is it correct that the following integral is, actually, a triple integral of the variable $r$? (it has to do with electromagnetic calculations) The integral is symbolised with a single S integration symbol (integration to "everywhere" -meaning- to all the area the charge extends- then comes the function $f(r)$ where $r\ge 0$ and the integrity element is not dr but $d^3r$. Note that the $f(r)$ function is actually a product of two functions which are both able to be integrated seperatedly, and are continuous functions.
$$\int_D f(r) \, d^3r,\qquad r>0$$
The above are referring to Green's theorem. Thank you.