A peculiarity of this construction is in the fact that there exists the operator A = ( n ^ ^ ⋅ ⋅ J → → ) 2 which commutes both with the Hamiltonian and with J → → 2 , J z . Then the states are labeled also by the eigenvalue a of the operator A : ψ ψ = ψ ψ l m a ( k → → , n ^ ^ ) . For given angular momentum l , there are l + 1 such the states. All of them are degenerate, i.e. belong to the same mass (if we do not make an approximation). However, the wave function should also satisfy the so-called angular condition After satisfying it, the solution obtains the form of a unique superposition of the states ψ ψ l m a ( k → → , n ^ ^ ) with different eigenvalues a .