Burr puzzles background information

The following pages contain some background information about burrs. The information is not nearly as complete as we would wish, partly because it is very difficult to get at the information and partly because we did not have time to write down everything we know. But this is a start, and you can always check back here to see if we have made any progress and added more information.
A Historical overview gives a short introduction to the relatively few known facts about the roots of burr puzzles.
The Definitions section contains a rigorous collection of definitions used in the following sections. A few simple Lemmas are also introduced to show some trivial conclusions following directly from the definitions.
The Three-piece burrs are the simplest possible burrs. That is - they have the fewest number of rods possible. However, there are no regular three-piece burrs possible. This section explains why, and shows some non-regular designs to build a three-piece burr after all.
Six-piece burrs are the most common burrs. This section introduces previously published material as well as new insights gathered from our own work.
The Bibliography lists books, articles, and other web-sites which were used to start our research into the area of burrs. There are not many such publications, and few of them deal exclusively with burrs.