 These programmatic ideas in the theory of knowledge and the philosophy of history were expanded systematically by Windelband’s student Heinrich Rickert (1863–1936). After writing his dissertation (“The Theory of Definition”) under Windelband in Strassburg in 1888, Rickert moved to Freiburg in 1889. The philosophical school became known as the Southwest or Baden school, because Freiburg and Heidelberg are both in Baden in southwest Germany. In 1892, he published The Object of Knowledge (Rickert 1915), which he expanded and modified in subsequent editions over the next thirty years. His most influential book, The Limits of Concept Formation in Natural Science (1st ed: 1902) greatly expands and systematically develops the core idea in Windelband’s essay “History and Natural Science”. His book Das Eine, die Einheit und die Eins (Oneness, Unity, and the Number One, 1911), was one of the few SW works in the philosophy of mathematics.