Kernel of a linear application : kernel nullspace ker

### 2.43.12 Kernel of a linear application : `kernel nullspace ker`

`ker` (or `kernel` or `nullspace`) takes as argument the matrix of an linear application f with respect to the canonical basis.
`ker` (or `kernel` or `nullspace`) returns a list of vectors that is a basis of the kernel of f.
Input :

`ker([[1,1,2],[2,1,3],[3,1,4]])`

Output :

`[[1,1,-1]]`

The kernel is generated by the vector `[1,1,-1]`.