This is a CLIPS (http://clipsrules.sourceforge.net/) rule based system that plays white king-rook against black king chess endgame. To start a game, after loading chess.clp, use (start-game). Playing is pretty self-explanatory. The idea is not to do extensive search but use as humane rules as possible. Indeed, search goes as deep as 2 half-moves at worst (mate situations) without even looking at all possible moves and rules are pretty close to how an average player would reason in such a simple endgame. Understandably, not always does the system find optimal move that leads to fastest mate. However, most often it finds some at least good enough move. There is a parameter ?N which determines size of board. As far as tested, it always manages to checkmate on boards bigger than 5x5. However, it's been mainly tested on 8x8. Very few of the functions have side effects. Realization has obvious weaknesses like different rules computing same results in LHS and even rules that invoke same functions in LHS and RHS. However, at least on 8x8 board, performance is not a problem.