# Introducing expressions

Variables are not the only things in Puppet that have a value. Expressions also have a value. The simplest expressions are just literal values:

```42
true
'Oh no, not again.'```

You can combine numeric values with arithmetic operators, such as `+`, `-`, `*`, and `/`, to create arithmetic expressions, which have a numeric value, and you can use these to have Puppet do calculations (`expression_numeric.pp`):

```\$value = (17 * 8) + (12 / 4) - 1
notice(\$value)```

The most useful expressions, though, are those which evaluate to `true` or `false`, known as Boolean expressions. The following is a set of examples of Boolean expressions, all of which evaluate to `true` (`expression_boolean.pp`):

`notice(9 < 10) notice(11 > 10) notice(10 >= 10) notice(10 <= 10) notice('foo' ...`

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