### 5.46.9 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]]