Let Γ be a finitely generated, amenable group. Using an idea of É Ghys, we prove that if Γ has a nontrivial, orientation-preserving action on the real line, then Γ has an infinite, cyclic quotient. (The converse is obvious.) This implies that if Γ has a faithful action on the circle, then some finite-index subgroup of Γ has the property that all of its nontrivial, finitely generated subgroups have infinite, cyclic quotients. It also means that every left-orderable, amenable group is locally indicable. This answers a question of P Linnell.
Morris, Dave Witte  1
@article{10_2140_agt_2006_6_2509,
author = {Morris, Dave Witte},
title = {Amenable groups that act on the line},
journal = {Algebraic and Geometric Topology},
pages = {2509--2518},
year = {2006},
volume = {6},
number = {5},
doi = {10.2140/agt.2006.6.2509},
url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2006.6.2509/}
}
Morris, Dave Witte. Amenable groups that act on the line. Algebraic and Geometric Topology, Tome 6 (2006) no. 5, pp. 2509-2518. doi: 10.2140/agt.2006.6.2509
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