Fichtenholz, Gr. M. "Sur la notion de fermeture des systèmes de fonctions"(PDF). In: Proceedings of the International Congress of Mathematicians in Toronto, August 11–16. 1924 (in French). Vol. 1. p. 686. Archived from the original(PDF) on 1 December 2017. Retrieved 30 November 2017.
Fichtenholz, Gr. M. "Sur la notion de fermeture des systèmes de fonctions"(PDF). In: Proceedings of the International Congress of Mathematicians in Toronto, August 11–16. 1924 (in French). Vol. 1. p. 686. Archived from the original(PDF) on 1 December 2017. Retrieved 30 November 2017.