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A *boolean expression* is a combination of relational or
matching expressions using the boolean operators `and`

, `or`

and `not`

, and, eventually, parentheses to control nesting:

Expression | Result |
---|---|

x `and` y | True only if both x and
y are true. |

x `or` y | True if any of x or y
is true. |

`not` x | True if x is false. |

Binary boolean expressions are computed using *shortcut evaluation*:

`x`and`y`If

, the result is`x`⇒`false`

`false`

and`y`is not evaluated.`x`or`y`If

, the result is`x`⇒`true`

`true`

and`y`is not evaluated.