The first almost free Whitehead group

The First Almost Free Whitehead Group Sh914

Assume G.C.H. and κ is the first uncountable cardinal such that there is a non-free κ-free abelian Whitehead group of cardinality κ. We prove that if all κ-free Abelian group of cardinality κ are Whitehead then κ is necessarily an inaccessible cardinal.

The Whitehead group of (almost) extra-special p-groups with p odd

Let p be an odd prime number. We describe the Whitehead group of all extra-special and almost extra-special p-groups. For this we compute, for any finite p-group P , the subgroup Cl1(ZP ) of SK1(ZP ), in terms of a genetic basis of P . We also introduce a deflation map Cl1(ZP ) → Cl1 ( Z(P/N) ) , for a normal subgroup N of P , and show that it is always surjective. Along the way, we give a new ...

Group Signatures with Almost-for-Free Revocation

Group signatures are a central cryptographic primitive where users can anonymously and accountably sign messages in the name of a group they belong to. Several efficient constructions with security proofs in the standard model (i.e., without the random oracle idealization) appeared in the recent years. However, like standard PKIs, group signatures need an efficient revocation system to be pract...

The Whitehead Categorical Group of Derivations

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 ...

The Whitehead First Lemma for Alternative