That can be done by a chaining contextual substitution. This is probably the most compact way to write that, but may be difficult to understand for a beginner:

in a `calt`

feature:

```
sub @numbers' lookup Left @numbers' lookup Middle @numbers' lookup Right;
```

and a prefix containing some lookups:

```
@numbers = [one two three four five six seven eight nine zero];
lookup Left {
sub @numbers by [one.left two.left three.left four.left five.left six.left seven.left eight.left nine.left zero.left];
} ALeft;
lookup Middle {
sub @numbers by [one.middle two.middle three.middle four.middle five.middle six.middle seven.middle eight.middle nine.middle zero.middle];
} AMiddle;
lookup Right {
sub @numbers by [one.right two.right three.right four.right five.right six.right seven.right eight.right nine.right zero.right];
} ARight;
```