http://farside.ph.utexas.edu/teaching/qm/lectures/node53.html(adsbygoogle = window.adsbygoogle || []).push({});

So I was reading this and I don't understand how he goes from 658 to 661 using the completeness relation. In 661 if you use the completeness relaton can you get rid of the I n,l''>s by doing the outer product and ignoring the inner product first? I mean if you get rid of I n,l''>s you get <n,l'I H_1 In,l1>which equals lamba etc.

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# Degenerate Perturbation Theory

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