Homeotopy groups of leaf spaces of one-dimensional foliations on non-compact surfaces with non-compact leaves

TL;DR

This paper studies the homeotopy groups of leaf spaces of one-dimensional foliations on non-compact surfaces, revealing a duality with automorphisms of a graph encoding the surface's gluing structure.

Contribution

It establishes a homomorphism between the homeotopy group of leaf-preserving homeomorphisms and that of the leaf space, showing the map is either injective or has kernel Z_2, thus providing a dual description.

Findings

The homomorphism between homeotopy groups is either injective or has kernel Z_2.

The duality links the homeotopy group to automorphisms of a graph encoding the surface's structure.

Provides a new perspective on the topology of leaf spaces via combinatorial graph automorphisms.

Abstract

Let $Z$ be a non-compact two-dimensional manifold obtained from a family of open strips $\mathbb{R}\times(0,1)$ with boundary intervals by gluing those strips along some pairs of their boundary intervals. Every such strip has a natural foliation into parallel lines $\mathbb{R}\times t$, $t\in(0,1)$, and boundary intervals which gives a foliation $\Delta$ on all of $Z$. Denote by $\mathcal{H}(Z,\Delta)$ the group of all homeomorphisms of $Z$ that maps leaves of $\Delta$ onto leaves and by $\mathcal{H}(Z/\Delta)$ the group of homeomorphisms of the space of leaves endowed with the corresponding compact open topologies. Recently, the authors identified the homeotopy group $\pi_0\mathcal{H}(Z,\Delta)$ with a group of automorphisms of a certain graph $G$ with the additional structure which encodes the combinatorics of gluing $Z$ from strips. That graph is in a certain sense dual to the space of leaves $Z/\Delta$. On the other hand, for every $h\in\mathcal{H}(Z,\Delta)$ the induced permutation $k$ of leaves of $\Delta$ is in fact a homeomorphism of $Z/\Delta$ and the correspondence $h\mapsto k$ is a homomorphism $\psi:\mathcal{H}(\Delta)\to\mathcal{H}(Z/\Delta)$. The aim of the present paper is to show that $\psi$ induces a homomorphism of the corresponding homeotopy groups $\psi_0:\pi_0\mathcal{H}(Z,\Delta)\to\pi_0\mathcal{H}(Z/\Delta)$ which turns out to be either injective or having a kernel $\mathbb{Z}_2$. This gives a dual description of $\pi_0\mathcal{H}(Z,\Delta)$ in terms of the space of leaves.