SETS

A mathematical set must be defined either by a list, a rule or a formula, so that its elements can be recognized without any doubt or ambiguity. If N is a set, we write n E N meaning that 'n is a member of the set N'. The set of all elements that are being considered in a problem is called the reference set (or universal set), and it is denoted by E or U. The empty set has no elements (compare it with the empty drawer of a desk); it is denoted by O. Any collection of elements of E, ranging from O to E it self, is called a subset of E.