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arXiv · 1911.06717

Combinatorial description of the principal congruence subgroup $γ$(2) in SL(2, z)

Flavien Mabilat
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Abstract

We characterize sequences of positive integers (c 1 , c 2 , ..., cn) for which the (2 x 2)-matrix c 1 --1 1 0 $\times$ $\times$ $\times$ cn --1 1 0 belongs to the principal congruence subgroup of level 2 in SL(2, Z). The answer is given in terms of dissections of a convex n-gon into a mixture of triangles and quadrilaterals.

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Flavien Mabilat. 2022-02-21. Combinatorial description of the principal congruence subgroup $γ$(2) in SL(2, z). https://arxiv.org/abs/1911.06717

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