
Monstrous dessins 3
A long while ago I promised to take you from the action by the modular group $\Gamma=PSL_2(\mathbb{Z})$ on the lattices at hyperdistance $n$ from the standard orthogonal laatice $L_1$ to the corresponding ‘monstrous’ Grothendieck dessin d’enfant. Speaking of dessins d’enfant, let me point you to the latest intriguing paper by Yuri I. Manin and Matilde […]

Chomp and the moonshine thread
Chomp is a 2player game, usually played with chocolate bars. The players take turns in choosing one chocolate block and “eat it”, together with all other blocks that are below it and to its right. There is a catch: the top left block contains poison, so the first player forced to eat it dies, that…

Farey symbols in SAGE 5.0
The sporadic second Janko group $J_2$ is generated by an element of order two and one of order three and hence is a quotient of the modular group $PSL_2(\mathbb{Z}) = C_2 \ast C_3$. This Janko group has a 100dimensional permutation representation and hence there is an index 100 subgroup $G$ of the modular group such…