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Direct sum decompositions of modules, almost trace ideals, and pullbacks of monoids

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Published/Copyright: May 18, 2006
Forum Mathematicum
From the journal Volume 18 Issue 3

Abstract

We show that a number of pullback diagrams appear naturally in the study of preordered Grothendieck groups. The passage of projective modules from a ring R to a factor ring R/I turns out to be particularly good for a certain class of ideals, which we call almost trace ideals. We generalize to arbitrary rings a result by Goodearl concerning the lattice of the directed convex subgroups of K0(R). Finally, we show that a variant (I) of the Grothendieck group of I, introduced by Quillen, has an easy description in terms of projective modules when I is an almost trace ideal.


(Communicated by Rüdiger Göbel)

* Partially supported by the DGI and the European Regional Development Fund, jointly, through Project BFM2002-01390, and by the Comissionat per Universitats i Recerca de la Generalitat de Catalunya.

† Partially supported by Ministero dell'Istruzione, dell'Università e della Ricerca (Italy) and by Departament d'Universitats, Recerca i Societat de la Informació (Generalitat de Catalunya). This paper was written during a sabbatical year of the second author at the Centre de Recerca Matemàtica (Barcelona). He acknowledges the kind hospitality received.


Received: 2004-02-02
Revised: 2004-07-14
Published Online: 2006-05-18
Published in Print: 2006-05-01

© Walter de Gruyter

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