How did Google's AlphaZero beat the world's best chess computer?

Google’s AlphaZero, after just four hours of training, last week trounced the highest rated chess engine in the world, Stockfish. How did it do this? 

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AlphaZero: The AI from Google which mastered Chess in 4 hours

Dispatches from the frontiers of chess

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DeepMind's AlphaZero AI beats the world's top board game-playing