
The universal covering group \(\widetilde{\hbox{Homeo}}_ +(S^ 1)\) of \(\hbox{Homeo}_ +(S^ 1)\) is the subgroup of \(\hbox{Homeo}_ +(\mathbb{R})\) consisting of all \(\tilde f\) that commute with translation by 1. A theorem of Eisenbud, Hirsch, and Neumann asserts that \(\tilde f\in \widetilde{\hbox{Homeo}}_ +(S^ 1)\) is a product of \(k\) commutators if and only if \(\overline m(\tilde f)1- 2k\), \(\overline m(\tilde f)\) and \(\underline{m}(\tilde f)\) being the maximum and minimum values, respectively, of \(f(x)-x\) on \(\mathbb{R}\). The author shows that the \(PL\) version of this theorem fails. He also proves that translation \(T_ a: \mathbb{R}\to\mathbb{R}\) by \(a\in\mathbb{R}\) is a product of \(k\geq 1\) commutators in \(\widetilde {PL}_ +(S^ 1)\) if and only if \(| a|<2k-1\). This is applied to obtain the piecewise linear version of a theorem of Milnor and Wood: An oriented, \(C^ 0\) circle bundle \(E\) over a closed, oriented surface \(\Sigma\) of genus \(\geq 1\) admits a transversely \(PL\) foliation transverse to the fibers if and only if \(| \text{eu}(E)|\leq |\chi(\Sigma)|\).
transversely \(PL\) foliation, Topology of vector bundles and fiber bundles, universal cover of the group of homomorphisms of the circle, 57R30, piecewise linear homeomorphisms, circle bundle, Foliations in differential topology; geometric theory, PL-topology
transversely \(PL\) foliation, Topology of vector bundles and fiber bundles, universal cover of the group of homomorphisms of the circle, 57R30, piecewise linear homeomorphisms, circle bundle, Foliations in differential topology; geometric theory, PL-topology
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