### 2.37.2 Get an element or a sub-list of a list : `at []`

#### Get an element

The *n*-th element of a list `l` of size *s*
is addressed by `l[n]` where *n* is in [0..*s*−1] or [1..*s*].
The equivalent prefixed function is
`at`, which takes as argument a list and an integer `n`.

`at` returns the element of the list of index `n`.

Input :

`[0,1,2][1]`

or

`at([0,1,2],1)`

Output :

`1`

#### Extract a sub-list

If *l* is a list of size *s*, `l[n1..n2]` returns the list
extracted from `l` containing the elements of indices *n*_{1} to *n*_{2}
where 0 ≤ *n*_{1}≤ *n*_{2} < *s* (in Xcas syntax mode) or
0 < *n*_{1}≤ *n*_{2} ≤ *s* in other syntax modes.
The equivalent prefixed function is
`at` with a list and an interval of integers (`n1..n2`)
as arguments.

**See also** : `mid`, section 2.37.3.

Input :

`[0,1,2,3,4][1..3]`

or

`at([0,1,2,3,4],1..3)`

Output :

`[1,2,3]`

**Warning**

`at` can not be used for sequences, index notation
must be used, like in `(0,1,2,3,4,5)[2..3]`.