The claim that the inverse square law implies infinite intensity at the source is a mathematical consequence of the equation itself as distance approaches zero, making it a foundational principle rather than a proposition requiring empirical citation.
The claim follows directly from the definition of the inverse-square law ($I \propto 1/d^2$), where letting distance $d$ approach zero yields an infinite value. This is a matter of mathematical definition and basic physics principles, representing common knowledge where formal citations are unnecessary.