If G is a unipotent group of n×n matrices over a division ring of characteristic 0 or prime p greater than (n- 1) (n-[n/2]) where [n/2] is the greatest integer less than or equal to n/2, then it is proved that G can be simultaneously triangularized.

This note concerns elements (called trivectors) of the third Grassmann product of a complex vector space U. Usually there are many ways to write a given trivector as the sum of simple or decomposable trivectors, and it is an interesting problem to find those representations which contain the smallest possible number of decomposables. This number we shall call the length of the trivector. Let N(n) denote the length of the longest trivector in ∧3U where U has dimension n. In this note we give upper bounds for N(n) when n ≤ 8.

A ray in Euclidean n-dimensional space Rn is a set of the form {a + λb: λ≥ 0 } where a and b are fixed points in Rn and b≠0.

The subject of this paper is a Helly type theorem for convex sets in Rn.

If is a finite family of at least 2n convex sets in Rn and if theintersection of any 2n members of contains a ray then containsa ray.

A form P of degree r is a homogeneous polynomial in k[Yi, …, Yn] on kn, k a field; Yi are the coordinate functions on kn. Let V(n, r) denote the k-vector space of forms of degree r. Mn(k) = Endk(kn) has canonical Lie algebra structure with [A, B] = AB-BA and it acts as a k-Lie Algebra of kderivations of degree 0 on k[Yi, …, Yn] defined by setting D(A)Y= Yo(-A) for A∈Endk(kn), Y∈V(n,l) = Homk(kn, k) and extending as a k-derivation. Define the orthogonal Lie Algebra, LO(P), of P by LO(P) =

Throughout this note, let R be a (commutative integral) domain with quotient field K. A domain S satisfying R ⊆ S ⊆ K is called an overring of R, and by dimension of a ring we mean Krull dimension. Recall [1] that a commutative ring is said to be coherent if each finitely generated ideal is finitely presented.

In [2], as a corollary of a more general theorem, Davis showed that if each overring of a domain R is Noetherian, then the dimension of R is at most 1. (This corollary is the converse of a version of the Krull-Akizuki Theorem [5, Theorem 93], and can also be proved directly by using the existence of valuation rings dominating finite chains of prime ideals [4, Corollary 16.6].) It is our purpose to prove that if R is Noetherian and each overring of R is coherent, then the dimension of £ is at most 1. We shall also indicate some related questions and examples.

An example of the type described in the title is given.

Let k be a field. Two field extensions E, F of k are said to have a product- in the category of field extensions of k (see e.g. [1, p. 30]) if and only if there exist a field extension P of k and two k -isomorphisms P→ E, P→ F satisfying the following universal property. For any field extension K of k and any pair of k-isomorphisms K→E, K→F, there exists a unique k-isomorphism K→P such that the diagrams below commute.

Self-complementary digraphs, and oriented type of these were counted by Read [4] and Sridharan [5] respectively. In [3] Palmer obtained an asymptotic formula for the number of self-complementary digraphs following a method of Oberschelp [2]. An asymptotic formula for the number of self-complementary oriented graphs is given here. We refer to [1] for definitions and details not mentioned here.