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

### 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 n1 to n2 where 0 ≤ n1≤ n2 < s (in Xcas syntax mode) or 0 < n1≤ n2 ≤ 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]`.