Template:Selected anniversaries/December 21
From Gnomon Chronicles
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).
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.
1913: Arthur Wynne's "word-cross", the first crossword puzzle, is published in the New York World.
