The **width** of the cusp $\infty$
for the group $\Gamma$ is the smallest number $w$ such that $T^w=\left(\begin{matrix}1&w\\0&1\end{matrix}\right)\in\Gamma$. Furthermore, for a general $x\in\mathbb{P}^1(\mathbb{Q})$ and $\gamma\in\Gamma$ such that $\gamma\infty=x$, we define the **width** of $x$ for $\Gamma$ to be the width of $\infty$ for $\gamma^{-1}\Gamma\gamma$.

Note that $T=\left(\begin{matrix}1&1\\0&1\end{matrix}\right)$ is one of the **generators** of the modular group $\textrm{SL}_2(\mathbb{Z})$.

**Knowl status:**

- Review status: reviewed
- Last edited by David Farmer on 2019-04-29 09:40:07

**Referred to by:**

**History:**(expand/hide all)

- 2019-04-29 09:40:07 by David Farmer (Reviewed)
- 2019-04-10 01:21:14 by Alex J. Best
- 2019-04-09 23:05:11 by David Farmer (Reviewed)
- 2018-12-13 05:51:09 by Andrew Sutherland

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