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 $\leq$ n₁ $\leq$ n₂ < s (in Xcas syntax mode) or 0 < n₁ $\leq$ n₂ $\leq$ 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 1.37.3.
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].