# 9.59 OrderedVariableListΒΆ

The domain OrderedVariableList provides symbols which are restricted to a particular list and have a definite ordering. Those two features are specified by a List Symbol object that is the argument to the domain.

This is a sample ordering of three symbols.

```
ls:List Symbol:=['x,'a,'z]
```

\[\]

[x,a,z] |

_{Type: List Symbol}

Let’s build the domain

```
Z:=OVAR ls
```

\[\]

OrderedVariableList[x,a,z] |

_{Type: Domain}

How many variables does it have?

```
size()$Z
```

\[\]

3 |

_{Type: NonNegativeInteger}

They are (in the imposed order)

```
lv:=[index(i::PI)$Z for i in 1..size()$Z]
```

\[\]

[x,a,z] |

_{Type: List OrderedVariableList [x,a,z]}

Check that the ordering is right

```
sorted?(>,lv)
```

\[\]

true |

_{Type: Boolean}