So I saw this a moment ago:(adsbygoogle = window.adsbygoogle || []).push({});

How can the second and third terms yield (n+1)+(n-1)=2n and not (n+1)+n=2n+1?

PS: I solved the problem by using [a,a(+)]=1.

Sorry, this is very simple but I cannot figure out what I did wrong.

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# Calculating a matrix element & first order shift

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