List of Symbols Natural or counting numbers: = {1, 2, 3, 4, 5, ...} Prime numbers = {2, 3, 5, 7, 11, 13, ...} Whole numbers = W = {0, 1, 2, 3, 4, 5, ...} Integer numbers = = {..., -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, ...} Rational numbers = = {numbers of the form a/b with a and b integers and b 0} Irrational numbers = {numbers that cannot be represented as the quotient of two integers} Real numbers = = {all rational and irrational numbers} Complex numbers = = {numbers of the form a+ib with a and b real numbers and i such that i 2 = -1} n! = n × ðn - 1Þ × ðn - 2Þ × ... × 3 × 2 × 1 n! (read "n factorial") is defined for all n 0. By definition 0! =1. {x | x has a certain property} gives the description of a set. In this context the symbol "|" is read "such that." All objects that have the required property are called "elements" of the set. a A: a is an element of the set A (see Section on Basic Set Theory in Chapter 4) a A: a is not an element of the set A (see Section on Basic Set Theory in Chapter 4) A B: the set A is contained (or equal to) in the set B (see Section on Basic Set Theory in Chapter 4) A B: read "A union B" (see Section on Basic Set Theory in Chapter 4) A B: read "A intersection B" (see Section on Basic Set Theory in Chapter 4) A' = C(A): read "complement of A" (see Section & Basic Set Theory in Chapter 4) on x when x 0 |x| = absolute value of x = distance from 0 to x = - x when x < 0