These values are called the quantum numbers of the state.
Classical quantities are continuous real-valued functions on .
Bohr and Sommerfeld assumed that nature really permits only a subset to occur as stationary states. They assumed further, for certain classical , that the image was a discrete subset of R . Quantum states are specified by elements of the space. If a Hermitian operator has a discrete spectrum, and is an eigenvector of with eigenvalue , then we say that is a quantum number of the state specified by . Consider first the hydrogen atom.