A theorem of Maranda [1, Section 30] states that if F is a finite group, p is a prime and pe exactly divides [mid ]F[mid ], then a ℤpF-lattice M is determined up to isomorphism by its finite quotient M/pe+1M. If M is a free ℤp-module of rank d, this is equivalent to saying that representations of F in GLd(ℤp) are determined up to equivalence by their images modulo pe+1.

Soient F un corps commutatif localement compact non archimédien et ψ un caractère additif non trivial de F. Soient σ une représentation du groupe de Weil–Deligne de F, et ψσˇ sa contragrédiente. Nous calculons le facteur ε(σ[otimes ]σˇ, ψ, ½). De manière analogue, nous calculons le facteur ε(π×πˇ, ψ, ½) pour toute représentation admissible irréductible π de GLn(F). En conséquence, si F est de caractéristique nulle et si σ et π se correspondent par la correspondance de Langlands construite par M. Harris, ou celle construite par les auteurs, alors les facteurs ε(σ[otimes ]σˇ, ψ, s) et ε(π×πˇ, ψ, s) sont égaux pour tout nombre complexe s.

Let F be a non-Archimedean local field and ψa non-trivial additive character of F. Let σ be a representation of the Weil–Deligne group of F and σˇ its contragredient representation. We compute ε(σ[otimes ]σˇ, ψ, ½). Analogously, we compute ε(π×πˇ, ψ, ½) for all irreducible admissible representations π of GLn(F). Consequently, if F has characteristic zero, and σ, π correspond via the Langlands correspondence established by M. Harris or the correspondence constructed by the authors, then we have ε(σ[otimes ]σˇ, ψ, s) = ε(π×πˇ, ψ, s) for all s∈[Copf ].

Let u be a bounded, uniformly continuous, mild solution of an inhomogeneous Cauchy problem on R+: u′(t)=Au(t)+ϕ(t) (t[ges ]0). Suppose that u has uniformly convergent means, σ(A)∩iR is countable, and ϕ is asymptotically almost periodic. Then u is asymptotically almost periodic. Related results have been obtained by Ruess and Vũ, and by Basit, using different methods. A direct proof is given of a Tauberian theorem of Batty, van Neerven and Räbiger, and applications to Volterra equations are discussed.

Let K be a compact subset of ℝn, 0[les ]s[les ]n. Let Ps0, [Pscr ]s denote s-dimensional packing premeasure and measure, respectively. We discuss in this paper the relation between Ps0 and [Pscr ]s. We prove: if Ps0(K)<∞, then [Pscr ]s(K) = Ps0(K); and if Ps0(K) = ∞, then for any ε>0, there exists a compact subset F of K such that [Pscr ]s(F) = Ps0(F) and [Pscr ]s(F)[ges ] [Pscr ]s(K)−ε.

Let Fn be the free group of rank n with basis x1, x2, …, xn, and let d(G) denote the minimal number of generators of the finitely generated group G. Suppose that n[ges ]d(G). There exists an exact sequence

formula here

and we may view the free abelian group R=R/R′ as a right ℤG-module by defining (rR′)g =rgϕ−1R′ for all g∈G, where gϕ−1 is any preimage of g under ϕ, and rgϕ−1 =(gϕ−1)−1r(gϕ−1), the conjugate of r by gϕ−1. We call R the relation module of G associated with the presentation (1), and say that R has ambient rank n. Furthermore, we call the group Fn/R′ the free abelianized extension of G associated with (1).

As a special case of a well-known conjecture of Artin, it is expected that a system of R additive forms of degree k, say

formula here

with integer coefficients aij, has a non-trivial solution in ℚp for all primes p whenever

formula here

Here we adopt the convention that a solution of (1) is non-trivial if not all the xi are 0. To date, this has been verified only when R=1, by Davenport and Lewis [4], and for odd k when R=2, by Davenport and Lewis [7]. For larger values of R, and in particular when k is even, more severe conditions on N are required to assure the existence of p-adic solutions of (1) for all primes p. In another important contribution, Davenport and Lewis [6] showed that the conditions

formula here

are sufficient. There have been a number of refinements of these results. Schmidt [13] obtained N[Gt ]R2k3 log k, and Low, Pitman and Wolff [10] improved the work of Davenport and Lewis by showing the weaker constraints

formula here

to be sufficient for p-adic solubility of (1).

A noticeable feature of these results is that for even k, one always encounters a factor k3 log k, in spite of the expected k2 in (2). In this paper we show that one can reach the expected order of magnitude k2.

Continuing work of Duret, we treat the relation between isomorphism and elementary equivalence of function fields over algebraically closed fields. For function fields of curves, these are ‘usually’ the same, but in characteristic zero, for elliptic curves with complex multiplication, a weak variant of elementary equivalence of their function fields corresponds to isomorphism of the endomorphism rings of the curves, not to isomorphism of the curves themselves.

In iteration theory of rational functions, it is well known that any Fatou component is mapped onto another in an n-to-1 manner, and that periodic components are simply, doubly or infinitely connected.

For meromorphic functions, the situation is much more complicated. Using Ahlfors' theory of covering surfaces, we prove that Fatou components are mapped ‘nearly’ onto others, and that periodic components are again simply, doubly or infinitely connected. Instead of considering meromorphic functions with only one essential singularity, we allow countable sets of singularities and partly even sets of logarithmic capacity zero.

It remains open whether doubly connected periodic components of meromorphic functions with only one singularity are necessarily Herman rings (as holds for rational functions). However, there is a function with two singularities and a doubly connected periodic component which is not an Herman ring.

