Timeline for Upper bound on level of a congruence subgroup of the modular group
Current License: CC BY-SA 3.0
4 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Nov 23, 2015 at 13:08 | comment | added | Jan-Christoph Schlage-Puchta | $\mathbb{H}/\Gamma$ has one point at infinity. If $\Delta<\Gamma$, then $\mathbb{H}/\Delta$ has several points $p_1, \ldots, p_k$. Each $p_i$ has a neighbourhood intersecting $c_i$ copies of $\mathbb{H}/\Gamma$, where $\sum_i c_i=(\Gamma:\Delta)$. The partition $c_1, \ldots, c_k$ of $(\Gamma:\Delta)$ is the cusp split of $\Delta$ and is easy to compute, see Millington, Subgroups of the classical modular group, J. LMS 1 (1969) 351-357. | |
| Nov 22, 2015 at 19:08 | vote | accept | Joseph Ricci | ||
| Nov 22, 2015 at 18:53 | comment | added | Joseph Ricci | Does "cusp split" mean the orbits of the rationals and infinity under the subgroup? | |
| Nov 22, 2015 at 12:57 | history | answered | Jan-Christoph Schlage-Puchta | CC BY-SA 3.0 |