The precursor to Su Doku was invented in 1783 by Leonhard Euler, a Swiss mathematician. After many years in obscurity, the puzzle was copied in America then picked up in Japan, where the format was further altered. Wayne Gould, a former judge from New Zealand, saw its potential and designed a computer program to devise new versions. It was Gould who, with The Times, brought the game to Britain.

Given Su Doku’s elaborate path to fame, the idea behind it does not appear to be owned by any one person or company, although some people may own some rights in the game. Failure to obtain the best protection for puzzles that go on to achieve great success is not uncommon: the first Rubik’s cube was not adequately protected in the UK as Erno Rubik had no money for international patents and had to fall back on registered design and other rights.

Since versions of the Su Doku puzzle have been played for hundreds of years, it is unlikely that any one person can prevent another from using the format to devise puzzles. Any protection obtained by Euler would long since have expired, putting his work into the public domain. For anyone else now to seek a patent, that would have to be limited to his own developments, which would need to be “new” at the date on which protection is sought (ie, not yet published) and also inventive over other known variants of the puzzle.

Since the puzzle has been in the public domain for so long, the name Su Doku is now probably also in the public domain and cannot be monopolised by one provider any more than one could monopolise the name “crossword”. So it is essential that anyone devising new games or puzzles consider the following protection.

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