a pair of overlapping spaces that come together at one end and branch off at the other. In doing so, they allow some new movement options:
At its narrow end, each space in a Switch shares the same side with an adjacent space. This allows a Rook or Queen to move through the narrow end to one of two different files. In this way, a Rook or Queen can checkmate a King without assistance from another piece.
From the broad end, a Rook or Queen can move through the Switch to the same file, providing a new way for double attacks to work.
Also at the narrow end, each space in a Switch shares a corner with another adjacent space that neither one shares any sides with. Through this corner, diagonal movement is able to change color. So, a Bishop that moves to A4 or to H5 may move away on a subsequent turn on a different color. This allows Bishops to switch color, giving a Bishop the power to reach every space on the board.
Although the two spaces in a Switch overlap, they count as separate spaces.
A piece moving to a Switch must move to one space or the other. For example, a Pawn on a2 can make a double move to either A4 or a4.
While some paths can lead to either Switch, others lead to only one space or the other in a Switch. For example, a Bishop on e8 can go to A4 or h5, and a Bishop on d1 can go to a4 or H5.
The movement options available to a piece on a Switch depend upon which space of the Switch it is on. For example, a Pawn on A4 can proceed only to a5, and a Pawn on a5 can proceed only to b5. Also, a Bishop on A4 can move away on either light or dark spaces, but one on a4 can move away only on light spaces.
Because the two spaces in a Switch overlap, they are treated as the same space in some respects:
The two spaces in a Switch cannot be occupied simultaenously.
It is illegal to pass through a space in a Switch if the other space is occupied.
A piece may move to a space in a Switch only if both spaces in it are empty or one is occupied by an enemy piece. If a piece moves to the empty space in a Switch, and the other space is occupied by an enemy piece, that piece is considered captured.
It is not legal to move from one space in a Switch to the other. Instead, A4 is treated as though it were horizontally adjacent to b4, and H5 is treated as though it were horizontally adjacent to g5. This affects the movement options for Rooks, Queens, Kings, and Knights
King
The King leaps one space in any lateral or diagonal direction. It may castle with a Rook on its first move so long as it is not in check, there is nothing in between it and the Rook, it doesn't pass through check while castling, and the Rook hasn't moved. In castling, it moves two spaces toward the Rook, and the Rook moves to the space the King passed over.
Queen
The Queen may move as a Rook or a Bishop.
Rook
The Rook may move any number of spaces in any lateral direction until it reaches an occupied space or Switch.
Knight
The Knight can leap directly to any space that could be reached in two one-space moves except for those reachable by two in the same direction. Since a piece on A4 or H5 can move directly to b4 or g5, a Knight on one of these can leap further away than a Knight can normally leap.
Bishop
A Bishop may move any number of spaces in any diagonal direction until it reaches an occupied space or Switch.
Pawn
The Pawn may move one space straight forward without capturing, or it may move one space diagonally forward to capture. On its first move, it may move two spaces forward without capturing so long as it isn't blocked. If this move takes it over a space an enemy Pawn could have captured it on, that Pawn may immediately capture it by en passant, moving to the space it passed over. On reaching the last rank, it must promote to another piece. This may be any piece except a King or another Pawn.
Here are the rules of Chess66 as I've written them up for Game Courier. Apart from a change to the naming convention for the new spaces, is this complete and fully accurate? Note how I've divided this into five sections. These are the geometry of the board, the difference that Switches make, how spaces in a Switch count as separate spaces, how spaces in a Switch are sometimes treated as the same space, and how the individual pieces move.
Rules of Chess66
Chess66 is an adaptation of Chess to a board with a different geometry. Where no difference from Chess is noted, it follows the rules of Chess.
A Switch is a pair of overlapping spaces that come together at one end and branch off at the other. In doing so, they allow some new movement options:
Although the two spaces in a Switch overlap, they count as separate spaces.
Because the two spaces in a Switch overlap, they are treated as the same space in some respects:
The King leaps one space in any lateral or diagonal direction. It may castle with a Rook on its first move so long as it is not in check, there is nothing in between it and the Rook, it doesn't pass through check while castling, and the Rook hasn't moved. In castling, it moves two spaces toward the Rook, and the Rook moves to the space the King passed over.
The Queen may move as a Rook or a Bishop.
The Rook may move any number of spaces in any lateral direction until it reaches an occupied space or Switch.
The Knight can leap directly to any space that could be reached in two one-space moves except for those reachable by two in the same direction. Since a piece on A4 or H5 can move directly to b4 or g5, a Knight on one of these can leap further away than a Knight can normally leap.
A Bishop may move any number of spaces in any diagonal direction until it reaches an occupied space or Switch.
The Pawn may move one space straight forward without capturing, or it may move one space diagonally forward to capture. On its first move, it may move two spaces forward without capturing so long as it isn't blocked. If this move takes it over a space an enemy Pawn could have captured it on, that Pawn may immediately capture it by en passant, moving to the space it passed over. On reaching the last rank, it must promote to another piece. This may be any piece except a King or another Pawn.