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Quadratic forms and singularities of genus one or two

Georges Dloussky (2011)

Annales de la faculté des sciences de Toulouse Mathématiques

We study singularities obtained by the contraction of the maximal divisor in compact (non-kählerian) surfaces which contain global spherical shells. These singularities are of genus 1 or 2, may be ℚ -Gorenstein, numerically Gorenstein or Gorenstein. A family of polynomials depending on the configuration of the curves computes the discriminants of the quadratic forms of these singularities. We introduce a multiplicative branch topological invariant which determines the twisting coefficient of a non-vanishing...

Quadro-quadric Cremona transformations in low dimensions via the  J C -correspondence

Luc Pirio, Francesco Russo (2014)

Annales de l’institut Fourier

It has been previously established that a Cremona transformation of bidegree (2,2) is linearly equivalent to the projectivization of the inverse map of a rank 3 Jordan algebra. We call this result the “ J C -correspondence”. In this article, we apply it to the study of quadro-quadric Cremona transformations in low-dimensional projective spaces. In particular we describe new very simple families of such birational maps and obtain complete and explicit classifications in dimension 4 and 5.

Quasi-lines and their degenerations

Laurent Bonavero, Andreas Höring (2007)

Annali della Scuola Normale Superiore di Pisa - Classe di Scienze

In this paper we study the structure of manifolds that contain a quasi-line and give some evidence towards the fact that the irreducible components of degenerations of the quasi-line should determine the Mori cone. We show that the minimality with respect to a quasi-line yields strong restrictions on fibre space structures of the manifold.

Quelques propriétés des transformations birationnelles du plan projectif complexe, une histoire pour S.

Julie Déserti (2008/2009)

Séminaire de théorie spectrale et géométrie

On présente certaines (malheureusement pas toutes) propriétés connues du groupe de Cremona en faisant, lorsque c’est possible, un parallèle avec le groupe des automorphismes polynomiaux de ℂ 2 . Les propriétés abordées seront essentiellement de nature algébrique : théorème de génération, sous-groupes finis, sous-groupes de type fini, description du groupe d’automorphismes du groupe de Cremona,... mais aussi de nature dynamique : classification des transformations birationnelles, centralisateur, dynamique...

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