Title: Moduli Spaces of Unordered $n\ge5$ Points on the Riemann Sphere and Their Singularities,
Abstract: For $n\ge5$, it is well known that the moduli space $\mathfrak{M_{0,\:n}}$ of
unordered $n$ points on the Riemann sphere is a quotient space of the Zariski
open set $K_n$ of $\mathbb C^{n-3}$ by an $S_n$ action. The stabilizers of this
$S_n$ action at certain points of this Zariski open set $K_n$ correspond to the
groups fixing the sets of $n$ points on the Riemann sphere. Let $\alpha$ be a
subset of $n$ distinct points on the Riemann sphere. We call the group of all
linear fractional transformations leaving $\alpha$ invariant the stabilizer of
$\alpha$, which is finite by observation. For each non-trivial finite subgroup
$G$ of the group ${\rm PSL}(2,{\Bbb C})$ of linear fractional transformations,
we give the necessary and sufficient condition for finite subsets of the
Riemann sphere under which the stabilizers of them are conjugate to $G$. We
also prove that there does exist some finite subset of the Riemann sphere whose
stabilizer coincides with $G$. Next we obtain the irreducible decompositions of
the representations of the stabilizers on the tangent spaces at the
singularities of $\mathfrak{M_{0,\:n}}$. At last, on $\mathfrak{M_{0,\:5}}$ and
$\mathfrak{M_{0,\:6}}$, we work out explicitly the singularities and the
representations of their stabilizers on the tangent spaces at them.