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Let $S$ be a closed oriented surface and $C(S, n)$ be the configuration space of $n$ points on $S$, i.e., the space of $n$-tuples of distinct points of $S$ with the topology induced from $S^n$. Let $V \subset S$ be a set of $n$ distinct points. Let ${\rm Homeo}_0(S)$ be the topological group (with compact-open topology) of homeomorphisms $S \rightarrow S$ isotopic to identity, and ${\rm Homeo}_0(S, V)$ be the subgroup of those that fix $V$ and can be isotopic to identity by an isotopy fixing $V$. Denote by $H(S, V)$ the topological space obtained in the quotient of ${\rm Homeo}_0(S)$ by ${\rm Homeo}_0(S, V)$.

Every homeomorphism $h: S \rightarrow S$ extends to a homeomorphism $h_n: C(S, n) \rightarrow C(S, n)$, and eventually to a homeomorphism $\tilde h_n: \widetilde{C(S, n)} \rightarrow \widetilde{C(S, n)}$ of the universal cover of $C(S, n)$. By fixing an arbitrary lift $\tilde V \in \widetilde{C(S, n)}$ of $V$ and noting that the extensions of homeomorphisms in ${\rm Homeo}_0(S, V)$ fix $\tilde V$ we get a continuous map from $H(S, V)$ to $\widetilde{C(S, n)}$. I think, a can prove that it is a homeomorphism, but I'm not very comfortable with my proof, and think that this can be known. Does anyone know a reference for this?

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  • $\begingroup$ doesn't this follow shortly enough from the isomorphism between braid groups and mapping class groups? $\endgroup$
    – alesia
    Commented Nov 16, 2023 at 22:27
  • $\begingroup$ There is an "evaluation at $V$" map from $\mathrm{Homeo}_0(S)$ to $C(S,n)$, which I believe is a fibration with fibre $\mathrm{Homeo}_0(S,V)$. Does this imply that the quotient is in fact $C(S,n)$? $\endgroup$
    – Mark Grant
    Commented Nov 17, 2023 at 7:06
  • $\begingroup$ @alesia, I'd love to see such an argument, but unfortunately, I couldn't so far produce it myself. Please note that all the homeomorphisms in question are supposed to be isotopic to identity on $S$. $\endgroup$
    – Roman
    Commented Nov 17, 2023 at 11:49
  • $\begingroup$ @MarkGrant, Yes, the evaluation map ${\rm Homeo_0}(S)/{\rm Homeo_0}(S, V) \rightarrow C(S, n)$ is a homeomorphism. The subtlest part is the openness of this map. The standard proof of the openness seems also to extend to the openness of the map in my question. I think, I can then to do an inductive argument to show that my map is a bijection, but it is a bit annoying. I wonder if nobody came to this before, or if there is a simpler proof. $\endgroup$
    – Roman
    Commented Nov 17, 2023 at 11:53

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