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Pairings, duality, amenability and bounded cohomology

Jacek Brodzki, Graham A. Niblo, Nick J. Wright (2012)

Journal of the European Mathematical Society

We give a new perspective on the homological characterizations of amenability given by Johnson & Ringrose in the context of bounded cohomology and by Block & Weinberger in the context of uniformly finite homology. We examine the interaction between their theories and explain the relationship between these characterizations. We apply these ideas to give a new proof of non-vanishing for the bounded cohomology of a free group.

Produits finis de commutateurs dans les C * -algèbres

Pierre de La Harpe, Georges Skandalis (1984)

Annales de l'institut Fourier

Soient A une C * -algèbre approximativement finie simple avec unité, G L 1 ( A ) le groupe des inversibles et U 1 ( A ) le groupe des unitaires de A . Nous avons défini dans un précédent travail un homomorphisme Δ T , appelé déterminant universel de A , de G L 1 ( A ) sur un groupe abélien associé à A . Nous montrons ici que, pour qu’un élément x dans G L 1 ( A ) ou dans U 1 ( A ) soit produit d’un nombre fini de commutateurs, il (faut et il) suffit que x Ker ( Δ T ) . Ceci permet en particulier d’identifier le noyau de la projection canonique K 1 ( A ) K 1 top ( A ) . On établit aussi...

Report on twisted sums of Banach spaces.

Félix Cabello, Jesús M. Fernández Castillo (1996)

Extracta Mathematicae

This note is to report some of the advances obtained as a follow-up of the book [2] on the topic of twisted sums of Banach spaces. Since this announcement is no longer enough to contain the theory being developed, we submit the interested reader to [2] and to [1], where full details and proofs shall appear.

Section spaces of real analytic vector bundles and a theorem of Grothendieck and Poly

Dietmar Vogt (2010)

Banach Center Publications

The structure of the section space of a real analytic vector bundle on a real analytic manifold X is studied. This is used to improve a result of Grothendieck and Poly on the zero spaces of elliptic operators and to extend a result of Domański and the author on the non-existence of bases to the present case.

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