What's the simplest mind sport in the world? Go? No, people can't even agree on the rules of that. Tic-Tac-Toe? Simple, but you really need some paper to draw the board. I Spy? Well, it requires something to spy. We claim the world's simplest mind sport requires absolutely no equipment whatsoever - merely two players, each with one hand. Even then, if the players don't have hands, they could probably improvise.

The simplest mind sport in the world is rock-paper-scissors. It's known by different names all around the world, most famously Roshambo - phonetic French for "rock-paper-scissors", didn't you know? - "Muk-Chee-Bah" in Korea and "jun ken pon" in Japan, but the game remains the same. Upon a count of three, people make one of three gestures - rock (clenched fist), paper (flat palm extended towards the opponent) and scissors (first two fingers extended towards the opponent). Rock breaks scissors, scissors cuts paper, paper wraps rock.

Game theorists have analysed rock-paper-scissors and come to the conclusion that the optimal way to win a game of rock-paper-scissors is to play completely randomly; random play will win as many throws as it loses and hence draw every match. However, consider trying to win a tournament by drawing every match!

Therefore, when trying to win a rock-paper-scissors tournament, you should assume that players will be trying to win the whole event and hence will not be playing optimally. Therefore you shouldn't play optimally - instead, you should figure out how to play in order to beat your opponent. When played face-to-face, psychology becomes a major factor, simply because humans are poor at producing genuinely random numbers. He's not going to throw rock again... surely? The pastime has some popularity among poker players and hardened gamblers who will bet on anything.

The natural progression from this was a World Championship; the gambling nature of the game dictated there can be no better location for it than Las Vegas. Whether this makes rock-paper-scissors the new chess or chess the new rock-paper-scissors is open to debate.

Interest in man vs. machine mind sports spreads worldwide and sportwide, so it's probably inevitable that someone had the bright idea of programming a computer to play rock-paper-scissors and seeing if it could exploit humans' poor randomisation skills in order to win against human opposition at the game. Then more and more people approached the task, each looking at it from a slightly different angle, and this was the result.

Last year, Darse Billings, a researcher at the highly-rated University of Alberta, organised The First International RoShamBo Programming Competition; thirty-nine authors, from ten different countries, submitted a total of 45 different entries which took part, added to ten dummy robots, each with a conceptually simple strategy. After all, "Tit for tat", although incredibly simple, proved to be the best strategy in the Prisoner's Dilemma - for further details, see the comprehensive, scholarly and detailed description of the game in the Stanford Encyclopedia of Philosophy - so who's to say that something just as simple and predictable wouldn't work as well in this?

The competition was fierce and attracted entries from some extremely well-respected names within the world of artificial intelligence and games engine programming - not least Dr. Jonathan Schaefer, author of Chinook, the draughts program which became the first computer program to beat all human opposition, even world champions, in a game of skill. Several of the other University of Alberta researchers took part too, plus Jason Hutchens, winner of the first ever Loebner Prize (earned by victory in a "Turing Test" contest, where each program produces natural language output and tries to be indistinguishable from humans in conversation with judges). The second ever Loebner Prize winner was one David Levy, now one of the Board of Directors of the MSO. It seems that the techniques required to teach a computer to speak natural language and to teach a computer to play ruthless rock-paper-scissors aren't too different.

However, the strongest entries came from a group of alumni of the California Institute of Technology who worked on the problem, including such distinguished names as Wei-Hwa Huang, four-time individual winner of the World Puzzle ChampionshipS. Second place went to Jakob Mandelson for his computer program Phasenbott and the overall champion was Iocaine Powder, written by Dan Egnor. Another member of that group, Joshua Schachter, submitted the program which, while trying its best to win, finished last overall by an impressively long margin, which was at least as remarkable a result as the victory - in terms of magnitude, if not direction.

Many of the best entries have made their source code public, and future similar rock-paper-scissors programming contests are planned. David Levy, of the MSO Board of Directors, ran the Computer Olympiads between 1989 and 1992 - in effect, the Mind Sports Olympiad where all the participants were computer programs - and is reportedly keen to revive the project, possibly as part of MSO IV. Who knows, perhaps the world's simplest mind sport of them all, rock-paper-scissors, might make an appearance?