Modern chess computers are now largely above the human level. The
chess strenght of Rybka is an estimated 3200 elo (see ssdf and
40/40 rating lists) which has to be compared with the best human
approx. 2800 (the top human, V. Topalov, is rated 2812 in July 08 Fide
list). This state of fact is largely due to a combination of huge
improvements in hardware and software.
The natural question is the following : can we design a game very similar to chess in which the human can beat
the computer ? One proposition is Arimaa. My proposition is
The idea behind Twilight chess is twofold:
- Twilight Chess is really close from standard chess : actually all standard rules of classical chess apply, there is
an addition of two new kind of moves. Hence, good chessplayers, to a large extent, may use their expertise in
- The number of legal moves of twiligh chess is many times the one of classical chess, thus making exploration
much harder for computers. For human there is still this instinct of king-hunting that helps to "understand" a
- The extreme closeness of Twilight Chess and classical makes it almost trivial the transformation of a classical
chess engine into a Twilight chess engine. It is interesting to study the relative impact, in terms of
quality of play, of the new rules for both humans and computers. It could draw interesting discoveries in
The general idea of twilight chess is fairly simple : you can move any of your piece, but the king, into a
twilight zone (warp moves), and any piece on the twilight zone may be moved to any empty square of the board
(drop moves), but pawns on the last rank. More precisely, in a twilight chess game:
It is important to notice that standard laws of chess apply, it answers a lot of questions like
- All classical laws of chess apply.
- Moving to the Twilight zone (Warp move) is a legal moves for all piece but for the King.
- Moving a piece from the Twilight zone to any free square of the chessboard (Drop move) is a legal
chess move but for a pawn into the last rank (8th for white player, 1st for black player).
- Warp and Drop moves are considered as standard moves with relation to classical laws of chess.
- If I drop a Pawn on the first rank (as a white player), afterwards can I move it two squares
forward ? The answer is no since it has already moved (to go into the twilight zone), and moving
two squares forward only apply at Pawns that has not moved yet.
- If I warp and drop a Rook later to its original square can I castle on this side ? The answer is
no because the Rook has moved.
- Mate, stalemate, 50 moves rule etc. behave accordingly.
A new stronger engine, Punica 2.0 has been made by P. Durand. It has been built over the first
engine, Punica 1.0, and interface for twilight chess,
Winboard_TC, have been developped by C. Anzio and A. Barjon. The
engine is a direct modification of
Fruit 2.1. The interface is an adaptation
of winboard, based
on crazyhouse variation. Both software interact through an adapted
version of polyglot.
on Winboard program which is already parameterised. In order to play
to twilight chess, one has to select new variant in the
File menu, and to select Twilight Chess.
If you want sources you can ask me to send you them by
mail me at Frederic.Prost@imag.fr.
Games can be saved and loaded from file using PGN notation. It
is extended in the following way:
Positions can be saved and loaded from file using
FEN notation. It is
extended in the following way: A FEN record contains nine fields. The
separator between fields is a space. The fields are
- Nothing is changed for moves that are neither Warp nor Drop
moves: ie see pgn definition
- Warp move : to move a Quee located on e2 to the twilight zone use "e2@Q" N is for Knight, Q for queen,
R for Rook, B for bishop, P for Pawn.
- Drop move : to drop a Knight in e4 use "N@e4".
- Same as field 1
- List of pieces outside the board. White in upper-case and black
in lower-case letters. If all pieces are on the board then this
field is empty.
- Same as field 2
- Same as field 3
- Same as field 4
- Same as field 5
- Same as field 6
- Integer between 0 and 255. When written in binary this number
indicates whether a pawn has the possibility to move two squares
ahead (since a pawn on the second rank may have been warped and
droped back and in that case it can no longer move two squares in a
row). 1 means that the pawn can move two squares in a row, 0 that it
- Same field as 8th for black.
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