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Intersecting a plane with algebraic subgroups of multiplicative groups

Enrico Bombieri, David Masser, Umberto Zannier (2008)

Annali della Scuola Normale Superiore di Pisa - Classe di Scienze

Consider an arbitrary algebraic curve defined over the field of all algebraic numbers and sitting in a multiplicative commutative algebraic group. In an earlier article from 1999 bearing almost the same title, we studied the intersection of the curve and the union of all algebraic subgroups of some fixed codimension. With codimension one the resulting set has bounded height properties, and with codimension two it has finiteness properties. The main aim of the present work is to make a start on such...

Intersection cohomology of reductive varieties

Roy Joshua, Michel Brion (2004)

Journal of the European Mathematical Society

We extend the methods developed in our earlier work to algorithmically compute the intersection cohomology Betti numbers of reductive varieties. These form a class of highly symmetric varieties that includes equivariant compactifications of reductive groups. Thereby, we extend a well-known algorithm for toric varieties.

Intersection de courbes et de sous-groupes et problèmes de minoration de hauteur dans les variétés abéliennes C.M.

Nicolas Ratazzi (2008)

Annales de l’institut Fourier

Nous prouvons un cas particulier de la conjecture suivante e Zilber-Pink, conjecture généralisant celle de Manin-Mumford  : soit X une courbe incluse dans une variété abélienne A sur ¯ , qui n’est pas incluse dans une sous-variété de torsion  ; l’intersection de X avec la réunion de tous les sous-groupes de codimension au moins 2 est finie. Nous démontrons ici le cas où A est une puissance d’une variété abélienne C.M. simple. La preuve reprend la stratégie de Rémond (suivant Bombieri-Masser-Zannier)...

Intersection of analytic curves

Tadeusz Krasiński, Krzysztof Jan Nowak (2003)

Annales Polonici Mathematici

We give a relation between two theories of improper intersections, of Tworzewski and of Stückrad-Vogel, for the case of algebraic curves. Given two arbitrary quasiprojective curves V₁,V₂, the intersection cycle V₁ ∙ V₂ in the sense of Tworzewski turns out to be the rational part of the Vogel cycle v(V₁,V₂). We also give short proofs of two known effective formulae for the intersection cycle V₁ ∙ V₂ in terms of local parametrizations of the curves.

Intersection theory and separation exponent in complex analytic geometry

Ewa Cygan (1998)

Annales Polonici Mathematici

We consider the intersection multiplicity of analytic sets in the general situation. We prove that it is a regular separation exponent for complex analytic sets and so it estimates the Łojasiewicz exponent. We also give some geometric properties of proper projections of analytic sets.

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