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Almost Abelian regular dessins d'enfants

Ruben A. Hidalgo — 2013

Fundamenta Mathematicae

A regular dessin d'enfant, in this paper, will be a pair (S,β), where S is a closed Riemann surface and β: S → ℂ̂ is a regular branched cover whose branch values are contained in the set {∞,0,1}. Let Aut(S,β) be the group of automorphisms of (S,β), that is, the deck group of β. If Aut(S,β) is Abelian, then it is known that (S,β) can be defined over ℚ. We prove that, if A is an Abelian group and Aut(S,β) ≅ A ⋊ ℤ₂, then (S,β) is also definable over ℚ. Moreover, if A ≅ ℤₙ, then we provide explicitly...

Maximal real Schottky groups.

Rubén A. Hidalgo — 2004

Revista Matemática Iberoamericana

Let S be a real closed Riemann surfaces together a reflection τ : S ---> S, that is, an anticonformal involution with fixed points. A well known fact due to C. L. May asserts that the group K(S, τ), consisting on all automorphisms ...

Schottky uniformizations of Z actions on Riemann surfaces.

Rubén A. Hidalgo — 2005

Revista Matemática Complutense

Given a closed Riemann surface S together a group of its conformal automorphisms H ≅ Z , it is known that there are Schottky uniformizations of S realizing H. In this note we proceed to give an explicit Schottky uniformizations for each of all different topological actions of Z as group of conformal automorphisms on a closed Riemann surface.

A, A, S and S of Schottky type.

Rubén A. Hidalgo — 2002

Revista Matemática Complutense

Let H be a group of conformal automorphisms of a closed Riemann surface S, isomorphic to either of the alternating groups A or A or the symmetric groups S or S. We provide necessary and sufficient conditions for the existence of a Schottky uniformization of S for which H lifts. In particular, togheter with the previous works in Hidalgo (1994,1999), we exhaust the list of finite groups of Möbius transformations of Schottky type.

An example of degeneration on the noded Schottky space.

Rubén A. Hidalgo — 1998

Revista Matemática Complutense

In these notes we construct explicit examples of degenerations on the noded Schottky space of genus g ≥ 3. The particularity of these degenerations is the invariance under the action of a dihedral group of order 2g. More precisely, we find a two-dimensional complex manifold in the Schottky space such that all groups (including the limit ones in the noded Schottky space) admit a fixed topological action of a dihedral group of order 2g as conformal automorphisms.

Lifting di-analytic involutions of compact Klein surfaces to extended-Schottky uniformizations

Rubén A. Hidalgo — 2011

Fundamenta Mathematicae

Let S be a compact Klein surface together with a di-analytic involution κ: S → S. The lowest uniformizations of S are those whose deck group is an extended-Schottky group, that is, an extended Kleinian group whose orientation preserving half is a Schottky group. If S is a bordered compact Klein surface, then it is well known that κ can be lifted with respect to a suitable extended-Schottky uniformization of S. In this paper, we complete the above lifting property by proving that if S is a closed...

Some generalized Coxeter groups and their orbifolds.

Marcel Hagelberg;  Rubén A. Hidalgo — 1997

Revista Matemática Iberoamericana

In this note we construct examples of geometric 3-orbifolds with (orbifold) fundamental group isomorphic to a (Z-extension of a) generalized Coxeter group. Some of these orbifolds have either euclidean, spherical or hyperbolic structure. As an application, we obtain an alternative proof of theorem 1 of Hagelberg, Maclaughlan and Rosenberg in [5]. We also obtain a similar result for generalized Coxeter groups.

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