FAQ for Dead Reckoning
Q1. What is Retrograde Analysis?
A1. Retrograde Analysis (retro) is a genre of tricky chess problems focusing on the legality of the position. "A position is legal if it can be reached through a legal chess game (no matter how weird)." (That's taken from the excellent Retrograde Analysis Corner, which is the basic online intro to the field.) So these problems are like detective stories: you're trying to look at the evidence to figure out what's happened. They can be quite fun: and at the top end can be extremely challenging to design and solve. This site contains a lot of different chess problems, with particular focus on the theme of Dead Reckoning.
Q2. What is Dead Reckoning?
A2. A weird thing happened. I stumbled across a chess rule that no one knew about before. No, really. The International Chess Federation updates the Laws of Chess every few years. Obviously, they don't change the key stuff: like how a bishop moves. But they do fiddle around at the margins, and in 1997 they introduced a rule which has little impact on the real game, but does have consequences for chess problems. It wasn't until late 2000 that anyone noticed these consequences. It happened to be me.
Q2. What is Article 5.2b?
Q4. What kind of positions are amenable to Dead Reckoning analysis?
A4. More than you might think. About 200 different retrograde problems have been composed to date. These fall into three basic classes of position, corresponding to different reasons why a position might become dead, to wit:
But in fact, it's can also be used for forward stipulations, problems where there's no Retrograde Analysis at all.
Q5. What does the text below the diagrams mean?
A5. This is the stipulation. Almost all of it is standard notation & terminology used by most chess problem enthusiasts. A quick summary follows, divided into three sections. The main activity asked by the stipulation may be forward or retro. A forward activity may nonetheless require retro analysis (e.g. is that e.p. legal?). A novelty of DR is that to determine the history of the game, reasoning about the future is often required!
GENERAL ELEMENTS OF A STIPULATION
COMMON FORWARD ACTIVITIES
COMMON RETRO ACTIVITIES
Q6. How do you know from the diagram whether a possible castling or e.p. capture is legal?
A6. There are default conventions on castling and en passant which help you decide whether a player is allowed to castle or capture e.p. in an ambiguous position, where one doesn't know the precise history of the game. These conventions apply by default even if nothing mentions them in the stipulation. However, these conventions simply don't affect most of the Dead Reckoning problems, here, since Dead Reckoning itself is there to disambiguate the positions.
The default castling convention says that (given a certain player to move in a forward stipulation) castling is permitted unless it's provably illegal. If you castle, then obviously you can assume for purposes of any retro analysis that the castling must have been legal. If you don't castle, then you can't make any assumption either way. In the case of mutually exclusive castling, the first one to do so gets away with it, and excludes the others.
The default en passant convention says en passant is permitted only if you can prove it's legal: i.e. that the immediate prior move was the relevant Pawn double step. If you don't capture, then you can't make any assumptions for retro purposes that the en passant was legal or illegal.
There are two other conventions which are not default, and would usually be indicated by an acronym in the stipulation: RV overrides the default conventions, and says that every possible legal combination of castling and en passant rights must be considered as a separate problem. AP extends the default conventions, and says that en passant is legal if justified by a later castling move which would only be legal if the e.p. was legal. (If this last one sounds weird, you are right.)
Q7. Where are the solutions?
A7. Various places. Published articles have solutions associated with them. Small DR diagrams can be clicked to expand to a larger diagram for ease of viewing, and these below these diagrams are links to solution pages, which are being updated gradually to cover all the DR positions. There is also still an answer file accessible from the home page which gives the minimal answer without explaining anything.
Q8. What do "DR Illegal" and "DR Restricted" mean?
A8. A position with a specified person to move is DR Illegal if only under A1.3 is illegal. A position with a specified person to move is DR Restricted if only under A1.3 is there a unique last move.
Q9. The new stuff looks very different from the old stuff on this website. What's going on?
A9. I am in the middle of reorganizing. The "What's new?" area points to the new format that I will be using, and I will gradually adapt all the older material to this kind of approach. But the older material remains logically consistent. Please tell me what you like and what you don't like, not just in terms of content but also for style and organization.
For new compositions, I'm using one gif image per composition, and many compositions/page. Earlier I was using one gif image per square, and assembling 64 images to make one board/page. The larger older images are still visible: if you click on a smaller DR diagram it will expand. Try this one:
Grouping related images by page make senses, but several experiments with jigsaw technology for smaller diagrams have not given me satisfactory results, so I am using single images. I estimate that each board image takes perhaps a second to download on a 58k modem, so is probably acceptable for most users.
The main problem now is the quality of the smaller images. The original EPD2DIAG gif images are shrunk on the fly from 314x314 to 180x180. I am looking for a tool which will allow me to generate directly good single board gifs with size approximately 180 pixels. Any suggestions welcome.
These grouped images are probably easier for printing, but I should say that I have not yet looked at putting in pages breaks at the right point. This is not something which HTML does very well.
Q10. Is that all there is here?
Thanks for your time.