We obtain several characterizations of relatively weakly compact subsets in the predual of a JBW*-triple. As a consequence, we describe the relatively weakly compact subsets in the predual of a JBW*-algebra.

The theory of surfaces in Euclidean space can be naturally formulated in the more general context of Legendre surfaces into the space of contact elements. We address the question of deformability of Legendre surfaces with respect to the symmetry group of Lie sphere contact transformations from the point of view of the deformation theory of submanifolds in homogeneous spaces. Necessary and sufficient conditions are provided for a Legendre surface to admit non-trivial deformations, and the corresponding existence problem is discussed.

Given a real fan in a real space consisting of real convex polyhedral cones, we construct a complete real fan which contains the fan, by two completely different methods. The first one is purely combinatorial and a proof of a related version was sketched earlier by Ewald. The second one is based on Nagata’s method of imbedding an abstract variety into a complete variety. For the second method, we introduce the theory of Zariski-Riemann space of a fan

We generalize several results on the order of the isometry group of a compact manifold with negative Ricci curvature proved by Dai et al. under the assumption of bounded norm and an integral curvature bound. We also show that there exists a bound on the order of the isometry group depending on the weak norm of M.

A harmonic map of the Riemann sphere into the unit 4-dimensional sphere has area $4\pi\! d$ for some positive integer $d$, and it is well-known that the space of such maps may be given the structure of a complex algebraic variety of dimension $2d+4$. When $d$ less than or equal to 2, the subspace consisting of those maps which are linearly full is empty. We use the twistor fibration from complex projective 3-space to the 4-sphere to show that, if $d$ is equal to 3, 4 or 5, this subspace is a complex manifold.

This paper is concerned with the study of the Borel summability of divergent solutions for singularly perturbed inhomogeneous first-order linear ordinary differential equations which have a regularity at the origin. In order to assure the Borel summability of divergent solutions, global analytic continuation properties for coefficients are required despite the fact that the domain of the Borel sum is local.

We study the structure of the local cohomologymodules of the Fourier transform of A-hypergeometric systems. In particular, we are interested in local cohomology modules with respect to the orbit of a certain action on the toric variety determined by A. The purpose in this paper is to describe their structure by using a certain combinatorial object.

The Hankel transform transplantation operator is investigated by means of a suitably established local version of the Calderón-Zygmund operator theory. This approach produces weighted norm inequalities with weights more general than previously considered power weights. Moreover, it also allows to obtain weighted weak type $(1,1)$ inequalities, which seem to be new even in the unweighted setting. As a typical application of the transplantation, multiplier results in weighted $L^p$ spaces with general weights are obtained for the Hankel transform of any order $\alpha > -1$ greater than $-1$ by transplanting cosine transform multiplier results.