These can be additionally labeled with a subscript giving m. There are 2 n states with principal quantum number n, 4 j +2 of them with any allowed j except the highest (j = n −1/2) for which there are only 2 j +1. Since the orbitals having given values of n and j have the same energy according to the Dirac equation, they form a basis for the space of functions having that energy.