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We establish braided tensor equivalences among module categories over the twisted quantum double of a finite group defined by an extension of a group over(G, -) by an abelian group, with 3-cocycle inflated from a 3-cocycle on over(G, -). We also prove that the canonical ribbon structure of the module category of any twisted quantum double of a finite group is preserved by braided tensor equivalences. We give two main applications: first, if G is an extra-special 2-group of width at least 2, we show that the quantum double of G twisted by a 3-cocycle ω is gauge equivalent to a twisted quantum double of an elementary abelian 2-group if, and only if, ω2 is trivial; second, we discuss the gauge equivalence classes of twisted quantum doubles of groups of order 8, and classify the braided tensor equivalence classes of these quasi-triangular quasi-bialgebras. It turns out that there are exactly 20 such equivalence classes. © 2006 Elsevier Inc. All rights reserved.

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Journal of Algebra

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