It is shown that any sheaf of R˜-modules, all of whose stalks are injective, is necessarily a flabby sheaf. This generalizes the result or Grothendieck that the sheaf M˜ determined by an injective module M over a commutative noetherian ring with 1 is flabby.

This paper discusses solutions to the differential equation

which governs the height

of the non-dimensional water level inside a conventional tide-well when the corresponding height of the sea-level outside is X(τ). A perturbation solution correct to O(β4), for small β, for the particular case X = sinτ described previously has been extended to O(β6) for any function X(τ) differentiable at least three times. Two special cases, where X(τ) is a single sinusoid and the sum of two sinusoids, are treated in detail.

A graph Γ is called symmetric if its automorphism group is transitive on its vertices and edges. Let p be an odd prime, Z(p) the field of integers modulo p, and Z*(p) = (a ∈ Z(p) | a ≠ 0}, the multiplicative subgroup of Z(p). This paper gives a simple proof of the equivalence of two statements:

(1) Γ is a symmetric graph with p vertices, each having degree n ≥ 1;

(2) the integer n is an even divisor of p − 1 and Γ is isomorphic to the graph whose vertices are the elements of Z(p) and whose edges are the pairs {a, a+h} where a ∈ Z(p) and h ∈ H, the unique subgroup of Z*(p) of order n.

In addition, the automorphism group of Γ is determined.

The following conditions for a group G are investigated:

(i) maximal class n subgroups are normal,

(ii) normal closures of elements have nilpotency class n at most,

(iii) normal closures are n–Engel groups,

(iv) G is an (n+1 )-Engel group.

Each of these conditions is a consequence of the preceding one. The second author has shown previously that all conditions are equivalent for n = 1. Here the question is settled for n = 2 as follows: conditions (ii), (iii) and (iv) are equivalent. The class of groups defined by (i) is not closed under homomorphisms, and hence (i) does not follow from the other conditions.

We give a construction for Hadamard arrays and exhibit the arrays of orders 4t, t ∈ {1, 3, 5, 7, …, 19}. This gives seventeen new Hadamard matrices of order less than 4000.

Using the characterization of the free inverse semigroup F on a set X, given by Scheiblich, a necessary and sufficient condition is found for a subset K of an inverse semigroup S to be a set of free generators for the inverse sub semigroup of S generated by K. It is then shown that any non-idempotent element of F generates the free inverse semigroup on one generator and that if |X| > 2 then F contains the free inverse semigroup on a countable number of generators. In addition, it is shown that if |X| = 1 then F does not contain the free inverse semigroup on two generators.

The dynamic response of a prestressed incompressible Mooney material is studied by investigating plane wave propagation and the response of the material to impulsive lines of force. The choice of an initial deformation which is axially symmetric gives a particularly simple form for the secular equation for the plane wavefront velocities. The speeds of propagation and the amplitudes of the two permissible transverse waves are found and necessary and sufficient conditions for there to exist two real wave speeds in all directions are established. The simple form of the secular equation enables the response of the material to concentrated disturbances to be readily solved using Fourier transforms. The motions caused by a line of impulsive forces is examined in some detail.

We give the representation formula of a function in a disc in terms of its arithmetic means on the boundary. We also give applications of this formula to the solutions of some elementary differential equations with prescribed means of boundary or initial data.

It is shown that if G is an arbitrary regular product of its subgroups Aλ, ∈ ϵ I, then the multiplicator, M(G), is the director product of the M(Aλ) together with a certain other group. This extends a calculation of M(A1 × A2) due to Schur. As an application, we find the multiplicator of a vertai wreath product A wrVB where A is abelian. A representing group for a finite regular product is also constructed.

Let (X, T) be a topological space (we assume T1. throughout) where every point is a limit point. The purpose of this note is to present an internal construction of a maximal perfect topology on (X, T). The existence of a maximal connected Hausdorff space has not been demonstrated. However, this construction of a maximal perfect topology is useful in constructing connected Hausdorff spaces which cannot be embedded in a maximal connected Hausdorff space.

It is shown that, in a variety which does not contain all metabelian groups and is contained in a product of (finitely many) varieties each of which is soluble or locally finite, every group is an extension of a group of finite exponent by a nilpotent group by a group of finite exponent.

The question has been raised [R.J. Loy, Bull. Austral. Math. Soc. 5 (1970), 253–260] as to whether the existence of a bounded (left) approximate identity in the tensor product A ⊗αB of Banach algebras A and B (for a a crossnorm on A ⊗ B ) implies the existence of a bounded (left) approximate identity in A and B. This is known [David A. Robbins, Bull. Austral. Math. Soc. 6 (1972), 443–445] to be the case for α equal to the greatest crossnorm. This paper answers the general question affirmatively.