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Caïssa
Caïssa can no longer be played in the ArenA, but you can still
the applet.
In the initial position the board is covered with 49 tiles. During play this number is bound to be reduced.
- All play is on the tiles
- White begins. Players move, and must move, in turn
The connection rule
The tile-complex must remain connected, that is, a tile or group of tiles must always
remain orthogonally or diagonally connected to the rest.
The Queen
The king's role is played by the Queen. The diagram on the left shows its options for movement and capture
in a non-check situation. If in check, it is restricted to adjacent squares, as shown in the diagram
on the right. Thus pieces giving check from a distance, need no cover!
The Queen is the only piece with the power of capture in the usual sense.
The Atlantis effect
If the Queen moves, the tile it vacates is removed in the same turn. The removal is compulsory,
but it may not violate the connection rule.
The mutual check rule
The mutual check rule: Queens may not see one another along the same rank, file or diagonal,
so neither player may effectuate that situation.
Thus a Queen may protect a piece against capture by it's counterpart.
The Pieces
The pieces move as in Chess. Under the implicit condition of not putting its own Queen in check
and the explicit condition of not violating the connection rule, a piece can always move to
any of its target-squares, whether or not it is tiled, and if it is, whether or not it is occupied,
and if it is, regardless of the color of the occupying piece!
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If the target-square has no tile, the piece takes its own tile with it.
At the end of the move the tile-complex must still be connected. There is no 'during the move',
so the Knight in the diagram below may legally move to the square marked A.
Moving to B is of course illegal
- If the target-square has an empty tile, the piece may simply move there
- If the target-square is occupied by a friendly piece, the player must exchange the pieces
- If the target-square is occupied by an opponent's piece, the player must also exchange the pieces,
but there is one exception: a switch between two pieces of the same type may not in the next turn be
'undone' by the opponent
The necessity of the last rule should be obvious. It represents a
situation similar to the one that gave birth to the 'ko' rule in the game of Go.
The mate in 1 below shows another application of tile-surfing and the connection rule.
For clarity all other pieces have been omitted. After d2c4, the Queen cannot move because the tile on c1
would be disconnected. Of course if black were able to exchange the knight on c4 immediately with any of his pieces,
he could yet prevent the mate, but the queen would remain immobile for the moment.
(The only way to liberate the Queen after an exchange of the knight on c4, would consist of moving a piece,
and thus a tile, to any of the squares b1, c2, d1 or d2, leaving the critical tile on c1 connected if
the Queen would move).
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