Johannes Hjelmslev

Johannes Trolle Hjelmslev was a Danish mathematician from Horning who lived from 1873 to 1950 and worked in geometry and the history of geometry. He was born Johannes Trolle Petersen and took the surname Hjelmslev to avoid confusion with Julius Petersen, although some of his results, such as the Petersen-Morley theorem, still appear under his original name. He discovered the Hjelmslev transformation, a method for mapping an entire hyperbolic plane into a circle of finite radius. His publications include a doctoral thesis on infinitesimal descriptive geometry from 1897, textbooks on descriptive geometry and geometry for the Polytechnic College in Copenhagen, a study of natural geometry, a book on the foundations of projective geometry, and historical work on the Danish mathematician Georg Mohr. He was the father of the linguist Louis Hjelmslev.