| Data: |
2004 |
| Resum: |
A pair of symmetries (σ, τ ) of a Riemann surface X is said to be perfect if their product belongs to the derived subgroup of the group Aut+(X) of orientation preserving automorphisms. We show that given g 6= 2, 3, 5, 7 there exists a Riemann surface X of genus g admitting a perfect pair of symmetries of certain topological type. On the other hand we show that a twist can be written as a product of two symmetries of the same type which leads to a decomposition of a twist as a product of two commutators: one from M0 which entirely lives on a Riemann surface and one from M±0 . As a result we obtain the perfectness of the mapping class group Mg for such g relying only on results of Birman [1] but not on influential paper of Powell [6] nor on Johnson's rediscovery of Dehn lantern relation [3] and nor on recent results of Korkmaz-Ozbagci [4] who found explicit presentation of a twist as a product of two commutators. |
| Drets: |
Tots els drets reservats.  |
| Llengua: |
Anglès |
| Document: |
Article ; recerca ; Versió publicada |
| Matèria: |
Mapping class group ;
Symmetries of Riemann surfaces |
| Publicat a: |
Publicacions matemàtiques, V. 48 N. 1 (2004) , p. 103-106, ISSN 2014-4350 |
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