- Commit
- 23b64ab8268bd62c4eb19151d1f3a9cd4654eebf
- Parent
- 7fb6fb434e092881be904180d6a92a69e9d6e764
- Author
- Pablo <pablo-pie@riseup.net>
- Date
Changed the notation for permutation groups
𝔖 → S
My M2 Memoire on mapping class groups & their representations
Changed the notation for permutation groups
𝔖 → S
2 files changed, 4 insertions, 4 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/presentation.tex | 2 | 1 | 1 |
Modified | sections/twists.tex | 6 | 3 | 3 |
diff --git a/sections/presentation.tex b/sections/presentation.tex @@ -87,7 +87,7 @@ strands. The \emph{braid group on \(n\) strands} \(B_n\) is the fundamental group \(\pi_1(C(\mathbb{D}^2, n), *)\) of the unordered configuration space \(C(\mathbb{D}^2, n) = \mfrac{C^{\operatorname{ord}}(\mathbb{D}^2, - n)}{\mathfrak{S}_n}\) of \(n\) distinct points in the interior of the disk. + n)}{S_n}\) of \(n\) distinct points in the interior of the disk. The elements of \(B_n\) are referred to as \emph{braids}. \end{definition}
diff --git a/sections/twists.tex b/sections/twists.tex @@ -207,14 +207,14 @@ Given an orientable surface \(\Sigma\) and \(x_1, \ldots, x_n \in \Sigma\degree\ denote by \(\Mod(\Sigma \setminus \{x_1, \ldots, x_n\})_{\{x_1, \ldots, x_n\}} \subset \Mod(\Sigma \setminus \{x_1, \ldots, x_n\})\) the subgroup of mapping classes \(f\) that permute \(x_1, \ldots, x_n\) -- i.e. \(f \cdot x_i = -x_{\sigma(i)}\) for some \(\sigma \in \mathfrak{S}_n\). We certainly have a +x_{\sigma(i)}\) for some \(\sigma \in S_n\). We certainly have a surjective homomorphism \(\operatorname{forget} : \Mod(\Sigma \setminus \{x_1, \ldots, x_n\})_{\{x_1, \ldots, x_n\}} \to \Mod(\Sigma)\) which ``\emph{forgets} the additional punctures \(x_1, \ldots, x_n\) of \(\Sigma \setminus \{x_1, \ldots, x_n\}\),'' but what is its kernel? To answer this question, we consider the configuration space \(C(\Sigma, n) = -\mfrac{C^{\operatorname{ord}}(\Sigma, n)}{\mathfrak{S}_n}\) of \(n\) (unordered) +\mfrac{C^{\operatorname{ord}}(\Sigma, n)}{S_n}\) of \(n\) (unordered) points in the interior of \(\Sigma\) -- where \(C^{\operatorname{ord}}(\Sigma, n) = \{ (x_1, \ldots, x_n) \in (\Sigma\degree)^n : x_i \ne x_j \ \text{for}\ i \ne j \}\). Denote \(\Homeo^+(\Sigma, \partial \Sigma)_{x_1, \ldots, x_n} = \{\phi \in \Homeo^+(\Sigma, @@ -263,7 +263,7 @@ and its long exact sequence in homotopy we then get\dots We may regard a simple loop \(\alpha \subset C(\Sigma, n)\) based at \([x_1, \ldots, x_n]\) as \(n\) disjoint curves \(\alpha_1, \ldots, \alpha_n \subset \Sigma\) with \(\alpha_i(0) = x_i\) and \(\alpha_i(1) = x_{\sigma(i)}\) for some \(\sigma \in -\mathfrak{S}_n\). The element \(\operatorname{push}([\alpha]) \in \Mod(\Sigma)\) can +S_n\). The element \(\operatorname{push}([\alpha]) \in \Mod(\Sigma)\) can then be seen as the mapping class that ``\emph{pushes} a neighborhood of \(x_{\sigma(i)}\) towards \(x_i\) along the curve \(\alpha_i^{-1}\),'' as shown in Figure~\ref{fig:push-map} for the case \(n = 1\). Indeed, this goes to