>>425 補足

突然ですが
遠アーベルでは、Belyi's theorem（下記)が、”Grothendieck to develop his theory of dessins d'enfant”につながったのです
こういう小さな積み重ねも大事です

ちょうど、Rydberg formula（下記)の小さな研究が
Niels Bohrらの前期量子力学の建設に繋がったようにね

https://en.wikipedia.org/wiki/Belyi%27s_theorem
Belyi's theorem
In mathematics, Belyi's theorem on algebraic curves states that any non-singular algebraic curve C, defined by algebraic number coefficients, represents a compact Riemann surface which is a ramified covering of the Riemann sphere, ramified at three points only.
This is a result of G. V. Belyi from 1979. At the time it was considered surprising, and it spurred Grothendieck to develop his theory of dessins d'enfant, which describes nonsingular algebraic curves over the algebraic numbers using combinatorial data.
Contents
1 Quotients of the upper half-plane
2 Belyi functions
3 Applications
Quotients of the upper half-plane
It follows that the Riemann surface in question can be taken to be
H/Γ
with H the upper half-plane and Γ of finite index in the modular group, compactified by cusps. Since the modular group has non-congruence subgroups, it is not the conclusion that any such curve is a modular curve.

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