The paper concerns sufficiently saturated structures M over a countable language with a unary predicate P. It is shown that if $P(M)$ is stably embedded and there are no Vaughtian pairs with respect to P, then an infinite group is interpretable over M (in an infinitary sense of ‘interpretable’). Also, it is shown that if M is $\omega$-categorical, $f\,{:}\,D\,{\longrightarrow}\,P$ is a 0-definable map with finite fibres, and $P(M)$ is stably embedded but D is not, then some infinite group is first-order interpretable over M.

Let $C_A/\Q$ be the curve $y^2 = x^5 + A$, and let $L(s, J_A)$ denote the $L$-series of its Jacobian. Under the assumption that the sign in the functional equation for $L(s, J_A)$ is $+1$, the critical value $L(1, J_A)$ is evaluated in terms of the value of a theta series for $\Q(\sqrt{5})$ depending on $A$ at a complex multiplication point coming from $\Q(\zeta_5)$.

Graham Higman proved that a finitely generated group can be embedded in a finitely presented group if and only if it has a recursively enumerable set of defining relations. The analogue for lattice-ordered groups is considered here. Clearly, the finitely generated lattice-ordered groups that can be $\ell$-embedded in finitely presented lattice-ordered groups must have recursively enumerable sets of defining relations. The converse direction is proved for a special class of lattice-ordered groups.

THEOREM. Every finitely generated Abelian lattice-ordered group that has finite rank and a recursively enumerable set of defining relations can be$\ell$-embedded in a finitely presented lattice-ordered group.

If $\xi$ is a real number, let $D(\xi)$ be the Abelian rank 2 group $\Z^2$ with order $(m,n)>0$ if and only if $m+n\xi>0$.

COROLLARY. $D(\xi)$can be$\ell$-embedded in a finitely presented lattice-ordered group if and only if$\xi$is a recursive real number.

Thus an algebraic characterisation of recursive real numbers is obtained. In particular, $\pi$ is ‘$\ell$-algebraic’ in that it can be captured by finitely many relations in this language.

Binz, Neukirch and Wenzel proved a profinite version of the Kurosh subgroup theorem. In the paper a subgroup theorem for certain profinite fundamental groups of graphs of profinite groups is shown. In particular, the case of free products with amalgamation is discussed and illustrated in the context of real function fields in one variable.

The paper continues the investigation of the Hecke structure of spaces of half-integral weight cusp forms ${S_{k + 1/2}}(4N, \chi)$, where $k$ and $N$ are positive integers with $N$ odd, and $\chi$ is an even quadratic Dirichlet character modulo $4N$. In the Hecke decomposition of these spaces, contributions are determined arising from newforms which are quadratic twists of newforms at lower levels. Combining this result with its counterpart in a previous paper regarding non-twists gives this paper's main result: necessary and sufficient conditions under which a given newform has equivalent cusp forms in ${S_{k + 1/2}}(4N, \chi)$. The result reformulates, in classical terms, the representation-theoretic conditions given by Flicker and Waldspurger. The conditions involve easily-verified information about the primes dividing the level of the newform, and about the behavior of the newform under certain quadratic twists and Atkin–Lehner involutions. The theorem is applied to give explicit examples of twisted newforms having no equivalent half-integral weight cusp forms in any space ${S_{k + 1/2}}(4N, \chi)$ as above.

The paper explores dualizing differential graded (DG) modules over DG algebras. The focus is on DG algebras that are commutative local, and finite. One of the main results established is that, for this class of DG algebras, a finite DG module is dualizing precisely when its Bass number is 1. As a corollary, one obtains that the Avramov–Foxby notion of Gorenstein DG algebras coincides with that due to Frankild and Jørgensen. One other key result is that, under suitable hypotheses, any two dualizing DG modules are quasiisomorphic up to a suspension. In addition, it is established that a number of naturally occurring DG algebras possess dualizing DG modules.

The number of crepant valuations of an isolated canonical singularity $0\in X:(f\,{=}\,0)\,{\subset}\,\mathbb{C}^{n}$, which is assumed to be nondegenerate with respect to its Newton polyhedron, is calculated in terms of weightings and the Newton polyhedron of $f$.

Let $p$ be a prime number, $F$ a number field, and ${\cal H}_F^n$ the set of all unramified cyclic extensions over $F$ of degree $p$ having a relative normal integral basis. When $\z_p \in F^{\times}$, Childs determined the set ${\cal H}_F^n$ in terms of Kummer generators. When $p=3$ and $F$ is an imaginary quadratic field, Brinkhuis determined this set in a form which is, in a sense, analogous to Childs's result. The paper determines this set for all $p \ge 3$ and $F$ with $\z_p \not\in F^{\times}$ (and satisfying an additional condition), using the result of Childs and a technique developed by Brinkhuis. Two applications are also given.

Goldston and Montgomery proved that the strong pair correlation conjecture and two second moments of primes in short intervals are equivalent to each other under the Riemann hypothesis. The paper obtains the second main terms for each of the above, and it is shown that they are almost equivalent to each other.

A set $A\subseteq \{1,2,\ldots,n\}$ is said to be $k$-separated if, when considered on the circle, any two elements of $A$ are separated by a gap of size at least $k$.

A conjecture due to Holroyd and Johnson that an analogue of the Erdős–Ko–Rado theorem holds for $k$-separated sets is proved. In particular, the result holds for the vertex-critical subgraph of the Kneser graph identified by Schrijver, the collection of separated sets. A version of the Erdős–Ko–Rado theorem for weighted $k$-separated sets is also given.

