Atomic orbitals reductive view

Note that (2.19) is a manifestly hermitian form of the orbit-orbit interaction familiar from atomic physics, usually described in texts as resulting from the reduction of the Breit operator (2.8) to n.r. form. This is unfortunate from a pedagogical point of view, since the Breit operator refers only to spin-1/2 particles. Spin has nothing to do with it I will return to the difference between (2.18) and (2.19) shortly. 

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