// Create a `OrbitalIntegral` instance to store a two-electron molecular
    // orbital integral data.
    var twoElectronIntegral = new OrbitalIntegral(new[] { 0, 1, 2, 3 }, 0.123);

    // This enumerates all spin-orbital indices of the `FermionTerm`s in the 
    // Hamiltonian represented by this integral -- this is an array of array 
    // of `SpinOrbital` instances.
    var twoElectronSpinOrbitalIndices = twoElectronIntegral.EnumerateSpinOrbitals();