Chu Chess

Chu Chess is an intermediate between (Mighty-Lion) Chess and Chu Shogi. It was designed for over-the-board play with the aid of two Chess sets, some draughts chips, and an International-Daughts (10x10) board. Pieces placed on a draughts-chip pedestal would represent 'crowned' pieces, i.e. pieces that in addition to their normal Chess moves would also be able to move as an orthodox King. With the exception of the Knight on a pedestal, which would not only get the extra King move, but the full power of a Chu-Shogi Lion. (To highlight its importance, it could be put on top of a stack of draughts chips.) This variant can be played in two versions, differing only in promotion rules, which can be either Chess-like or Shogi-like.

Initial setup f0, e9: King e1, f8: Lion f1, e8: Queen g1, d8: Crowned Rook d1, g8: Crowned Bishop a0, a9, j0, j9: Rook c1, c8, h1, h8: Bishop b1, b8, i1, i8: Knight a1, a8, j1, j8: Commoner a2-j2, a7-j7: Pawns

Moves at a Glance

Click on a piece below to see its moves

											Sliding capture or non-capture, can be blocked on any square along the ray
											Unblockable leap (capture or non-capture)
											Non-capture only
											Capture only
											Captured while passing through the square to another destination

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Piece	ID	value	Moves (Betza notation)	Remarks
King	K	-	K	Can castle with Rook, moving 3 steps towards it
Lion	L	15	KNAD(cK-aK)(K-bK)	Can make two independent King steps per turn (capturing upto two pieces)
Queen	Q	9.5	RB or Q
Crowned Rook	+R	7	RF	aka Dragon Kin
Crowned Bishop	+B	5.25	BW	aka Dragon Horse
Rook	R	5	R
Bishop	B	3.5	B	Color-bound
Knight	N	3	N
Commoner	M	3	K	aka Man or Soldier
Pawn	P	1	mfWcfF	Promotes to Q, R, B, or N on reaching promotion zone

Pawn peculiarities

• Pawns capture differently from how they move (straight move, diagonal capture).
• Pawns can move two squares straight ahead from their initial position, provided they are not blocked.
• On the move immediately after such a double push, they can be captured en passant by another Pawn, as if they had only moved 1 square ahead.
• Pawns promote asthey promote in orthodox Chess piece of choice when they enter the promotion zone (in the Chess-like version).

Castling

A King that has not moved before can move three squares in the direction of a Rook that has not moved before, in which case that Rook is moved to the square the King skipped over. This is only allowed if all squares between King and Rook are empty, when the King is not in check on the square it came from, and would not be in check on any of the squares it skipped over.

General rules

• It is not allowed to expose your King to check.
• The game is won by checkmating the opponent's King.
• Stalemate (no legal moves, but not in check) is a draw.
• The promotion zone is three ranks deep.
• You cannot promote to Lion if you already have one.

Chess-like or Shogi-like promotion

In the Chess-like version only Pawns promote. You can choose what piece to promote to, but promotion is mandatory: you cannot stay a Pawn. In the Shogi-like version other pieces can also promote, but there is no choice: pieces promote to their 'crowned' versions, and acquire the moves of a King on top of their own that way. Pieces that already had all King moves cannot promote. Thus a Commoner cannot Promote, and a Pawn can only promote to Commoner. The Knight promotes to Lion, and thus gains unusually much in value.

The Lion piece

The Lion can make two moves per turn. That means it can also capture two pieces per turn, one on the square it moves to (as normal), and one 'en passant' on the transit square. It can also capture on the transit square, and move on to an empty square ('hit and run'), or capture and move back to where it came from ('shooting' the piece from a distance, as it were). Of course it can also capture a single piece in the normal Chess manner. In that case the transit square is immaterial.

The Lion can make such double moves as two King steps, i.e. in all directions, and arbitrarily changing direction between them. It can also jump over the transit square, i.e. reach the distant two-step destination in a single jump. Finally it can also just make a step to an adjacent square, refraining from taking a second step.

Restrictions on Lion capture

There are rules to make Lion trading very difficult, in order to keep the Lions in play. Basically they specify that two Lions cannot be captured in consecutive half-moves. When the first capture is Lion x Lion from a distance, it is forbidden to play it if pseudo-legal (i.e. without taking account of check) recapture of the capturing Lion is possible with another piece than King. So even when the Lion is protected only with a pinned piece, the other Lion cannot capture it from a distance, just like a King could not capture it.

When a non-Lion captures a Lion, it is just the other way around: then the 'counterstrike' by a non-Lion against the Lion is forbidden. One possibility left open is thus when you capture an adjacent Lion. But then you would in general be foolish to allow recapture, as you could take the Lion hit-and-run fashion, fleeing to a save square. An exception to the rule is when a valuable opponent piece (i.e. not a Pawn) forms a 'bridge' between the Lions; you may then capture that piece in the first leg of the double-move, and then take the opponent Lion with the second leg. Then the opponent can recapture, but he will have lost a valuable piece. In the late end-game, when you have nothing to protect your Lion with other than King, trading becomes possible.

XBoard interface issues

This game has to be played with the option Show Target Squares on! This option will cause marking of the target squares of any piece you select or grab, by the engine (with legality testing off) or by XBoard (legality testing on). Moving to a square marked in cyan will be interpreted not as the final destination, but as the transit square after the first step of a multi-leg move. XBoard will then highlight the possible destination squares of the second leg from there. Should you want to end on the cyan square, you click it again, (it will be no longer marked in cyan), and XBoard will terminate the move after the first leg. You can also move back to the starting square, to 'shoot' the opponent piece from nearby.

XBoard will allow both the Chess-like and the Shogi-like promotion; the engine will have to decide which promotion style it thinks legal. The default choice in 'sweep-promotions' mode will be deferral for pieces, however, to facilitate Chess-like play. To play a Shogi promotion in this mode you should enter it as a click-click move, but during the click on the promotion square move the mouse pointer down until the promoted piece appears, and only then release the mouse button. The Pawn will show Queen as default, and a 'dragging click' on the promotion square will cycle through all choices. In the Shogi version you would have to choose the Commoner that way. With a promotion popup you would have to press 'No' on piece moves into the zone when you play the Chess-like version, and press 'Commoner' on Pawn promotions when you play the Shogi-like version.

Differences with FIDE

The board is 10x10, with a 3-rank-deep promotion zone. The initial setup leaves an almost empty rank behind the pieces, where you can immediately castle. You have a Lion, Crowned Rook, Crowned Bishop and two Soldiers as extra pieces. In the Shogi-like version of the rules, some pieces other than Pawn can also promote.

Strategy issues

It is not possible to force checkmate on a bare King with just a single Bishop or Knight (in addition to your own King). Two Knights cannot do that either.

With a single Commoner you can force checkmate on a bare King.

Bishops are confined to squares of a single color. Having Bishops on both colors compensates this weakness, and is worth an extra 0.5 on top of their added value.

A Queen is upward compatible with all weaker pieces except Knight. So only promotion to Queen or Knight makes sense, (except perhaps for rare situations where you might have to avoid stalemate).