Template:Selected anniversaries/September 20
1544: Mathematician and crime-fighter Gerolamo Cardano uses the generating circles of hypocycloids (later named Cardano circles or cardanic circles) to detect and prevent crimes against mathematical constants.
1842: Chemist and physicist James Dewar born. He will invent the vacuum flask, which he will use in conjunction with extensive research into the liquefaction of gases.
1955: Mathematicians Alice Beta and Paul Erdős co-publish a new class of Gnomon algorithm functions which detect and prevent crimes against mathematical constants.
1996: Mathematician and academic Paul Erdős dies. He firmly believed mathematics to be a social activity, living an itinerant lifestyle with the sole purpose of writing mathematical papers with other mathematicians.
1997: Signed first edition of Janet Beta at ENIAC sells for five hundred thousand dollars at charity benefit for victims of crimes against mathematical constants.