We study a super group of the group of Riordan arrays, where the elements of the group are given by a triple of power series. We show that certain subsets are subgroups, and we identify a normal subgroup whose cosets correspond to Riordan arrays. We give an example of an almost-Riordan array that has been studied in the context of Hankel and Hankel plus Toepliz matrices, and we show that suitab...

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.

for some n , acting primitively on the set of vertices. This forms a part of the programme for the classification of all finite primitive distance transitive graphs begun in [76]; for in [76] this classification is reduced to the determination of all such graphs whose automorphism group G is either almost simple (that is, T o f f S Aut T for some nonabelian simple group T ) or affine (that is, ...

In a group testing scheme, a set of tests is designed to identify a small number t of defective items among a large set (of size N ) of items. In the non-adaptive scenario the set of tests has to be designed in one-shot. In this setting, designing a testing scheme is equivalent to the construction of a disjunct matrix, an M × N matrix where the union of supports of any t columns does not contai...

We study the existence of quasi-representations of discrete groups G into unitary groups U(n) that induce prescribed partial maps K0(C ∗(G)) → Z on the K-theory of the group C*-algebra of G. We give conditions for a discrete group G under which the K-theory group of the classifying space BG consists entirely of almost flat classes.

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...