Imagine there is a molecule which consists of several atoms, and for each atom there is an effective orbital, phi_i, which are not orthogonal. Now we want to construct from them a set of orthogonal orbitals, psi_i. Of course there are many ways to do this. Let W be the matrix that realizes our requirement, i.e., \sum_jW_{ij}phi_j=psi_i. The question is, can one assert that, it is always possible to get a W whose off-diagonal elements are unanimously much smaller that its diagonal ones?