Let w 1 , … , w n {\displaystyle {}w_{1},\ldots ,w_{n}} be a basis of W {\displaystyle {}W} and w 1 ∗ , … , w n ∗ {\displaystyle {}w_{1}^{*},\ldots ,w_{n}^{*}} the corresponding dual basis. We set
Then, for every vector v ∈ V {\displaystyle {}v\in V} , we have
where the last equation rests on fact.