The space of immersed polygons

Abstract

We use the Schwarz-Christoffel formula to show that for every $n\geq 3$, the space of labelled immersed $n$-gons in the plane up to similarity is homeomorphic to $\mathbb{R}^{2n-4}$. We then prove that all immersed triangles, quadrilaterals, and pentagons are embedded, from which it follows that the space of labelled simple $n$-gons up to similarity is homeomorphic to $\mathbb{R}^{2n-4}$ if $n\in \{3,4,5\}$. This was first shown by Gonz\'ales and L\'opez-L\'opez for $n=4$ and conjectured to be true for every $n\geq 5$ by Gonz\'alez and Sedano-Mendoza.