- Commit
- 111f27939792e691654b57cfb6560ce6f31b4633
- Parent
- a116b7ad2e3a23bb6a96e4387778553202cc2c29
- Author
- Pablo <pablo-pie@riseup.net>
- Date
Fixed some spacing issues in chapter 3
My M2 Memoire on mapping class groups & their representations
Fixed some spacing issues in chapter 3
1 file changed, 21 insertions, 19 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/presentation.tex | 40 | 21 | 19 |
diff --git a/sections/presentation.tex b/sections/presentation.tex @@ -1,4 +1,4 @@ -\chapter{Relations Among Twists \& Wajnryb's Presentation} +\chapter{Relations Between Twists} Having acomplished the milestones of Theorem~\ref{thm:lickorish-gens} and Corollary~\ref{thm:humphreys-gens}, we now find ourselves ready to study some @@ -60,7 +60,7 @@ example\dots = [\tau_\alpha] + [\tau_\beta] + [\tau_\gamma] = [\tau_{\delta_1}] + [\tau_{\delta_2}] + [\tau_{\delta_3}] + [\tau_{\delta_4}] - = 4 \cdot [\tau_\alpha], + = 4 \cdot [\tau_\alpha] \] in \(\Mod(S_g^b)^\ab\). In other words, \([\tau_\alpha] = 0\) and thus \(\Mod(S_g^b)^\ab = 0\). @@ -73,14 +73,14 @@ example\dots \label{fig:latern-relation-trivial-abelianization} \end{figure} -% TODO: Fix the spacing of this table We should note that in general \(\Mod(S)^\ab\) needs not be trivial. For example, in \cite[Section~5.1.3]{farb-margalit} Farb-Margalit use different presentations of \(\Mod(S_g)\) for \(g \le 2\) to show the Abelianization is given by \begin{center} - \begin{tabular}{ r|c|l } - \(g\) & \(S_g\) & \(\Mod(S_g)^\ab\) \\ + \begin{tabular}{r|c|l} + \(g\) & \(S_g\) & \(\Mod(S_g)^\ab\) \\[1pt] \hline + & & \\[-10pt] \(0\) & \(\mathbb{S}^2\) & \(0\) \\ \(1\) & \(\mathbb{T}\) & \(\mathbb{Z}/12\) \\ \(2\) & \(S_2\) & \(\mathbb{Z}/10\) \\ @@ -212,6 +212,7 @@ we get\dots around the punctures $x_1, \ldots, x_n$ of $S_{0, n}^1$.} \label{fig:braid-group-center} \end{minipage} +\smallskip To get from \(S_{0, n}^1\) to surfaces of genus \(g > 0\) we may consider the \emph{hyperelliptic involution} \(\iota : S_g \isoto S_g\) which rotates @@ -294,7 +295,7 @@ continuous bijective homomorphism we find & \cong \pi_0(\Homeo^+(S_{0, 2\ell+b}^1, \partial S_{0, 2\ell+b}^1)) \\ & = \mfrac{\Homeo^+(S_{0,2\ell+b}^1, \partial S_{0, 2\ell+b}^1)}{\simeq} \\ & = \Mod(S_{0, 2\ell+b}^1) \\ - & \cong B_{2\ell + b} + & \cong B_{2\ell + b}. \end{split} \] @@ -336,17 +337,17 @@ not isotopic \emph{through symmetric homeomorphisms}. Birman-Hilden Example~\ref{ex:braid-group-center} gives us the so called \emph{\(k\)-chain relations} in \(\SMod(S_\ell^b) \subset \Mod(S_g)\). \[ - \begin{array}{rcll} - (\sigma_1 \cdots \sigma_k)^{2k+2} = z^2 \in B_{k + 1} & - \rightsquigarrow & - (\tau_{\alpha_1} \cdots \tau_{\alpha_k})^{2k + 2} - = \tau_\delta & - \text{for } k = 2 \ell \text{ even} \\ - (\sigma_1 \cdots \sigma_k)^{k+1} = z \in B_{k + 1} & - \rightsquigarrow & - (\tau_{\alpha_1} \cdots \tau_{\alpha_k})^{k + 1} - = \tau_{\delta_1} \tau_{\delta_2} & - \text{for } k = 2 \ell + 1 \text{ odd} + \arraycolsep=1.4pt + \begin{array}{rlcrll} + (\sigma_1 \cdots \sigma_k)^{2k+2} & = z^2 \in B_{k + 1} & + \; \rightsquigarrow & + \; (\tau_{\alpha_1} \cdots \tau_{\alpha_k})^{2k + 2} & = \tau_\delta & + \; \text{for } k = 2 \ell \text{ even} \\ + (\sigma_1 \cdots \sigma_k)^{k+1} & = z \in B_{k + 1} & + \; \rightsquigarrow & + \; (\tau_{\alpha_1} \cdots \tau_{\alpha_k})^{k + 1} + & = \tau_{\delta_1} \tau_{\delta_2} & + \; \text{for } k = 2 \ell + 1 \text{ odd} \end{array} \] \end{example} @@ -416,6 +417,7 @@ we get branched double cover \(S_g \to S_{0, 2g+2}\). axis centered around the punctures of $S_{0, 2g + 1}$.} \label{fig:hyperelliptic-relation-rotation} \end{minipage} +\medskip Wajnryb used the \(k\)-chain relations and the hyperelliptic relations to derive a presentation of the mapping class group of a closed surface, @@ -425,8 +427,8 @@ which is widely considered to the the standard presentation of \begin{theorem}[Wajnryb]\label{thm:wajnryb-presentation} If \(\alpha_0, \ldots, \alpha_g\) are as in % TODO: Reference the drawing of the curves somewhere - and \(a_i = \tau_{\alpha_i} \in \Mod(S_g)\) are the Humphreys generators then - there is a presentation of \(\Mod(S_g)\) with generators \(a_0, \ldots + and \(a_i = \tau_{\alpha_i} \in \Mod(S_g)\) are the Humphreys generators, + then there is a presentation of \(\Mod(S_g)\) with generators \(a_0, \ldots a_{2g}\) subject to the following relations. \begin{enumerate} \item The disjointness relations \([a_i, a_j] = 1\) for \(\alpha_i \cdot