Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The M. Riesz extension theorem is a theorem in mathematics, proved by Marcel Riesz during his study of the problem of moments. Marcel Riesz (November 16, 1886 September 4, 1969) was a Hungarian mathematician who was born in Gy r, Hungary (Austria-Hungary). He moved to Sweden in 1908 and spent the rest of his life there, dying in Lund, where he was a professor from 1926 at Lund University. He was known for work on classical analysis, on fundamental solutions of partial differential equations, on divergent series, Clifford algebras, and number theory.