ABSTRACT
In this chapter we develop a little of the theory of sets. Most of the material israther easy, and much of it is devoted to various definitions and notations to beused in future chapters.
We begin with a couple of definitions. DEFINITION Let A and B be sets. The union of A and B, writtenA∪B, is the set consisting of all elements that lie in either A or B (or
both). Symbolically,
A∪B = {x |x ∈ A or x ∈ B} . The intersection of A and B, written A∩B, is the set consisting of all elements that lie in both A and B; thus
A∩B = {x |x ∈ A and x ∈ B} . Example 17.1
(1) If A = {1,2,3} and B = {2,4}, then A∪B = {1,2,3,4} and A∩B = {2}.
