Graphically, Slater-Determinants may be represented by MO or SO diagrams. With {•, ↑, ↓} representing an occupied MO/SO orbital, while a vacancy represents an unfilled virtual orbital, an example is shown in fig. . For Unrestricted (U) states, the energies need-not be equal between the two different spins (center-right). If we have no restriction on spin, and desire to include spin-flip situations the Generalized (G) theory is given by the right diagram.