To play Expacon choose a version on your left. Instructions and demos are provided for each version.

Expacon is a new and very challenging game which grew out of a part of modern algebra called group theory. Group theory has many uses, in particular in the design and understanding of patterns and consequently in cryptography. The famous British mathematician Turing used group theory to help unravel the messages encoded by a machine called Enigma, which was developed by the German military in the Second World War. Various symbols can be used in writing down these messages, and decoding these messages often involves manipulating strings of these symbols, subject to certain rules. This gives rise to a game, which we have called Expacon, which involves Expanding and Contracting such strings of symbols. One starts out with an initial string of symbols, an additional collection of symbols, which we refer to as Rules, and an end string of symbols. The goal of the game is, by a succession of moves, to transform the intial string into the end string. Each move is the addition, insertion or deletion of Rules into strings already obtained, and so is the result of expansion or contraction of strings. Hence its name, Expacon.

At the present time, November 25, 2009, Expacon is undergoing some revisions. However, there are many games available to be played. They are arranged as follows:

When you begin playing Expacon and click on a version to play, say a circle version, the first games that come up for you to play are dated July 17. Using the green arrow key in the forward direction will take you through the games dated July 17 and then through the games 1,3,4,5,6,8,9 to April 9, then April 22 and through the following dates.  At one point, the games are out of order. Please forgive this awkwardness.

We hope you enjoy the challenge provided by Expacon, despite these slight problems in the organization of the games. There are also  a number of games, referred to as Challenge Games for the most accomplished players.