# Defining Expression elements

Expression elements allow you to combine other network elements with logical operators to represent complex sets of IP addresses.

Figure: Expression element properties

1
  Click Add Element to select an element to use in the Expression.
2
  Logical operators
3
  Undo and redo actions
4
  The Expression

Logical Operators in Expressions are resolved in the following order (however, items inside parentheses are evaluated before any items outside parentheses are considered):

1. Negations
2. Intersections
3. Unions

## Expression Properties dialog box

Use this dialog box to create expressions. Expression elements combine other network elements (IP addresses) with logical operands.

Option | Definition
--- | ---
Name | The name of the element.
Comment (Optional) | A comment for your own reference.
Category (Optional) | Includes the element in predefined categories. Click Select to select a category.

Option | Definition
--- | ---
Expression Composer
Add Element | Select this option to select the elements to use in the Expression.
Union | Includes all IP addresses defined in both elements that the union combines.
Intersection | Includes only those IP addresses that the two elements that the intersection combines have in common.
Negation | Includes all IP addresses except those that are defined in the element that follows the negation.
Open Parenthesis | Parentheses group parts of the expression together. Items inside parenthesis are evaluated before they are compared to items outside the parenthesis.
Close Parenthesis | Parentheses group parts of the expression together. Items inside parenthesis are evaluated before they are compared to items outside the parenthesis.
Undo | Click to undo the last action you did.
Redo | Click to redo the last action you did.