Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In set theory, the union (denoted as ) of a collection of sets is the set of all distinct elements in the collection. The union of a collection of sets S_1, S_2, S_3, dots , S_n,! gives a set S_1 cup S_2 cup S_3 cup dots cup S_n.Other more complex operations can be done including the union, if the set is for example defined by a property rather than a finite or assumed infinite enumeration of elements. As an example, a set could be defined by a property or algebraic equation, which is referred to as a solution set when resolved.If we are then to refer to a single element by the variable "x", then we can say that x is a member of the union if it is an element present in set A or in set B, or both.