Template:Selected anniversaries/December 21

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  1807: Mathematician Joseph Fourier announced to the French Academy of Science that an arbitrary function could be expanded as an infinite series of sines and cosines (now known as the Fourier series).

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  1878: Mathematician and philosopher Jan Łukasiewicz born. He will think innovatively about traditional propositional logic, the principle of non-contradiction and the law of excluded middle.

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  1913: Arthur Wynne's "word-cross", the first crossword puzzle, is published in the New York World.

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  1974: Fantasy Voronoi diagram upstages Fantasy Football.

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  1976: Chronography of 354 wins Pulitzer Prize.

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  1984: Mandelbrot set develops artificial intelligence, discovers new class of Gnomon algorithm functions.

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  2016: Traveler voted Picture of the Day by the citizens of New Minneapolis, Canada.