Ehresmann

Charles Ehresmann
Charles Ehresmann (right) at the topology conference 1949 in Oberwolfach, together with Paul Vincensini (middle) and Georges Reeb (left)
Born	(1905-04-19)19 April 1905 Straßburg, Alsace-Lorraine, German Empire (today Strasbourg, Alsace, France)
Died	22 September 1979(1979-09-22) (aged 74) Amiens, Picardy, France
Fields	Mathematics
Alma mater	École Normale Supérieure
Doctoral advisor	Élie Cartan
Doctoral students	Jacques Feldbau Georges Reeb Wu Wen-Tsün André Haefliger Valentin Poénaru Daniel Tanré Nguyen Dinh Ngoc
Known for	Ehresmann's theorem Ehresmann connection

Charles Ehresmann (19 April 1905 – 22 September 1979) was a French mathematician who worked in differential topology and category theory. He was an early member of the Bourbaki group, and is known for his work on the differential geometry of smooth fiber bundles, notably the Ehresmann connection, the concept of jets of a smooth map, and his seminar on category theory.

Ehresmann was born in Strasbourg to a family which spoke the Alsatian language; his father was a gardener. He attended school in Strasbourg, then in 1924 went to university at the École Normale Supérieure in Paris. On graduating in 1927 he did one year of military service, and taught at a French school at Rabat in Morocco. He studied further at Göttingen during the years 1930-31, and at Princeton in 1932-34. He completed his PhD thesis entitled Sur la topologie de certains espaces homogènes (On the topology of certain homogeneous spaces) at ENS in 1934 under the supervision of Élie Cartan, and became a researcher with CNRS. From 1935 to 1937 he contributed to the seminar of Gaston Julia, which was a forerunner of the Bourbaki seminar.

Ehresmann was a lecturer at the French University of Strasbourg in 1939, when the German occupation of France irrupted and the whole faculty was evacuated to Clermont-Ferrand. When Germany withdrew in 1945, he returned to Strasbourg. From 1955 he was Professor of Topology in Paris. His post was initially at the Sorbonne, but after the reorganization of Parisian universities in 1969 he moved to the University of Paris VII, Denis Diderot. He also held visiting chairs in Yale, Princeton, Brazil (São Paulo, Rio de Janeiro), Buenos Aires, Mexico, Montreal, and Bombay (Tata Institute); and was awarded an Honorary Doctorate by the University of Bologna. He was President of the Société Mathématique de France in 1965. He retired in 1975.