[1] He proved the first version of the splitting theorem.

He was also known for his collaboration with David Hilbert on the 1932 book Anschauliche Geometrie, translated into English as Geometry and the Imagination.

[2] He was born in Breslau (then a city in the Kingdom of Prussia; now Wrocław in Poland).

He wrote a 1924 doctoral dissertation at the University of Breslau (now the University of Wrocław) under the supervision of Adolf Kneser.

He was barred from lecturing in 1933 under Nazi racial legislation, because he was Jewish.