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Algebraic homotopy classes of rational functions

Christophe Cazanave (2012)

Annales scientifiques de l'École Normale Supérieure

Let  k be a field. We compute the set 𝐏 1 , 𝐏 1 N ofnaivehomotopy classes of pointed k -scheme endomorphisms of the projective line 𝐏 1 . Our result compares well with Morel’s computation in [11] of thegroup 𝐏 1 , 𝐏 1 𝐀 1 of  𝐀 1 -homotopy classes of pointed endomorphisms of  𝐏 1 : the set 𝐏 1 , 𝐏 1 N admits an a priori monoid structure such that the canonical map 𝐏 1 , 𝐏 1 N 𝐏 1 , 𝐏 1 𝐀 1 is a group completion.

Algebraic leaves of algebraic foliations over number fields

Jean-Benoît Bost (2001)

Publications Mathématiques de l'IHÉS

We prove an algebraicity criterion for leaves of algebraic foliations defined over number fields. Namely, consider a number field K embedded in C , a smooth algebraic variety X over K , equipped with a K - rational point P , and F an algebraic subbundle of the its tangent bundle T X , defined over K . Assume moreover that the vector bundle F is involutive, i.e., closed under Lie bracket. Then it defines an holomorphic foliation of the analytic manifold X ( C ) , and one may consider its leaf F through P . We prove...

Algebraic loop groups and moduli spaces of bundles

Gerd Faltings (2003)

Journal of the European Mathematical Society

We study algebraic loop groups and affine Grassmannians in positive characteristic. The main results are normality of Schubert-varieties, the construction of line-bundles on the affine Grassmannian, and the proof that they induce line-bundles on the moduli-stack of torsors.

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