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isn't it a bit dangerous to claim that

[tex]\left[ x \cdot \left( \psi(x,t) \, \frac{\partial \psi^\ast (x,t)}{\partial x} + \psi^\ast(x,t) \, \frac{\partial \psi(x,t)}{\partial x} \right) \right]_{x=-\infty}^{x=\infty} = 0[/tex]

for example?

Expressions like this one are often found in popular quantum mechanics textbooks. How do you justify such expressions? I would prefer a mathematical- instead of a physical explanation...

With best regards

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# Justification of a common calculation

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