Introducing the framework of pseudo-motivic homology, the paper finishes the proof that the Brauer–Manin obstruction is the only obstruction to the local–global principle for zero-cycles on a Severi–Brauer fibration of squarefree index over a smooth projective curve over a number field, provided that the Tate–Shafarevich group of the Jacobian of the base curve is finite. More precisely, for such a variety the Chow group of global zero-cycles is dense in the subgroup of collections of local cycles that are orthogonal to the (cohomological) Brauer group of the variety.

Inspired by the work of Bloch and Kato in [2], David Burns constructed several ‘equivariant Tamagawa invariants’ associated to motives of number fields. These invariants lie in relative $K$-groups of group-rings of Galois groups, and in [3] Burns gave several conjectures (see Conjecture 3.1) about their values. In this paper I shall verify Burns' conjecture concerning the invariant $T\Omega^{\rm loc}( N/{\bf Q},1)$ for some families of quaternion extensions $N/{\bf Q}$. Using the results of [9] I intend in a subsequent paper to verify Burns' conjecture for those families of quaternion fields which are not covered here.

It is shown that a $\scriptstyle \overline {\mathbb Q}$-curve of genus $g$ and with stable reduction (in some generalized sense) at every finite place outside a finite set $S$ can be defined over a finite extension $L$ of its field of moduli $K$ depending only on $g$, $S$ and $K$. Furthermore, there exist $L$-models that inherit all places of good and stable reduction of the original curve (except possibly for finitely many exceptional places depending on $g$, $K$ and $S$). This descent result yields this moduli form of the Shafarevich conjecture: given $g$, $K$ and $S$ as above, only finitely many $K$-points on the moduli space ${\cal M}_g$ correspond to $\scriptstyle \overline {\mathbb Q}$-curves of genus $g$ and with good reduction outside $S$. Other applications to arithmetic geometry, like a modular generalization of the Mordell conjecture, are given.

Let $k$ be a field of characteristic zero, $f(X,Y), g(X,Y)\,{\in}\,k[X,Y]$, $g(X,Y)\,{\notin}\,(X,Y)$ and $d\,{:=} g(X,Y)\,{\partial}/ {\partial X}+f(X,Y)\,{\partial}/{\partial Y}$. A connection is established between the $d$-simplicity of the local ring $k[X,Y]_{(X,Y)}$ and the transcendency of the solution in $tk[[t]]$ of the algebraic differential equation $g(t,y(t))\,{\cdot}\, ({\partial}/{\partial t})y(t)=f(t,y(t))$. This connection is used to obtain some interesting results in the theory of the formal power series and to construct new examples of differentially simple rings.

A partition of the class of all Hermite–Biehler entire functions of finite order into subclasses ${\cal P}_\kappa$ is introduced. A given function $E(z)$ belongs to ${\cal P}_\kappa$ if and only if $-z^{-1}\log E(z)\in{\mc N}_\kappa$, where the class ${\mc N}_\kappa$ is a well studied family of meromorphic functions on the upper half plane, which originates from operator theoretic problems. It is also proved that the subclasses ${\cal P}_\kappa$ are stable under bounded type perturbation.

Let $G$ be a group and $K$ a field. For any finite-dimensional $KG$-module $V$ and any positive integer $n$, let $L^n(V)$ denote the $n$th homogeneous component of the free Lie $K$-algebra generated by (a basis of) $V$. Then $L^n(V)$ can be considered as a $KG$-module, called the $n$th Lie power of $V$. The paper is concerned with identifying this module up to isomorphism. A simple formula is obtained which expresses $L^n(V)$ in terms of certain linear functions on the Green ring. When $n$ is not divisible by the characteristic of $K$ these linear functions are Adams operations. Some results are also obtained which clarify the relationship between Adams operations defined by means of exterior powers and symmetric powers and operations introduced by Benson. Some of these results are put into a more general setting in an appendix by Stephen Donkin.

The paper shows that for every positive integer $p > 2$, there exists a compact non-orientable surface of genus $p$ with at least $4p$ automorphisms if $p$ is odd, or at least $8\,(p-2)$ automorphisms if $p$ is even, with improvements for odd $p\not\equiv 3$ mod 12. Further, these bounds are shown to be sharp (in that no larger group of automorphisms exists with genus $p$) for infinitely many values of $p$ in each congruence class modulo 12, with the possible (but unlikely) exception of 3 mod 12.

For an artin algebra $\Lambda$, cotorsion pairs are studied for the category ${\rm mod}\Lambda$ of finitely presented $\Lambda$-modules and for the category ${\rm Mod}\Lambda$ of all $\Lambda$-modules. It is shown that every cotorsion pair for ${\rm mod}\Lambda$ induces a cotorsion pair for ${\rm Mod}\Lambda$. This has some interesting applications, even for the category of finitely presented modules. Another theme of the paper is the interplay between cotorsion and torsion pairs. This leads to a conjecture which is an analogue of the telescope conjecture in stable homotopy theory.

It is shown that Alperin's weight conjecture is equivalent to the existence of contractible chain complexes whose entries have the right dimension coming from some of the alternating sum formulations. It is conjectured that for the other formulations and for Dade's ordinary conjecture, there also exist such contractible chain complexes.

The first example of a non-finitely based variety of centre-by-abelian-by-nilpotent groups was found in 1995. This example has an infinite exponent but it can be seen that the method used to construct it also gives a variety that has an exponent of 128. Later it was proved that there exists a variety with similar properties but with an exponent of 32. The paper constructs a non-finitely based variety of centre-by-abelian-by-nilpotent groups which has an exponent of 8.