# Introduction to expressions

An expression is an element that combines other network elements (IP addresses) with logical operands.

Expressions make it easier to define complex sets of network resources, even though you can arrive at the same definitions without expressions. For example, a single, simple expression can include a whole network except for a few individual IP addresses scattered throughout the address space. Otherwise, several Address Range elements might be needed for defining the same set of IP addresses.

The expressions consist of the following parts:

- Parentheses group sets of elements and define the processing order in the same way as they do in mathematical equations. The parentheses in expressions are always the basic curved type “(” and “)”.
- Negation operators take a set and form a new set that includes every possible element except the ones in the original set. Negations are expressed with “~”.
- Intersection operators take two sets and forms a new set that includes only those IP addresses that are found in both sets. Intersections are expressed with “⋂”.
- Union operators combine two sets and form a new set that includes every IP address in both sets. Unions are expressed with “⋃”.