As guaranteed by Rosina's theorem, there exists a bijection from the exact wavefunction to 2 Γ of a non-degenerate ground state. Therefore, for a system with 2-body terms and fewer in the Hamiltonian, the 2-RDM contains the information required to obtain all higher-order RDMs and the exact wavefunction. This property is not true of the 1-RDM nor the electron density despite both being able to yield the exact energies, in principle. A recent extension of the theorem is also valid for degenerate states differentiable by a two-particle operator. These features have made 2-RDM-based methodologies very compelling, especially with regard to strong correlation. Seminal works by Yang and Coleman investigating the properties of the p-RDMs of fermionic systems have also demonstrated that large eigenvalues of the 2-RDM are connected to "off-diagonal long range order" (ODLRO) , which has been associated with phenomena such as superconductivity due to electronic degrees of freedom and exciton condensation, while diagonal long range order (DLRO) makes an appearance in magnetism. In analogy with the 1-RDM and the natural orbitals, the eigenvectors of the 2-RDM correspond to the natural geminals of the system.