Karel Petr

Karel Petr (1868 to 1950) was a Czech mathematician born in Zbyslav in Bohemia, then part of Austria-Hungary, who spent his career at Charles University in Prague. He took his doctorate there in 1897 with a dissertation on semi-invariants under Frantisek Josef Studnicka and Frantisek Kolacek. He is known for the theorem in plane geometry that now bears the names of Petr, Douglas and Neumann: he proved it in 1905 in Czech and again in 1908 in German, and it was rediscovered independently by Jesse Douglas in 1940 and by Bernhard Neumann in 1941. He was also a teacher of consequence, and his doctoral students included Bohumil Bydzovsky, Eduard Cech and Vaclav Hlavaty. Petr died in Prague in 1950.