The vector operator nabla

If the scalar S and the components of the vectors A, B,C,D commute with one another, the following relations are satisfied 

The following relations involving the position vector r(x, y, z) hold true 

The relations involving the reciprocal distance are more complex 

Instead of the infinity symbol it is more appropriate to speak about a singular function. However, the operator V2(l/r) occurs in integrals of the form 

This is the definition of the Dirac function which is zero everywhere except at x = 0. It is infinite in such a way that the area under it is unity 

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