So, if B | ψ ψ n ⟩ ⟩ ≠ ≠ 0 , we can say that B | ψ ψ n ⟩ ⟩ is an eigenket of A corresponding to the eigenvalue a n . Since both B | ψ ψ n ⟩ ⟩ and | ψ ψ n ⟩ ⟩ are eigenkets associated with the same non-degenerate eigenvalue a n , they can differ at most by a multiplicative constant. We call this constant b n . So,