Artificial intelligence: Go master Lee Se-dol wins against AlphaGo program 2016-03-11

Lee Se-dol, one of the world's top players, said his win against AlphaGo was "invaluable".

The Chinese board game is considered to be a much more complex challenge for a computer than chess, and AlphaGo's wins were seen as a landmark moment for artificial intelligence.

A fifth game will be played on Tuesday.

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Go is thought to date back to several thousand years ago in China.

Using black-and-white stones on a grid, players gain the upper hand by surrounding their opponents pieces with their own.

The rules are simpler than those of chess, but a player typically has a choice of 200 moves, compared with about 20 in chess - there are more possible positions in Go than atoms in the universe, according to DeepMind's team.

It can be very difficult to determine who is winning, and many of the top human players rely on instinct.