In his Comment, Elsasser claims that the answer to my titular question is one, not four as I have it. He goes on to give the singular principle that supposedly captures the difference between a light-bulb and a laser: $g^{(2)}(tau=0)=1$. His claim is unconsidered and wrong, his proposed principle is impossible to apply and, when corrected, redundant (it then becomes one of the four I list already), his arguments are manifestly misdirected. My paper stands as is.
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