Book contents
- Frontmatter
- Contents
- List of participants at the conference
- Introduction
- Abstracts of the talks
- Noncongruence Subgroups, Covers and Drawings
- Dessins d'enfants on the Riemann sphere
- Dessins from a geometric point of view
- Maps, Hypermaps and Triangle Groups
- Fields of definition of some three point ramified field extensions
- On the classification of plane trees by their Galois orbit
- Triangulations
- Dessins d'enfant and Shimura varieties
- Horizontal divisors on arithmetic surfaces associated with Belyi uniformizations
- Algebraic representation of the Teichmüller spaces
- On the embedding of Gal(ℚ̅/ℚ) into GT
- Appendix: The action of the absolute Galois group on the moduli spaces of spheres with four marked points
- The Grothendieck-Teichmüller group and automorphisms of braid groups
- Moore and Seiberg equations, topological field theories and Galois theory
Noncongruence Subgroups, Covers and Drawings
Published online by Cambridge University Press: 05 July 2011
- Frontmatter
- Contents
- List of participants at the conference
- Introduction
- Abstracts of the talks
- Noncongruence Subgroups, Covers and Drawings
- Dessins d'enfants on the Riemann sphere
- Dessins from a geometric point of view
- Maps, Hypermaps and Triangle Groups
- Fields of definition of some three point ramified field extensions
- On the classification of plane trees by their Galois orbit
- Triangulations
- Dessins d'enfant and Shimura varieties
- Horizontal divisors on arithmetic surfaces associated with Belyi uniformizations
- Algebraic representation of the Teichmüller spaces
- On the embedding of Gal(ℚ̅/ℚ) into GT
- Appendix: The action of the absolute Galois group on the moduli spaces of spheres with four marked points
- The Grothendieck-Teichmüller group and automorphisms of braid groups
- Moore and Seiberg equations, topological field theories and Galois theory
Summary
The theory of congruence subgroups, more precisely the theory of the action of congruence subgroups of the modular group on the upper half plane, is an area of mathematics in which the mathematical structure is well understood and wonderfully intricate, and beautiful numbers appear as if by magic (see for instance [GZ]). When one turns to noncongruence subgroups, the mathematical structure must be built with fewer bricks, since in particular the Hecke theory is missing, but though the structure is more mysterious it seems to be almost as rich, and the ‘ballet of numbers’ continues to be just as beautiful. There is an enormous literature on the action of general discontinuous groups on the upper half plane; and there is an enormous literature concerned with the arithmetic theory of the action of congruence subgroups of the modular group; in contrast, the arithmetic theory of subgroups which are not congruence subgroups is surprisingly little developed. In a neighbouring area, there is a beautiful corpus of recent work concerned with the arithmetic of Galois coverings of the projective line, ramified in a prescribed way above a finite set of places; a motivation for this has been its application to the inverse Galois problem.
- Type
- Chapter
- Information
- The Grothendieck Theory of Dessins d'Enfants , pp. 25 - 46Publisher: Cambridge University PressPrint publication year: 1994
- 17
- Cited by