We give a condition for an exact functor between triangulated categories to be an equivalence. Applications to Fourier–Mukai transforms are discussed. In particular, we obtain a large number of such transforms for K3 surfaces.

In this paper the authors develop a new approach to the problem of ‘propagation of smallness’ for harmonic functions in arbitrary domains, in ℝn (n[ges ]2). The main result of this paper is a certain logarithmic-convexity relation for the L2-norms of harmonic functions. As a consequence, new kinds of uniqueness results for harmonic functions are obtained. The method works also for analytic functions in [Copf ], with Lp-norms (p>0).

By a Kleinian group we mean a discrete subgroup of PSL(2, [Copf ]). We prove that abelian subgroups of finitely generated Kleinian groups are separable. In other words, if M=ℍ3/Γ is a hyperbolic 3-orbifold, with Γ finitely generated, then abelian subgroups of Γ are separable in Γ.

A regular 2-complex has a group of cellular automorphisms which is transitive on 2-cells. Let p be an odd prime. By generalizing an example of Floyd and Parry [5], we obtain infinite families of compact, aspherical, regular 2-complexes with Euler characteristic p and infinite hyperbolic fundamental group.

The global and local topological zeta functions are singularity invariants associated to a polynomial f and its germ at 0, respectively. By definition, these zeta functions are rational functions in one variable, and their poles are negative rational numbers. In this paper we study their poles of maximal possible order. When f is non-degenerate with respect to its Newton polyhedron, we prove that its local topological zeta function has at most one such pole, in which case it is also the largest pole; we give a similar result concerning the global zeta function. Moreover, for any f we show that poles of maximal possible order are always of the form −1/N with N a positive integer.

The following result is established.

THEOREM. Let G be a periodic, residually finite group with all subgroups sub-normal. Then G is nilpotent.

The well-known groups of Heineken and Mohamed [1] show that the hypothesis of residual finiteness cannot be omitted here, while examples in [5] show that a residually finite group with all subgroups subnormal need not be nilpotent. The proof of the Theorem will use the results of Möhres that a group with all subgroups subnormal is soluble [3] and that a periodic hypercentral group with all subgroups subnormal is nilpotent [4]. Borrowing an idea from [2], the plan is to construct certain subgroups H and K that intersect trivially, and to show that the subnormality of both leads to a contradiction.

In the early 1930s, Wiener proved that if f(x) is a strictly positive periodic function whose Fourier series is absolutely convergent, then the Fourier series of g(x)=1/f(x) is also absolutely convergent [8, pp. 10–14]. This phenomenon can be easily understood nowadays using Banach algebra techniques (see, for example, [4, pp. 202–203]). In fact, these techniques allow us to study the absolute convergence of g(x)=F(f(x)), where F is holomorphic in an open subset of [Copf ] that contains the range of f(x) (for x∈ℝ). In this context, Wiener's original problem corresponds to the choice F(z)=1/z.

In this work we want to analyse the constraints on the simultaneous rate of vanishing of the Fourier coefficients fˆ(n) and ĝ(n) as n→∞. We shall focus on g=1/f, but we shall also study the general case g=F(f). In either case, there are obviously no constraints when f is a constant function.

Although this problem does not seem to be directly related to uncertainty inequalities for the Fourier Transform, we observe that there are some analogies, both in the nature of the results and in the proof techniques. The general fact with which we are dealing is that fˆ(n) and ĝ(n) cannot vanish too quickly at the same time as n→∞, unless f(x) is constant. The general fact that underlies uncertainty inequalities is that a non-periodic function ϕ(x) and its Fourier Transform ϕcirc;(u) cannot vanish too quickly at the same time as x→∞ and u→∞, unless ϕ(x) is zero (almost everywhere). For a simple introduction to some aspects of uncertainty inequalities, see [5]; for a thorough and recent introduction to this vast subject, see [3].

Let δ be a coaction of a locally compact group G on a C*-algebra A. We show that if I is a δ-invariant ideal in A, then 0 → I×δIG → A×δG → (A/I)×δIG → 0 for full crossed products, as Landstad et al. have done for spatial crossed products by coactions. We prove that for suitable coactions, the crossed products of C0(X)-algebras are again C0(X)-algebras, and the crossed products of continuous C*-bundles by a locally compact group are again continuous C*-bundles.

We show that all derivations from the group algebra [lscr ]1(G) of a free group into its nth dual, where n is a positive even integer, are inner. Combined with the known result for odd values of n, this shows that these algebras are permanently weakly amenable.

We study the Čerednik–Drinfeld p-adic uniformization of certain Atkin–Lehner quotients of Shimura curves over ℚ. We use it to determine over which local fields they have rational points and divisors of a given degree. Using a criterion of Poonen and Stoll, we show that the Shafarevich–Tate group of their jacobians is not of square order for infinitely many cases.

We prove that if n>66 and (n, 30) = 1, then there exist uncountably many infinite simple (2, 3, n)- groups, that is, groups generated by a pair of elements x, y, say, where the orders of x, y and xy are 2, 3 and n, respectively. This extends previous results of Schupp and the authors.

These results are used to prove the existence of subgroups of the modular group with special arithmetic properties.

Throughout this paper, X will denote a Banach space, S=S(X) and B=B(X) will be the unit sphere and the closed unit ball of X, respectively, and [Gscr ]=[Gscr ](X) will stand for the group of all surjective linear isometries on X. Unless explicitly stated otherwise, all Banach spaces will be assumed to be real. Nevertheless, by passing to real structures, the results remain true for complex spaces.