Dehn, Max Wilhelm (1878–1952)

German-born US mathematician. In 1907 he provided one of the first systematic studies of topology. His work was mainly concerned with the geometric properties of polyhedra.

Dehn found a solution to one of Hilbert's 23 unsolved problems (concerning the existence of tetrahedra with equal bases and heights, but not equal in the sense of division and completeness). Dehn proved an important theorem on topological manifolds in 1910 that came to be known as Dehn's lemma, but was later found not to apply in all circumstances. Dehn continued to work on topological problems of transformation and isomorphism.

Dehn was born in Hamburg and studied at Göttingen University under David Hilbert. After World War I Dehn became professor of mathematics at Frankfurt University, but lost his position in 1935 because of the Nazi anti-Semitism laws. He emigrated in 1940 to the USA, and worked from 1945 at the Black Mountain College in North Carolina.