### 2.43.9 Basis of a linear subspace : `basis`

`basis` takes as argument a list of vectors generating
a linear subspace of ℝ^{n}.

`basis` returns a list of vectors, that is a basis of this
linear subspace.

Input :

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

Output :

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