4k specific rules
The size of the engine is limited to a maximum of 4KiB (4096 bytes).
At entry this should be an executable or a script and consist of only 1 file.
The file name should not contain information; engines.json options if used to contain part of engine will be counted towards size with irrelevant characters removed (example: "TuringEngine":"...."). Hash, Threads and any such configuration option not used to bypass size reduction is not counted towards size in any way.
Startup should be within 60s and not leave itself any files lying around, not counting what system programs might cache.
Explicitly allowed external commands: bzip2, bash, c++, cargo, cc, clang, chmod, gzip, lzma, mktemp, perl, python, python3, pypy3, rustc, sh, sleep, tail, xz.
Explicitly allowed libraries: Various system libraries like libc, also CUDA and OpenCL. For python Numpy allowed.
If python-chess library is used, it must be included in the binary and thus counted toward the size.
Commands and libraries not listed in either of above might later be allowed and added to allowed list, by discretion of the organizers.
At least the following subset of the UCI protocol must be supported: go or go wtime A btime B winc C binc D, isready, position startpos (moves ..), uci, ucinewgame and quit
Authors can use UPX or some other executable packer or self decompressing shell script.