1. American Mathematical Society,The Leroy P. Steele Prizes, Internet page: http://www.ams.org/secretary/prizes.html#steele.
2. American Mathematical Society, 1991Mathematics Subject Classification, Internet page: http://www.ams.org/msc/.
3. Nicolas Bourbaki,Eléments d’histoire des mathématiques, Hermann Editeurs, 1969.
4. Britannica CD-97, Encyclopædia Britannica, Inc., 1997.
5. Rodrigo De Castro,Sobre el núméro de Erdős, Lect. Mat. 17(1996), 163–179.