  In his Comment, Els\"asser 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.
