Karel Petr (; 14 June 1868, Zbyslav, Austria-Hungary – 14 February 1950, Prague, Czechoslovakia) was a Czech mathematician. He was one of the most renowned Czech mathematicians of the first half of the 20th century. Biography Petr is known for the Petr–Douglas–Neumann theorem in plane geometry, which he proved in 1908, and was independently rediscovered by Jesse Douglas in 1940 and Bernhard Neumann in 1941. Eduard Čech was a doctoral student of Petr at Charles University in Prague. Petr's doctoral students also included Bohumil Bydžovský and Václav Hlavatý. See also Petr–Douglas–Neumann theorem External links MacTutor Entry (in Czech) 1868 births 1950 deaths People from Kutná Hora District People from the Kingdom of Bohemia Czech mathematicians Charles University alumni Academic staff of Charles University