Throughout this paper, $G$ is a connected semisimple algebraic group defined over an algebraically closed field ${\mathbb k}$ of characteristic zero, and ${\frak g}$ is its Lie algebra.

Let $A > 0$ be an integer. The equation $x^5 - y^5 = Az^5$ was first studied by Dirichlet and Lebesgue. Lebesgue conjectured in 1843 that if $A$ has no prime divisors of the form $10k+1$, the equation has no solutions except the visible ones. Partial results were obtained by Lebesgue and by Terjanian in 1987. The purpose of the paper is to prove Lebesgue's conjecture. The main tool used is the method known as the elliptic Chabauty method.

Let $p \,{\geq}\, 3$ be a prime number, $F$ be a number field with $\zeta_p \notin F^{\times}$, and $K = F(\zeta_p)$. In a previous paper, the author proved, under some assumption on $p$ and $F$, that an unramified cyclic extension $N/F$ of degree $p$ has a normal integral basis if and only if the pushed-up extension $NK/K$ has a normal integral basis. This addendum shows that the assertion holds without the above-mentioned assumption.

The paper deals with locally finite groups $G$ having an involution $\phi$ such that $C_G(\phi)$ is of finite rank. The following theorem gives a very detailed description of such groups.

Let $G$ be a locally finite group having an involution $\phi$ such that $C_G(\phi)$ is of finite rank. Then $G/[G,\phi]$ has finite rank. Furthermore, $[G,\phi]'$ contains a characteristic subgroup $B$ such that the following hold.

(1) $B$ is a product of finitely many subgroups normal in $[G,\phi]$ isomorphic to either PSL$(2,K)$ or SL$(2,K)$ for some infinite locally finite fields $K$ of odd characteristic.

(2) $[G,\phi]'/B$ has finite rank.

A profinite group $G$ of finite cohomological dimension with (topologically) finitely generated closed normal subgroup $N$ is studied. If $G$ is pro-$p$ and $N$ is either free as a pro-$p$ group or a Poincaré group of dimension 2 or analytic pro-$p$, it is shown that $G/N$ has virtually finite cohomological dimension ${\rm cd}(G)\,{-}\,{\rm cd}(N)$. Some other cases when $G/N$ has virtually finite cohomological dimension are also considered.

If $G$ is profinite, the case of $N$ projective or the profinite completion of the fundamental group of a compact surface is considered.

Let $G$ be a finite group and suppose that $G = AB$, where $A$ and $B$ are abelian subgroups. By a theorem of Ito, the derived subgroup $G'$ is known to be abelian. If either of the subgroups $A$ or $B$ is cyclic, then more can be said. The paper shows, for example, that $G'{/}(G' \cap A)$ is isomorphic to a subgroup of $B$ in this case.

The concept of Yang–Baxter bases is useful in interpreting Young's constructions for the symmetric group. This concept is extended first to any Weyl group, and then to any Coxeter group.

A finite rewriting system is presented that does not satisfy the homotopical finiteness condition FDT, although it satisfies the homological finiteness condition FHT. This system is obtained from a group $G$ and a finitely generated subgroup $H$ of $G$ through a monoid extension that is almost an HNN extension. The FHT property of the extension is closely related to the ${\rm FP}_2$ property for the subgroup $H$, while the FDT property of the extension is related to the finite presentability of $H$. The example system separating the FDT property from the FHT property is then obtained by applying this construction to an example group.

On the symbolic space endowed with a metric given by a Gibbs measure, it is shown that, for any invariant probability measure $\mu$ other than the given Gibbs measure, the set of $\mu$-generical points satisfies a ‘zero-infinity law’ (in particular, its Hausdorff and packing measure are infinite). This extends a result of R. Kaufman on Besicovitch–Eggleston sets, and applies to level sets of Birkhoff averages and certain subsets of self-similar sets.

The integral closure and the Buchsbaum-Rim multiplicity are computed of a wide class of submodules of $\mathcal O_n^p$ through suitable Newton polyhedra. The result thus obtained is an extension to submodules of $\O^p$ of the works of Yoshinaga and Saia on the characterization of Newton non-degenerate functions and ideals, respectively.

The paper deals with the well posedness of a class of ordinary differential equations. The vector field depends on the solution to a scalar conservation law, whose flux function is assumed to have a single inflection point (from whence ‘nonconvex’ is derived). Filippov solutions to the ordinary differential equations are considered, and Hölder continuous dependence on the initial data is proved. The motivation for the problem is a model of traffic flow.

