= Galaxy two-point correlation function
{title2=$dP_{12}=\bar n^2[1+\xi(r)]dV_1dV_2$}
For a homogeneous isotropic <point process> of <galaxies> with mean number density $\bar n$, the <galaxy two-point correlation function> gives the excess pair probability at distinct positions. Dividing the factorial pair density by the probability of a central <galaxy> gives conditional neighbouring-galaxy density $\bar n[1+\xi(r)]$. Choosing a central location uniformly in volume does not perform this conditioning.
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