Fix '3 knights' bug + tiny advance on problems tab

[vchess.git] / views / rules / Ultima.pug

p.boxed
	| Most pieces look the same but behave very differently.
	| They generally move like an orthodox queen,
	| but capturing rules are complex.

h3 Specifications

ul
	li Chessboard: standard.
	li Material: "standard".
	li Non-capturing moves: often like queen.
	li Special moves: none.
	li Captures: very special.
	li End of game: standard; see below.

h4 Pieces names

p Pieces names refer to the way they capture, which is described later.
ul
	li Pawn : pawn or pincer
	li Rook : coordinator
	li Knight : long leaper
	li Bishop : chameleon
	li Queen : withdrawer
	li King : king (same behavior as in standard chess)
p.
	Besides, a new piece is introduced: the immobilizer, represented by the letter 'm'
	in FEN diagrams and PGN games. It is represented by an upside-down rook:

figure.diagram-container
	.diagram
		| fen:8/8/4m3/8/8/8/3M4/8:
	figcaption Immobilizers on d2 and e6.

h3 Non-capturing moves

p
	| Pawns move as orthodox rooks, and the king moves as usual,
	| one square in any direction.
	| All other pieces move like an orthodox queen.

p.
	When a piece is adjacent to an enemy immobilizer, it cannot move unless
	the enemy immobilizer is adjacent to a friendly immobilizer or chameleon
	(cancelling the powers of the opponent's immobilizer).
p
	| Note : this corresponds to the "pure rules" described on 
	a(href="http://www.inference.org.uk/mackay/ultima/ultima.html") this page
	| , which slightly differ from the initial rules.
	| The aim is to get rid of the weird suicide rule by weakening the immobilizers lock.
	| In particular, in the original rules two adjacent immobilizer are stuck forever
	| until one is captured. Note that it's still the case if all chameleons disappeared.

h3 Capturing moves

p
	| Easy case first: the king captures as usual, by moving onto an adjacent square
	| occupied by an enemy piece. But this is the only piece following orthodox rules,
	| and also the only one which captures by moving onto an occupied square.
	| All other pieces capture passively: they land on a free square and captured
	| units are determined by some characteristics of the movement.

p Note: the immobilizer does not capture.

h4 Pawns/Pincers

p.
	If at the end of its movement a pawn is horizontally or vertically adjacent to an
	enemy piece, which itself is next to a friendly piece (in the same direction),
	the "pinced" unit is removed from the board.

figure.diagram-container
	.diagram
		| fen:7k/5ppp/2N5/2n5/3rB3/8/PPP5/K7:
	figcaption 1.Pc2c4 captures both coordinator and long leaper.

h4 Coordinators (rooks)

p.
	Imagine that rook and king are two corners of a rectangle (this works if these
	two pieces are unaligned).
	If at the end of a rook move an enemy piece stands in any of the two remaining
	corners, it is captured.

figure.diagram-container
	.diagram
		| fen:8/2b4K/2q5/3p1N1p/8/8/2R5/k7:
	figcaption 1.Rc5 captures on c7 and h5.

h4 Long leapers (knights)

p.
	A knight captures exactly as a queen in international draughts game: by jumping
	over its enemies, as many times as it can/want but always in the same direction.
	In this respect it is less powerful than a draughts' queen:
	on the following diagram c8 or f6 cannot be captured.
	However, the knight does not have to maximize the number of captured units
	(as is the case in draughts).

figure.diagram-container
	.diagram
		| fen:2n4k/3r4/5b2/3p4/1m6/3b4/3N4/K7 w d4,d6,d8,a5:
	figcaption All marked squares captures are playable from d2.

h4 Withdrawer (queen)

p.
	The queen captures by moving away from an adjacent enemy piece, in the opposite
	direction (only the long leaper can jump).

figure.diagram-container
	.diagram
		| fen:7k/8/8/3Qr3/8/8/8/K7 w a5,b5,c5:
	figcaption 1.Qa5, 1.Qb5 or 1.Qc5 captures the black rook.

h4 Chameleon (bishop)

p The chameleon captures pieces in the way they would capture. So, it
ul
	li pinces pawns,
	li withdraws from withdrawers,
	li leaps over long leapers,
	li coordinates coordinators.
p ...and these captures can be combined.

figure.diagram-container
	.diagram
		| fen:7k/8/8/r3pP2/2n5/8/B7/K7 w a5,c4,e5:
	figcaption 1.Bd5 captures all marked pieces.

p.
	Besides, chameleon immobilizes immobilizers (but cannot capture them since they
	do not capture).

p.
	A chameleon captures the king in the same way the king captures, which means that
	a chameleon adjacent to a king gives check.

h3 End of the game

p.
	Checkmate or stalemate as in standard chess. Note however that checks are more
	difficult to see, because of the exotic capturing rules. For example, on the
	following diagram the white king cannot move to the marked squares because then
	the black pawn could capture by moving next to it.

figure.diagram-container
	.diagram
		| fen:7k/8/8/p4r/4K3/8/8/8 w e5:
	figcaption 1.Ke5 is impossible

h3 Credits

p.
	A good starting point is the 
	#[a(href="https://en.wikipedia.org/wiki/Baroque_chess") Wikipedia page], 
	which also gives pointers to other interesting pages (including chessvariants.com,
	as usual).