Topological properties of dynamical systems admitting a local product structure are studied. The results obtained are applied to hyperbolic systems on covers. The main theorem characterizes transitivity on solvable covers in terms of Frobenius elements of periodic orbits.

It is proved that a Banach space $X$ is a subspace of a weakly compactly generated Banach space if and only if, for every $\varepsilon\,{>}\,0$, $X$ can be covered by a countable collection of bounded closed convex symmetric sets where the weak$^*$ closure in $X^{**}$ of each of them lies within the distance $\varepsilon$ from $X$. A new short functional-analytic proof of the known result that a continuous image of an Eberlein compact is Eberlein is given as a corollary.

The asymptotic behaviour of entropy numbers of Trudinger–Strichartz embeddings of radial Besov spaces on ${\mathbb R}^n$ into exponential Orlicz spaces is calculated. Estimates of the entropy numbers as well as estimates of entropy numbers of Sobolev embeddings of radial Besov spaces are applied to spectral theory of certain pseudo-differential operators.

Let $(M_n)$ be a sequence of positive numbers satisfying $M_0\,{=}\,1$ and \[\displaystyle \frac{M_{n+m}}{M_n M_m}\,{\geq}\,{{n+m}\choose{m}} \] for all non-negative integers $m$, $n$. Let \[D([0,1], M)=\left\{f\,{\in}\,C^{\infty}([0,1]):\|f\|_{D}=\sum_{n=0}^{\infty} \frac{\|f^{(n)}\|_{\infty}}{M_n}\,{<}\,\infty\right\}.\] With pointwise addition and multiplication, $D([0,1],M)$ is a unital commutative semisimple Banach algebra. If $\lim_{n\to\infty} (n!/M_n)^{1/n}\,{=}\,0,$ then the maximal ideal space of the algebra is $[0,1]$, and every non-zero endomorphism $T$ has the form $Tf(x)\,{=}\,f(\phi(x))$ for some selfmap $\phi$ of the unit interval. The authors have previously shown for a wide class of $\phi$ mapping the unit interval to itself that if $\|\phi'\|_\infty\,{<}\,1$, then $\phi$ induces a compact endomorphism. The paper investigates the extent to which this condition is necessary, and the spectra of all compact endomorphisms of $D([0,1],M)$ are determined. Some of the authors' earlier results on general endomorphisms of $D([0,1],M)$ are simplified and strengthened.

Let K be the field of real or complex numbers. Let $(X \cong {\bf K}^{2n}, \omega)$ be a symplectic vector space and take $0 < k < n,N = ({2n \atop 2k})$. Let $L_1,\ldots,L_N \subset X$ be $2k$-dimensional linear subspaces which are in a sufficiently general position. It is shown that if $F : X \longrightarrow X$ is a linear automorphism which preserves the form $\omega^k$ on all subspaces $L_1,\ldots,L_N$, then $F$ is an $\epsilon_k$-symplectomorphism (that is, $F^*\omega = \epsilon_k\omega$, where $\epsilon_k^k = 1$). In particular, if ${\bf K} = \R$ and $k$ is odd then $F$ must be a symplectomorphism. The unitary version of this theorem is proved as well. It is also observed that the set ${\cal A}_{l,2r}$ of all $l$-dimensional linear subspaces on which the form $\omega$ has rank $\le 2r$ is linear in the Grassmannian $G(l,2n)$, that is, there is a linear subspace $L$ such that ${\cal A}_{l,2r} = L \cap G(l, 2n)$. In particular, the set ${\cal A}_{l,2r}$ can be computed effectively. Finally, the notion of symplectic volume is introduced and it is proved that it is another strong invariant.

Sun and Wilson defined the notion of infinite determinacy of a smooth function germ singular along a line, and related this notion to some good geometric properties of derived objects related to the given function germ. The paper extends their results to a wider class of smooth function with prescribed non-isolated singularities. For this purpose, it was necessary to study the behaviour of the function germ along a transverse direction of the given singular set, and to relate these properties to geometric properties of the function and derived objects, expressed in terms of relative Łojasiewicz conditions.

It is shown that for every non-negative integer $n$, there is a real $n$-dimensional family of minimal Lagrangian tori in $\mathbb{CP}^2$, and hence of special Lagrangian cones in $\mathbb{C}^3$ whose link is a torus. The proof utilises the fact that such tori arise from integrable systems, and can be described using algebro-geometric (spectral curve) data.