He edited the letters exchanged between Carl Friedrich Gauss and Wolfgang Bolyai, made contributions to editions of the collected works of Euler and Gauss (for whose works he wrote Gauss als Geometer), and edited the Geometrischen Untersuchungen by Wolfgang and Johann Bolyai (published in 1913).
This individual oversaw the exchange of letters between Carl Friedrich Gauss and Wolfgang Bolyai, contributed to editions of Euler's and Gauss' collected works, and published an edition of the Geometrical Studies by Wolfgang and Johann Bolyai in 1913.