In this paper, we discuss questions of the existence and calculation of periodic, steady flows over periodic streambeds. There are some surprises.

Problems such as this, of flows in running streams, are free-surface problems, and part of the difficulty is that the domain occupied by the fluid is not completely known a priori.

An ultrafilter completion is constructed for a nearness space. It is shown to preserve the Tl separation axiom. Characterizing conditions are given for it to be topological or for its topology to be compact. It is shown to have the simple extension topology and for a given Hausdorff space a compatible nearness structure is found for which its ultrafilter completion is homeomorphic to the Katetov H-closed extension.

A homeomorphism f of a space M is pointwise periodic if for each m ∈ M there exists an integer k such that fk(m) =m, where fk is the kth iterate of f. Montgomery proves [5] that if M is a connected topological manifold, then f is periodic; i.e., there exists an integer n such that fn = id. Noting this, Weaver [7] proves that if M is an orientable 2-manifold of class C1, U⊆M open and C ⊆ U a compact connected set and if g : U → M of class C1 is such that (i) g(C) = C and (ii) whenever the derivative of g at points x∈C has rank 2 it is orientation preserving, then f = g|c : C → C periodic implies that all but a finite number of points of C have as least period the period of f.

Let ∑ be a class of maps in a category An object I of is ∑-injective if is an epimorphism for all σ ∈ ∑. This paper is concerned with the question of finding “enough” S-injectives in a functorial way.

Let l and k be positive integers. Then for each integer n ≥ 1, define d(n; l, k) to be the number of (positive) divisors of n which lie in the arithmetic progression I mod k. Note that d(n;1,1) = d(n), the ordinary divisor function.

Nous considérons dans cette note une classe d′équations différentielles fonctionnelles linéaires dont les coefficients sont analytiques; des résultats sur l′ordre des solutions et leur comportement asymptotique seront obtenus.

Il s'agit d'une généralisation à des équations du deuxiéme ordre d'une propriété d'équations d'ordre un [2]: la démonstration du théoréme principal demeure valable dans ce dernier cas.

Let R∞ be the set of all the finite sequences of real numbers. The author shows that there are uncountably many distinct topologies on the set R∞, each of which coincides with the usual topology when restricted to an Rn. However, under each of these topologies, R∞ is always of the same homotopy type. A generalization to some other spaces is mentioned.

Hecke, [3], has shown for x a real Dirichlet character modulo q, the associated Dirichlet L-function L(s, x) has infinitely many zeroes on the line

Here, using a method of Polya, [5], we show that both the real and imaginary parts of a function associated to L(s, x) through the functional equation, have infinitely many zeroes on any line

It is shown that dentability of the unit ball of a conjugate Banach space X* does not imply smoothability of the unit ball of X, answering a question raised by Kemp. A property called strong smoothability is introduced and is shown to be dual to dentability. The results are used to provide new proofs of the facts that X is an Asplund space whenever it has an equivalent Fréchet differentiable norm, or whenever X* has the Radon-Nikodym Property.

Let L be a lattice, and let P and Q be partially ordered sets. We say that L is generated by P if there is an isotone mapping from P into L with its image generating L. P contains Q if there is a subset Q’ of P which, with the partial ordering inherited from P, gives an isomorphic copy of Q. For an integer n > 0, the lattice of partitions of an n-element set will be denoted by II(n); it is well-known that II(rc) is simple and complemented (cf. P. Crawley-R. P. Dilworth [1; p. 96]).

Arithmetic sums of the form

where f is an arithmetic function and [ ] is the greatest integer function frequently occur in various situations in the theory of numbers and have much of interest in their own right. Two instances appear in the well-known results.

Let S and T be locally compact topological semigroups and a semidirect product. Conditions are determined under which topological left amenability of S and T implies that of , and conversely. The results are used to show that for a large class of semigroups which are neither compact nor groups, various notions of topological left amenability coincide.

If is a von Neumann algebra that thas no nonzero finite discrete central projection, then there is no nontrivial compact derivation of into itself.

Let M be a differentiable manifold which admits the free action of a group Γ with compact quotient M’ = M/Γ. Suppose that the Γ action lifts to a Hermitian vector bundle E→M. If Γ leaves invariant a measure μ on M, then denote by L2(E) the completion of with respect to the inner product .

Following L. Fuchs [1], we define a valuated vector space to be a vector space V with a valuation from V to a totally ordered set Γ in which every nonempty subset has a supremum. It is assumed that Γ has a maximum element . A standard model for Γ is a closed initial segment of ordinals with the symbol ∞ adjoined.

We study the representations of an element of a free group as a commutator. For a given element g of a free group F, we are interested in the set of all pairs (x, y) of elements of F such that

(1)

where [x, y] = xyx-1 y-1. If g = 1, the problem is trivial. We assume henceforth that g ≠ 1.

In an article P. E. Himelwright and J. E. Williamson [3] proved a theorem on 1-factorability of Cartesian product of two graphs. With a very short proof we prove a more general theorem which immediately implies their theorem as a corollary. We will follow the notations and definitions of [1], [2] and [3].

We generalize a result of E. E. Floyd on unicoherent Peano continua with involution to unicoherent locally connected regular hereditarily Lindelöf spaces. The result has an application in the theory of connectivity functions.

Let X be a closed convex subset of a Banach space and let T: X → X be a nonexpansive mapping, i.e.

Let N and K be finite groups with K acting on N, and let G be the semidirect product NK It was shown by Zassenhaus that if (|N|, |K|) — 1 and either N or K is solvable (an assumption later rendered redundant by the Feit-Thompson theorem), then all complements of N in G are conjugate to K.