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# 4: Sets

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• 4.1: An Introduction to Sets
A set is a collection of objects. The objects in a set are called its elements or members. The elements in a set can be any types of objects, including sets! The members of a set do not even have to be of the same type. For example, although it may not have any meaningful application, a set can consist of numbers and names.
• 4.2: Subsets and Power Sets
We usually consider sets containing elements of similar types. The collection of all the objects under consideration is called the universal set, and is denoted U.
• 4.3: Unions and Intersections
We can form a new set from existing sets by carrying out a set operation.
• 4.4: Cartesian Products
• 4.5: Index Sets