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A+ CATEGORY SCIENTIFIC UNIT

Dehn twists on nonorientable surfaces

Volume 189 / 2006

Michał Stukow Fundamenta Mathematicae 189 (2006), 117-147 MSC: Primary 57N05; Secondary 20F38, 57M99. DOI: 10.4064/fm189-2-3

Abstract

Let be the Dehn twist about a circle a on an orientable surface. It is well known that for each circle b and an integer n, I(t_a^n(b),b)=|n|I(a,b)^2, where I(\cdot,\cdot) is the geometric intersection number. We prove a similar formula for circles on nonorientable surfaces. As a corollary we prove some algebraic properties of twists on nonorientable surfaces. We also prove that if {\cal M}(N) is the mapping class group of a nonorientable surface N, then up to a finite number of exceptions, the centraliser of the subgroup of {\cal M}(N) generated by the twists is equal to the centre of {\cal M}(N) and is generated by twists about circles isotopic to boundary components of N.

Authors

  • Michał StukowInstitute of Mathematics
    University of Gdańsk
    Wita Stwosza 57
    80-952 Gdańsk, Poland
    e-mail

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