Retractor is a program for Retrograde Analysis chess problems. In retrograde analysis chess problems, one is given a position and asked to deduce some historical information about it, such as what the last n moves were, or where a particular piece was captured, etc. A large number of retrograde analysis problems can be found at the link above.

To aid composers and solvers of retro problems, Retractor allows one to set up a position and play backwards from it. It checks for common illegalities to rule out many illegal moves. Retractor also has the capability to solve some retro problems of the "Last n moves?" variety. To determine legality of positions, Retractor detects conditions such as illegal checks and also calculates and uses a variety of information such as:

Retractor also allows the user to specify that a particular side made no captures or no promotions, or to specify the number of promotions that occurred on a particular square. This information is then used by Retractor and will aid Retractor in both the solving and the interactive mode.

Retractor is useful to both the beginning retro solver, who can benefit from the tutorial included and the immediate feedback on illegal moves, as well as the experienced retro enthusiast who will enjoy the benefits of being able to explore the retrovariations of a position on the computer.

The current version of Retractor is 1.0. It is currently available only for Windows.

To download Retractor 1.0 (162K zip file), click here.

Here is the README included with Retractor, with instructions on how to install it and notes on getting started with it. Note: The web address for the Retro Corner contained in the program is outdated. The correct address is in the first paragraph of this page.

Retractor was developed by Chad Whipkey and Theodore Hwa as a Senior Project in the Department of Computer Science at Stanford University.