منابع مشابه
A Non-reflexive Whitehead Group
We prove that it is consistent that there is a non-reflexive Whitehead group, in fact one whose dual group is free. We also prove that it is consistent that there is a group A such that Ext(A,Z) is torsion and Hom(A,Z) = 0. As an application we show the consistency of the existence of new co-Moore spaces.
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Given a categorical crossed module H→ G, where G is a group, we show that the category of derivations, Der(G,H), from G into H has a natural monoidal structure. We introduce the Whitehead categorical group of derivations as the Picard category of Der(G,H) and then we characterize the invertible derivations, with respect to the tensor product, in this monoidal category. 2000 Mathematics Subject ...
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We give an explicit formula for Whitehead group of a threedimensional crystallographic group Γ in terms of the Whitehead groups of the virtually infinite cyclic subgroups of Γ. 0 Introduction The K-theory of integral group rings of crystallographic groups has been studied by Connolly and Koźniewski [8], Farrell and Hsiang [10], Farrell and Jones [11], Lück and Stamm [15], Quinn [20], Tsapogas [...
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Emergence has a long and controversial history. In this paper we briefly review the primary strands of the debate, paying attention to its use in the fields of philosophy of science and mind, social science and systems theory including the theory of complex systems. We argue that it is important to recognize why emergence in social systems is fundamentally different from other natural systems. ...
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ژورنال
عنوان ژورنال: Journal of Pure and Applied Algebra
سال: 2001
ISSN: 0022-4049
DOI: 10.1016/s0022-4049(99)00152-8