I believed to have it too but I checked and I've got the Chess program from PSION instead, which is for the 16kB ZX81. I remember that I lost every single game. I keep it on the old CDs bookshelf, with a cassette of Defender. They're maybe the last two tapes left from those years. The ZX81 is somewhere at my parents house. I also kept the BASIC Programming Manual. I develop with Ruby and JS now, probably no less than 16 MB for any program I run :-)