University of California, San Diego: Edward Bender and S. Williamson's "Sets, Equivalence and Order: Sets and Functions"
This time, focus on complement of a set. Complement is set difference with respect to the largest set, called the universal set, namely, E - A is the complement of A. E is the universal set, the set of all elements; when sets are defined, the type of the elements is specified. For example, in a set of all red cars, the type of the members in this example, is car. We also say that the domain of the elements is the (universal) set of all cars.