Retrograde Analysis is a genre of chess problems where the legality of the position is a key element. A position is legal if it can be reached through a legal chess game (no matter how weird). On the Retro Corner you will find more than 3500 Retro problems, a glossary, and much more Retro related stuff.

First of all, many thanks to Philippe Schnoebelen for starting and maintaining the Retrograde Analysis Corner for years. The Retro Corner is currently maintained jointly by Joost de Heer and Otto Janko.

 G. Husserl Prize, Israel Ring Tourney, 1966/71 Here one of the two Ks is in double check by Rd8 and Qc6. The only possible explanation is that the last move was -1.c7xd8=R+. Thus we conclude that Rd8, Qc6 and Kd6 are White; Kc8 is black. Then further impossible checks are avoided by setting Ne8 and Rf6 White; Pb7 Black. A black Pb7 entails that Ba8 is promoted, so that Ba8 and Pa7 are White.The last move was c7xNd8=R+ because only a Nd8 gives Black something to retract. Solution 0+9. Color the pieces. What was the last move?

## Recent updates of the Retro Corner

### October 6th, 2019

Two new Articles:

• 50x50 Problem [by Nikita Michailowitsch Plaksin, 1979]
• On the Tracks of Chess Pieces [by Alexander Kislyak, 1998]

## Problems from Retro Columns in Chess Magazines

Many problems are provided with solutions, however, there are several problems of which I don't have a solution. You can contribute if you have a solution not present here.

Retrograde Analysis is a genre of chess problems where the legality of the position is a key element. A position is legal if it can be reached through a legal chess game (no matter how weird).

Retros (i.e. problems with a Retrograde Analysis content) may ask for e.g. a mate in two, but the main content (at least in modern Retros) is in explaining the history of the position. Part of it anyway. This is essentially a matter of logical reasoning, with high appeal for puzzle enthusiasts.

(I'd like to offer a real tutorial here. Maybe in the near future... In the meantime I have just collected a few examples with high pedagogical value. Hope this will convince you that retro puzzles are fascinating. Hope it will start some vocations!)

Many introductory texts exist. For complete beginners, the Sherlock Holmes book by Raymond Smullyan is a very good, exhilarating, easy-to-find start. After this, you can have a taste of the real modern retro-analysis by looking at Fabel's Introduction to Retrograde Analysis. Many shorter introductory texts exist.

## My Aims with this Web Site

(by Philippe Schnoebelen)

I'd like this page to be a repository where all retro-enthusiasts can find easy access to material pertaining to Retrograde Analysis. (Discussions and interactions are better carried through the Retro Mailing List.)

I started this in April 1995. I am a chess player & casual retro-problems solver who finds it difficult to get access to current problems. They are quite scarce. A magazine with a retro column only publishes a few problems.

Reading the rec.games.chess USENET newsgroup, I discovered that there are many potential retro-fans on the Net. It seems many computer scientists are really enthusiastic about retrograde analysis when they have the opportunity to encounter some nice retro-problems. Many have enjoyed reading Smullyan's Sherlock Holmes book and would like more of the same stuff. (The problems from Smullyan's book can be found on Otto Janko's German pages)

I believe it is possible to make some of these problems available here on the Web. This will be beneficial for solvers and for composers. Indeed, as the artist he is, every composer is willing to reach the largest possible readership. Here people will find many current retros (with the necessary explanations when required).

I hope many retro-beginners here on the net will actually send their solutions and comments to retro-columnists. Believe me, this is a great motivation for looking in earnest at the problems, and the greatest tribute that can be paid to the composers and columnists. Many problems are exhilarating and not too complicated. (Anyway, you don't have to solve all of them!)

## A Gallery of Retro Masterworks

Here will be found collections of the best retros ever composed. Suggestions for additions are welcome.

## Some Retro Sources

Of course, the main sources for retro-material are the retro-columns of chess magazines. The retro-corner tries to survey some of them in its Retro columns section.

Yet another source is the

Much more complete bibliographies about retros and chess-maths problems exist elsewhere, e.g. the one maintained by

## Join the Retro Mailing List

There exists a mailing list <retros(at)janko.at> where many retro-enthusiasts discuss retro problems, exchange puzzles and comments, ask questions and help find cooks in newly published originals. It is a powerful source of information because many people from different backgrounds participate.

The list has a very good signal/noise ratio and traffic usually fluctuates in between 2 and 30 messages per week. Try it!

You can subscribe (and manage your account) at

and visit the mail archive at

## Acknowledgements

Many many many people already contributed to The Retrograde Analysis Corner by

• commenting and suggesting,
• sending original & classical retro-problems,
• surveying current retro-columns,
• pointing out errors, omissions, typos,
• answering Questions left open in some places,
• sending missing solutions to miscellaneous problems,
• completing miscellaneous lists,
• posting warm praises and thanks and advertising the page!

The Retrograde Analysis Corner would not be so rich without them. It is even safe to say that, without them, it would have stopped after a few weeks. I cannot give proper credit to all these people but I will try to maintain a list of all people who contributed, from one-shot contributors to enthusiasts who never stopped sending information and advices.

I hope that starting this list in April 1996 will not make me miss too many names in retrospect. Many apologies to whoever I forgot to include.

## History

The Retrograde Analysis Corner was started at

• http://cosmos.imag.fr/CONCUR/phs/Retros/RetroCorner.html

by Philippe Schnoebelen and then maintained at

• http://catv6081.extern.kun.nl/~retro/RetroCorner.html

by Joost de Heer for many years. Now it's hosted by Otto Janko at

• https://www.janko.at/Retros/index.htm

and maintained jointly by Joost de Heer and Otto Janko.

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The quite large material that has been gathered in these pages originates from a large set of benevolent contributors, who spent their time and energy in the interest of the Retro community. We make it a question of principle that

Copying any part for commercial use is prohibited!

Copyright (c) 1996-1999 by Philippe Schnoebelen
Copyright (c) 2000-2001 by Joost de Heer
Copyright (c) 2002-2016 by Joost de Heer and Otto Janko