chess.c contains graphics for a chess game.

I haven't written a chess game; when I posted the graphics, Roger Boesch
mentioned that he was working on one, so I'll let him write it and he can
use these graphics if he wants.

draft4.c is a Draughts game by an old friend from Edinburgh University,
Ken Chisholm.  He wrote it in the 70's to reproduce Samuel's checkers, one
of the first self-improving learning games.  The Vectrex game is based on a
non-learning version of Ken's program, because it is to run in ROM and won't
be able to save learned results; also there is not enough RAM to handle
the learning.

I had to modify Ken's program quite heavily to use byte variables whereever
possible and only 2-byte variables for a necessary few objects, in order to
run in the 1K total of Vectrex RAM.

There's a version here that works on linux in text mode, but the main code
here (draft4.c) is now Vectrex-only.  Other files in the directory are parts
of the original code I extracted that may be needed later.

Draft4.c is acting strange at times, I need to resurrect a text-mode version
and play the same game on both, comparing variables until I spot a difference.

Also I'ld like to simulate the parts of the Vectrex interface that are used
in this program (see vectrex.h and controller.h) under X or maybe SDL so I
can run a linux version side by side.

Graham

Now, here are Ken's comments on Draft4:

The Draughts Program Draft4

Draft4 was the fourth version of a Draughts program I had written.

The first version was simply a one move analyser written in FORTRAN
while I was at school, the second version was the same re-written
in algol-60. The third version was an implementation written in Imp
at Edinburgh University which included proper alpha-beta tree search
with pruning and then Draft4 was a major re-write in Imp with rote-
learning by remembering boards and their computed evaluations.

It written to be very portable and so it could run on every computer
in the CS department including the PDP-15, EMAS, the Interdatas and
the PDP-7 with its GT40 display. At the time, which was the mid-
seventies, the cpu speed of a typical processor allowed for about 2
or 3 ply search with a certain amount of hot-pursuit towards stable
board positions which sometimes extended the search to about 6 ply.

Since then it now typically searches to 6 ply in general with hot
pursuit to about 12 ply.

Draft4 was written in 1975 for my undergraduate AI2 project. With
rote-learning of boards, Draft4 quickly learned to play noticeably
better standard openings and end games such as solving the double
corner problem. One novel feature of this learning version was
searching for partial board matches near the end game which worked
quite well due to the relative immobility of draughts pieces.

For example, if it is a double corner standard win on one half of
the board and a win on the other side, such as with all the same side
pieces, it is probably a win overall.

Now of course the Canadian program Chinook has solved Draughts, or
checkers as they call it, using deep exhaustive search and a very
large opening database and end game storage using retrograde analysis.

Ken Chisholm
KJC