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Algorithms and Classification in Groups of Piecewise-Linear Homeomorphisms

Matucci, Francesco

PhD Thesis, Cornell University, 2008

This manuscript represents the author's PhD dissertation thesis.The first part studies decision problems in Thompson's groups F,T,V and some generalizations. The simultaneous conjugacy problem is determined to be solvable for Thompson's group F and suitable larger groups of piecewise-linear homeomorphisms of the unit interval. We determine algorithms to compute roots and centralizers in these groups and to detect periodic points and their behavior by looking at a particular diagram associated to an element.
In the second part, we describe the structure of subgroups of the group of all homeomorphisms of the unit circle, with the additional requirement that they contain no non-abelian free subgroup. It is shown that in this setting the rotation number map is a group homomorphism. We give a classification of such subgroups as subgroups of certain wreath products and we show that such subgroups can exist by building examples. Similar techniques are then used to compute centralizers in these groups.