Last-modified: 2010-11-25 (木) 22:00:30
- The derived set of a subset S of a topological space is the set of all limit points of S.
- Kelley, John L.,General topology. 2nd ed. (English) [B] Graduate Texts in Mathematics. 27. New York - Heidelberg - Berlin: Springer-Verlag. XIV, 298 p