Can someone please tell me what the integrand in the below equation mean?(adsbygoogle = window.adsbygoogle || []).push({});

[tex] 1 = \langle \psi | \psi \rangle = \int_{-\infty}^{\infty} d \langle \psi |E_\lambda \psi \rangle [/tex]

where,

[tex]E_\lambda[/tex] is an increasing (and absolutely continuous) function of projection operators such that [tex]\int_{-\infty}^{\infty} dE_\lambda = I [/tex]

( I read the integrand as a differential (or measure) of a complex constant, which should have been zero!? So I am certainly wrong in interpreting it)

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# Spectral theory in quantum mechanics

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