### 2.37.10 Modify an element in a list : `subsop`

`subsop` modifies an element in a list. `subsop` takes as argument a list and an equality (an index=a new value) in all syntax modes, but in `Maple` syntax mode the order of the arguments is reversed.
Remark If the second argument is `’k=NULL’`, the element of index `k` is removed of the list.
Input in `Xcas` mode (the index of the first element is 0) :

`subsop([0,1,2],1=5)`

Or :

`L:=[0,1,2];L[1]:=5`

Output :

`[0,5,2]`

Input in `Xcas` mode (the index of the first element is 0) :

`subsop([0,1,2],’1=NULL’)`

Output :

`[0,2]`

Input in `Mupad TI` mode (the index of the first element is 1) :

`subsop([0,1,2],2=5)`

Or :

`L:=[0,1,2];L[2]:=5`

Output :

`[0,5,2]`

In `Maple` mode the arguments are permuted and the index of the first element is 1.
Input :

`subsop(2=5,[0,1,2])`

Or :

`L:=[0,1,2];L[2]:=5`

Output :

`[0,5,2]`