set theory

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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.

Subjects: Philosophy — Psychology.

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