In $2015,$ Matthew Lai created an AI system called Giraffe that has taught itself to play chess by evaluating positions much more like humans and in an entirely different way from conventional chess$-$playing programs Giraffe$$s level of play is in the top $2$ percent of all tournament chess players. Lai trained his $\_\_\_\_\_\_\_\_$ by adding a random legal move to each position to create greater variety.

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expert system

neural network

deep learning system

computer vision program