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a well-defined collection of objects; that is, it is defined in such a manner that we can determine for any given object x x x whether or not x x x belongs to the set. The objects that belong to a set are called its elements or members . We will denote sets by capital letters, such as A A A or X ; X ; X\text{;} if a a a is an element of the set A , A , A\text{,} we write

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