In 1895 at the University of Rostock he received his Promotion (Ph.D.), summa cum laude, under the supervision of Otto Staude[2] with dissertation entitled Über eine Gattung n-fach periodischer Functionen von n reellen Veränderlichen.
Inspired by Sophus Lie, he wrote "On transformation groups, all of whose subgroups are invariant" (Hamburger Math Society Vol 4, 1902).
His predecessors were the great Jacques Ozanam in France, where the number theorist Édouard Lucas (1842–1891) in the 19th century wrote similar books, and Walter William Rouse Ball (1850–1925) in England (Mathematical recreations and essays 1892), Sam Loyd (1841–1901) in the U.S. and Henry Dudeney (1857–1930) in England.
In this sense Martin Gardner (1914-2010) and Ian Stewart, the editor of the math column in Scientific American, might be regarded as his successors.
Names of living mathematicians are rarely met with, but references to the "old masters" such as Abel, Euclid, Euler, Gauss, Helmholtz, Lagrange, Laplace, Steiner, and Weierstrass, are very numerous.The whole constitutes a most admirable piece of work and must long serve as a desirable model for works of like nature.