## Quick Reference

A mathematical theory originated by the Russian-born German mathematician Georg Cantor (1845–1918) between 1874 and 1897 to deal with collections of objects, called sets (1). A set is usually represented by an upper-case letter or by a pair of curly brackets enclosing all of its members; thus the set of all additive primary colours is the set *C* = {red, green, blue}; the set of natural numbers is *N* = {1, 2, 3, … }; and the set of female US presidents is *F* = Ø, which is called the *empty set* or *null set*. See also barber paradox, Boolean, fuzzy set, Russell's paradox.

**From:**
set theory
in
A Dictionary of Psychology »

*Subjects:*
Philosophy — Psychology.