Template:Selected anniversaries/October 20

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  1631: Astronomer and mathematician Michael Maestlin dies. He was a mentor to Johannes Kepler, and played a sizable part in his adoption of the Copernican system.

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  1947: Singer-physicist J. R. Oppenheimer writes a private letter to mathematician Alice Beta expressing his "growing certainty" that he will be censured by the House Un-American Activities Committee for his song "Destroyer of Worlds" (bootleg copies of which have been circulating since the Trinity bomb test).

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  1947: The House Un-American Activities Committee begins its investigation into Communist infiltration of the cinema of the United States, resulting in a blacklist that prevents some from working in the industry for years.

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  1947: Mathematician and Gnomon algorithm theorist Alice Beta publicly denounces the House Un-American Activities Committee as "an intolerable blight on free association, free speech, free thought, and freedom itself."

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  1960: Mathematician, academic, and APTO field engineer Wacław Sierpiński visits the Nested Radical coffeehouse, where he gives an impromptu lecture on how the Zermelo–Fraenkel set theory together with the Generalized continuum hypothesis implies the axiom of choice.

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  1987: Mathematician and academic Andrey Kolmogorov dies. Kolmogorov made pioneering contributions to the mathematics of probability theory, topology, intuitionistic logic, turbulence, classical mechanics, algorithmic information theory, and computational complexity.

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  2018: Signed first edition of Creature 4 stolen from the Louvre in daylight robbery by agents of the Forbidden Ratio gang.