SCHUR, ISSAI (Isaiah ; 1875–1941), mathematician. Schur was born in Mogilev, Ukraine. In 1920 he became professor of mathematics at the University of Berlin. He specialized in the theory of numbers, particularly with regard to finite groups and their representations. He is widely known as the author of "Schur's lemma," which states that the only operators that commute with a unitary irreducible representation are the scalar multiples of the identity operator. Schur is also credited with extending the finite group theory to compact groups and is noted for his work in the representation theory of the rotation group. With the rise of Nazism he emigrated to Ereẓ Israel, where he lived until his death.
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