# Edit Expression elements

The criteria in an expression combine network elements (IP addresses) with logical operators.

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For more details about the product and how to configure features, click Help or press F1.

## Steps

1. Select Configuration, then browse to Network Elements.
2. Browse to Expressions.
3. Right-click an Expression element, then select Properties.
4. Click inside the expression to display the cursor.
   You can move the cursor using the arrow keys on your keyboard.
5. Click Add Element to add a new element, or click a logical operator.
   Expressions can start with a negation operation or a section in parentheses.
6. To delete an element or logical operator, use the Delete or Backspace key on your keyboard.
7. Click OK to save your changes.

## Examples

- Expression that selects any network other than one internal network (172.16.1.0/24):
- Expression for selecting Hosts in the Network 172.16.1.0/24 from a Group element that contains Hosts from many different networks:

## 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.