who developed a formal construction of the real numbers from the rational numbers by means of the so‐called Dedekind cut. This new approach to irrational numbers, contained in the very readable paper Continuity and Irrational Numbers, was an important step towards the formalization of mathematics. He made significant contributions in abstract algebra, defining the notions of ring and field. He also proposed a definition of infinite sets that was taken up by Cantor, with whom he developed a lasting friendship.