Let us have an operator A ^ ^ of an observable A , which has all non-degenerate eigenvalues { a n } . As a result, there is one unique eigenstate corresponding to each eigenvalue, allowing us to label these by their respective eigenvalues. For example, the eigenstate of A ^ ^ corresponding to the eigenvalue a n can be labelled as | a n ⟩ ⟩ . Such an observable is itself a self-sufficient CSCO.