- Set Theory, maintained by Jean Larson (Mathematics, University of Florida)
- Articles by J.J. O'Connor and E.F. Robertson, in The MacTutor History of Mathematicsarchive, (Mathematics, University of St. Andrews):
- A Homepage for the Axiom of Choice, maintained by Eric Schechter (Mathematics, Vanderbilt University)
- Gödel's Incompleteness Theorem, maintained by Dale Myers (Mathematics, University of Hawaii)