Set

In mathematics and logic, any collection of objects (elements), which may be mathematical (e.g., numbers, functions) or not. The intuitive idea of a set is probably even older than that of number. Members of a herd of animals, for example, could be matched with stones in a sack without members of either set actually being counted. The notion extends into the infinite.

For example, the set of integers from 1 to 100 is finite, whereas the set of all integers is infinite. A set is commonly represented as a list of all its members enclosed in braces. A set with no members is called an empty, or null, set, and is denoted ∅. Because an infinite set cannot be listed, it is usually represented by a formula that generates its elements when applied to the elements of the set of counting numbers. Thus, {2&math.x; | &math.x; = 1,2,3,...} represents the set of positive even numbers (the vertical bar means “such that”).