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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  1916: Time-travelling physician-warrior Asclepius Myrmidon arrives during a artillery barrage in western Europe, sets up emergency field hospital.

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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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  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. He made significant 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.