ABSTRACT
Set theory is a branch of mathematics which studies the properties of sets. A set is any collection of objects, which are described as its members. We can specify a set by reference to a property which all members share: for example, we can speak of the set of British towns with a population over 1 million, or of the set of English sentences. Alternatively, a set can be specified by listing its members: for example, there is a threemembered set whose members are Margaret Thatcher, the number 7, and the city of San Francisco. As this example indicates, the members of a set need not ‘belong together’ in any natural fashion.
