After capturing, any piece (not a king) changes colour - white to black or black to white, as appropriate.
A captured unit (not a king) is reborn on its game-array square (R, B and S on the square of the same colour as the capture-square, P on the capture-file). If this square is occupied, the captured unit disappears. A replaced rook is deemed not to have moved for castling purposes. A fairy piece is replaced on the promotion square of the file on which it is captured. If rex inclusiv is specified this means that kings are also covered by the condition. Check is a threat to remove the opposing king from the board - i.e. its rebirth square is occupied.
A captured unit (not a king) is reborn on the unique square 4, 4 away from the square of capture. If this square is occupied, the captured unit disappears. A replaced rook is deemed not to have moved for castling purposes.
A captured unit (not a king) is reborn on the square previously occupied by the capturing piece. In effect, capturer and captured exchange places.
A problem in which all White's moves, at least in the mainplay, are made by the King.
The English Equihopper makes the same number of steps either side of the hurdle, in any direction, can be blocked on any other intermediate square.
A piece (Kings and pawns included) may not move unless attacked by an opposing piece.
Pawns promote on the seventh rank rather than the eighth.
A grasshopper moves and captures on Q-lines by hopping over another unit of either colour (the hurdle) to the square immediately beyond it. A capture may be made on arrival, but the hurdle is not affected.
Black plays first and co-operates with White to enable White to mate Black in the number of moves stipulated. For a helpmate in 2 this means two black moves and two white moves.
If the stipulation is of the form ‘H#n½’ then this means that White starts (this is the half-move) and this is followed by a helpmate in ‘n’ moves. In other words it is a helpmate in n, preceded by a White move.
Black plays first and co-operates with White to enable White to stalemate Black on White's nth move.
A unit (Ks excluded) may not observe a similar enemy unit, with this prohibited even up to capturing the king.
Kamikaze pieces (other than kings) vanish from the board with their victims.
A move is only legal if the moving piece (king, piece or pawn) lands on a square adjacent to a square occupied by another piece of either colour.
A unit other than a King, when observed by an enemy unit of the same kind, is paralysed and may not move, check or capture, but it may in turn paralyse. If rex inclusiv is specified then the kings are included in the condition, which means, especially that they can stand next to each other as each is paralysed and there is no check to either.
The nightrider performs one or more knight-leaps in a straight line as a single move. Thus a nightrider on a1 has access on a clear board to b3, c5, d7, c2, e3 and g4.
The Nonstop (or French) Equihopper makes the same number of steps either side of the hurdle, in any direction, cannot be blocked on any other intermediate square.
No unit (King included) may capture unless it is covered (that is, observed) by a friendly unit. A non-covered unit does not give check (because it can't capture the enemy King).
As selfmate, but with the added provision that if either side is able to mate in one then it must do so.
White is to play and force Black to mate White in the number of moves stipulated. Remember - Black is trying to avoid mating White.
White plays and forces Black to stalemate White in n moves.
Whenever pieces (including kings, but not pawns) move from a square on ranks 2 to 7, they leave behind a pawn of their own colour, unless there are already 8 pawns of that colour on the board.
White plays n moves (with Black not moving until the end of the series) to reach a position where Black is forced to stalemate White immediately.
A captured unit (not a king) is immediately replaced on the square symmetric to the square of capture (which is unique) if that square is empty, otherwise the captured piece disappears as normal. For example, a piece captured on c2 would be replaced on f7. Other examples of pairs of symmetric squares are b7 and g2, a4 and h5, and d4 and e5.
Guarded pieces do not move, capture or check – ie are paralysed.
When in check, kings can move only with the power(s) of the checking piece(s).
U-Chess uses only descriptive notation rather than algebraic. No move may be played unless it can be expressed unambiguously by up to three symbols. This applies, right through to the 'capture' of the black King. The dash, as in P-K4, is not regarded as a symbol, but the 'x' denoting a capture must be counted. Thus PxBP, for example would not be permissable. Only the power of movement is considered when deciding whether a set of symbols in unambiguous. Pins and checks are ignored for this purpose.
A side is in check only if it threatens to capture the opposing king. Checkmate is when such a threat cannot be withdrawn.
Developed and maintained by Brian Stephenson.