... electrons¹

According to the antisymmetry principle for fermions, of which the Pauli principle  is a direct result.

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... way.²

Some texts talk about the ``average'' electron repulsion term in the Fock operator; I find this misleading in that Hartree-Fock uses the same instantaneous interelectron repulsion term as CI--it's the same Hamiltonian! The restriction to a single Slater determinant is what causes the averaging of interelectron repulsions.

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... expect!³

However, state-of-the-art determinant-based CI algorithms often include computational simplifications if the M_s = 0 component is used [16].

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...).⁴

Reference [28] contains a minor mistake, giving (pq|rs) as $\langle pq \vert rs \rangle$.

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... spin-orbitals.⁵

In the determinant CI expansion, we restrict all determinants to a single value of M_s.

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...+1.⁶

This differs somewhat from Duch [27], who sometimes uses ${\bar Y}(e, o)$ to denote the arc entering vertex (e, o) in reverse-lexical addressing.

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