set (redirected from set up)

Set, in Egyptian religion

Set or Seth (both: sĕt or sāt), in Egyptian religion, god of evil. Set was a sun god of predynastic Egypt, but he gradually degenerated from being a beneficent deity into being a god of evil and darkness. In a widespread Egyptian myth he murdered his brother Osiris and was in turn defeated by Horus, the son of Osiris. The Greeks identified Set with Typhon.

---

set, in mathematics

set, in mathematics, collection of entities, called elements of the set, that may be real objects or conceptual entities. Set theory not only is involved in many areas of mathematics but has important applications in other fields as well, e.g., computer technology and atomic and nuclear physics.

Definition of Sets

A set must be well defined; i.e., for any given object, it must be unambiguous whether or not the object is an element of the set. For example, if a set contains all the chairs in a designated room, then any chair can be determined either to be in or not in the set. If there were no chairs in the room, the set would be called the empty, or null, set, i.e., one containing no elements. A set is usually designated by a capital letter. If A is the set of even numbers between 1 and 9, then A={2, 4, 6, 8}. The braces, {}, are commonly used to enclose the listed elements of a set. The elements of a set may be described without actually being listed. If B is the set of real numbers that are solutions of the equation x²=9, then the set can be written as B={x:x²=9} or B={x|x²=9}, both of which are read: B is the set of all x such that x²=9; hence B is the set {3,−3}.

Membership in a set is indicated by the symbol ∈ and nonmembership by ∉; thus, x∈A means that element x is a member of the set A (read simply as "x is a member of A") and y∉A means y is not a member of A. The symbols ⊂ and ⊃ are used to indicate that one set A is contained within or contains another set B; A⊂B means that A is contained within, or is a subset of, B; and A⊃B means that A contains, or is a superset of, B.

Operations on Sets

There are three basic set operations: intersection, union, and complementation. The intersection of two sets is the set containing the elements common to the two sets and is denoted by the symbol ∩. The union of two sets is the set containing all elements belonging to either one of the sets or to both, denoted by the symbol ∪. Thus, if C={1, 2, 3, 4} and D={3, 4, 5}, then C∩D={3, 4} and C∪D={1, 2, 3, 4, 5}. These two operations each obey the associative law and the commutative law, and together they obey the distributive law.

In any discussion the set of all elements under consideration must be specified, and it is called the universal set. If the universal set is U={1, 2, 3, 4, 5} and A={1, 2, 3}, then the complement of A (written A′) is the set of all elements in the universal set that are not in A, or A′={4, 5}. The intersection of a set and its complement is the empty set (denoted by ∅), or A∩A′=∅; the union of a set and its complement is the universal set, or A∪A′=U. See also symbolic logic.

---

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, {2x | x = 1,2,3,...} represents the set of positive even numbers (the vertical bar means “such that”).

---

(Secure Electronic Transaction) A standard protocol from MasterCard and Visa for securing online credit card payments via the Internet. It is a three-way transaction: the user, merchant and bank must use the SET protocols.

Credit card data and a digital certificate (for authentication) is stored in a plug-in to the user's Web browser. The order is received by a SET-enabled merchant server that passes encrypted payment information to the bank. Approval is electronically sent to the merchant.

---

1.	(security)	SET - Secure Electronic Transaction.
2.	(electronics)	SET - Single Electron Tunneling.
3.	(standard)	SET - Standard d'Echange et de Transfert.
4.		set - A collection of objects, known as the elements of the set, specified in such a way that we can tell in principle whether or not a given object belongs to it. E.g. the set of all prime numbers, the set of zeros of the cosine function. For each set there is a predicate (or property) which is true for (possessed by) exactly those objects which are elements of the set. The predicate may be defined by the set or vice versa. Order and repetition of elements within the set are irrelevant so, for example, 1, 2, 3 = 3, 2, 1 = 1, 3, 1, 2, 2. Some common set of numbers are given the following names: N = the natural numbers 0, 1, 2, ... Z = the integers ..., -2, -1, 0, 1, 2, ... Q = the rational numbers p/q where p, q are in Z and q /= 0. R = the real numbers C = the complex numbers. The empty set is the set with no elements. The intersection of two sets X and Y is the set containing all the elements x such that x is in X and x is in Y. The union of two sets is the set containing all the elements x such that x is in X or x is in Y. See also set complement.