#### Volume 12, issue 1 (2008)

 Recent Issues
 The Journal About the Journal Subscriptions Editorial Board Editorial Interests Editorial Procedure Submission Guidelines Submission Page Ethics Statement Author Index To Appear ISSN (electronic): 1364-0380 ISSN (print): 1465-3060 Other MSP Journals
Addendum to: Commensurations of the Johnson kernel

### Tara E Brendle and Dan Margalit

Geometry & Topology 12 (2008) 97–101
##### Abstract

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

##### Keywords
Johnson kernel, Torelli group, automorphisms, abstract commensurator
Primary: 20F36