## Geometry & Topology

### Addendum to: Commensurations of the Johnson kernel

#### Abstract

Let $K(S)$ be the subgroup of the extended mapping class group, $Mod(S)$, generated by Dehn twists about separating curves. In our earlier paper, we showed that $Comm(K(S))≅Aut(K(S))≅Mod(S)$ when $S$ is a closed, connected, orientable surface of genus $g≥4$. By modifying our original proof, we show that the same result holds for $g≥3$, thus confirming Farb’s conjecture in all cases (the statement is not true for $g≤2$).

#### Article information

Source
Geom. Topol., Volume 12, Number 1 (2008), 97-101.

Dates
Accepted: 12 October 2007
First available in Project Euclid: 20 December 2017

https://projecteuclid.org/euclid.gt/1513800014

Digital Object Identifier
doi:10.2140/gt.2008.12.97

Mathematical Reviews number (MathSciNet)
MR2377246

Zentralblatt MATH identifier
1128.57303

Subjects
Primary: 20F36: Braid groups; Artin groups

#### Citation

Brendle, Tara E; Margalit, Dan. Addendum to: Commensurations of the Johnson kernel. Geom. Topol. 12 (2008), no. 1, 97--101. doi:10.2140/gt.2008.12.97. https://projecteuclid.org/euclid.gt/1513800014

#### References

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