<p>For a connected orientable hyperbolic surface <i>S</i> without boundary and of finite topological type, the Johnson kernel <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathcal {K}(S)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">K</mi> <mo stretchy="false">(</mo> <mi>S</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is the subgroup of the mapping class group of <i>S</i> generated by Dehn twists about separating simple closed curves on <i>S</i>. We prove that <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\mathcal {K}(S)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">K</mi> <mo stretchy="false">(</mo> <mi>S</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is generated by the Dehn twists about separating simple closed curves on <i>S</i> bounding either: a closed subsurface of genus 1 or 2; a closed subsurface of genus 1 minus one point; a closed disc minus two points.</p>

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A generating set for the Johnson kernel

  • Marco Boggi

摘要

For a connected orientable hyperbolic surface S without boundary and of finite topological type, the Johnson kernel \(\mathcal {K}(S)\) K ( S ) is the subgroup of the mapping class group of S generated by Dehn twists about separating simple closed curves on S. We prove that \(\mathcal {K}(S)\) K ( S ) is generated by the Dehn twists about separating simple closed curves on S bounding either: a closed subsurface of genus 1 or 2; a closed subsurface of genus 1 minus one point; a closed disc minus two points.