We study the torsion in the Mordell-Weil group of the Jacobian of the Fermat curve of exponent $p$ over the cyclotomic field obtained by adjoining a primitive $p$-th root of 1 to $Q$. We show that for all (except possibly one) proper subfields of this cyclotomic field, the torsion parts of the corresponding Mordell-Weil groups are elementary abelian $p$-groups.

Let $K$ be a number field, and let $X \subseteq P^{s-1}_K$ be a smooth complete intersection defined over $K$. In this paper, weak approximation is shown to hold for $X$ provided $s$ exceeds some function of the degree and codimension of $X$. This is a corollary of a more general result about the number of integral points on certain affine varieties in homogeneously expanding regions. This general result is established via a suitable adaptation of the Hardy-Littlewood Circle Method.

Explicit formulas for $K$-types of a $({\frak g}; K)$ module, such as Blattner's formula, are well known. However, the formulas are often too complex to make the $K$-type structure transparent. In this note we make use of some ideas of Vogan linking the ‘edges’ of the set of $K$-types to a certain restriction map from ${\frak u}$ to ${\frak u} \cap {\frak t}$ cohomology. It is hoped that such ideas will lead to tighter control of the set of $K$-types.

One-to-one correspondences are established between the set of all nondegenerate graded Jacobi operators of degree $-1$ defined on the graded algebra $\Omega(M)$ of differential forms on a smooth, oriented, Riemannian manifold $M$, the space of bundle isomorphisms $L{\A}TM{\to} TM$, and the space of nondegenerate derivations of degree $1$ having null square. Derivations with this property, and Jacobi structures of odd $\Bbb Z_2$-degree are also studied through the action of the automorphism group of $\Omega(M)$.

For a smooth projective variety $X$ of dimension $n$ in a projective space ${\bb P}^N$ defined over an algebraically closed field $k$, the Gauss map is a morphism from $X$ to the Grassmannian of $n$-plans in ${\bb P}^N$sending $x \in X$ to the embedded tangent space $T_xX \subset {\bb P}^N$. The purpose of this paper is to prove the generic injectivity of Gauss maps in positive characteristic for two cases; (1) weighted complete intersections of dimension $n \geqslant 3$ of general type; (2) surfaces or 3-folds with $\mu$-semistable tangent bundles; based on a criterion of Kaji by looking at the stability of Frobenius pull-backs of their tangent bundles. The first result implies that a conjecture of Kleiman-Piene is true in case $X$ is of general type of dimension $n \geqslant 3$. The second result is a generalization of the injectivity for curves.

In the thesis [Pe1] it was introduced, studied and applied a general theory of Weierstrass loci for vector bundles on a smooth curve. The results, proofs, background, examples and motivations of this thesis are contained in [Pe2]. We believe that this theory, at least in characteristic 0, is the ‘right’ one. The aim of this paper is to introduce and study an extension of [Pe1] to the case of higher dimensional varieties. At least two possible theories seem to be useful and natural; see the discussion just after Remark 1.1 and Section 4. We strongly prefer the ‘symmetric’ one (see Definition 1.5). In the first section we introduce the general theory and give the main general results. In the second section we study in details the case of $P^2$ for three reasons: it is nice; it shows how to use the general theory and what could be expected in more general situations and (last but not least) to convince the reader that it is technically easier and often more interesting to work in the ‘symmetric’ set up. Then in the third section we apply the method of Section 2 to a much more general situation (essentially, any variety $X$ as base of the vector bundle). In the fourth section we give the set up and start the analysis of specific examples of what happens near a specific point $P$ of the base variety $X$ (even when $X$ is singular at $P$). Here, except at the first step we are able to work only with the ‘symmetric’ definition.

Let $f:X\rightarrow Y$ be a morphism of noetherian schemes, generically smooth and equidimensional of dimension $d, \iota : X^{\prime} \rightarrow X$ a closed embedding such that $f \circ \iota : X^{\prime} \rightarrow Y$ is generically smooth and equidimensional of dimension $d^{\prime}$, and $X^{\prime}, X$ and $Y$ are excellent schemes without embedded components. We exhibit a concrete morphism{\rm Res}_{X^{\prime}/X}: {\rm det}\,{\cal N}_{X^{\prime}/X} \otimes_{{\cal O}_{X^{\prime}}} \iota^* \omega^d_{X/Y} \rightarrow \omega^{d^{\prime}}_{X^{\prime}/Y},