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is a game by Christian Freeling. Java applet © 1997 Ed van Zon.

Caïssa is a sort of chess game that was published first on www.mindsports.net. See here for the playing rules. I competed with an own version at the CodeCup 2003. My program is called HIPP and is made in C. You can download a project version and study it. For the calculation of the best move HIPP uses the MTD(f) algorithm. This algorithm uses the constant calling of alfabeta pruning (without memory function) with a so called zero-window search. I have limited the range from the evaluation function from -25 tot 25 to reduce the number of calls. The algorithm is called iteratively to calculated a move one step deeper each time. In the beginning it is not necessary to check for the connection rule and HIPP searches four levels deep. In the end-game the connection rule needs to be checked and HIPP searches for three levels deep. After a quicksort of the possible moves HIPP calculates the best five moves one step deeper. By using a fast generator for moves HIPP finds for each position in the beginning ± 3 million moves. About 30.000 moves are actually executed and 27.000 positions are evaluated. That takes about ± 3 seconds. I have implemented more ideas and I have descibed them in a PDF-document. You can download the document, print and read it. A short summarize:

  1. If in a certain position check is given, HIPP calculates one step deeper from that point because in such a situation the number of countermoves is limited. If in the beginning game two or three moves are available the situation is also calculated one step deeper. Due to this a checkmate situation is found at ten levels deep. In this way I guess that HIPP searches effectively for six to seven levels deep.
  2. The basic idea for the evaluation function is simple and fast: Value= NumberMovesOfMyself - NumberMovesOfOpponent. For this the number of moves from the opponent from the called level is used. I have a big advantage if my opponent is given check!
  3. The first four moves from white and the first three moves of white are calculated in advance. The making of the opening book took about three weeks on a 850 MHz-machine. By calculating the opening moves by more than ten levels deep secures a safe, fast and favourable opening.