Let E be a real Banach space. If f: E→E is (Fréchet-) differentiable at every point of E, the derivative of f at x is denoted by f'(x), which is an element of the Banach algebra ℒ=ℒ(E) of all linear continuous mappings of E into itself with the usual upper bound norm, and, if we put , we have .

This paper introduces two new separation axioms, point paracompactness and point countable paracompactness, both somewhat weaker than regularity, and shows that they can replace regularity in several standard theorems about paracompact or absolutely H-closed or Lindelöf spaces. Thus we obtain sharpened versions of these theorems. We also show that under certain hypotheses the new properties are equivalent to regularity.

In the notation of Riordan ([5], p. 33), the Stirling numbers, s(n, k) and S(n, k), of the first and second kind respectively are defined by the relation where (x)n = x(x − 1) … (x − n + 1) is the factorial power function. They have been used by Jordan ([3], p. 184) to define the numbers C(m, k) and D(m, k), as linear combinations of s(n, k) and S(n, k) respectively, given by where and and where and D(m, O.

It is known that a divisor d>0 of the positive integer n is called unitary [3;§ 1] if dδ = n and (d, δ) = 1, where (d, δ) denotes the g.c.d. of d and δ. We write d¶. Let k be a fixed positive integer. A positve integer n is called k-free if n is not divisible by the kth power of any prime.

It is the aim of this paper to introduce a new concept relating various subgroups of the automorphism group of a graph to corresponding subgraphs. Throughout g will denote a (Michigan) graph on a vertex set V(¦V¦ =n) and Γ(g)=G will be the automorphism group of G considered as a permutation group on V.En, Cn, Dn and Sn are the identity, cyclic, dihedral, and symmetric groups acting on a set of size n, while Sp(q) is the permutation group of pq objects which is isomorphic to Sp but is q-fold in the sense that the objects are permuted q at a time [6]. H ≦ G means that H is a subgroup of G. Other group concepts can be found in Wielandt [7]. The graphs G1 ∪ G2, G1 + G2, G1 × G2, and G1[G2] along with their corresponding groups are as defined in, for example, Harary [4]. Finally we use Kn for the complete graph on n vertices.

Let ε, Λ, Λ*, ΛR stand for the set of non-negative integers, isols, isolic integers and regressive isols respectively, and let P(τ) be the ω-group of Gödel numbers of permutations of the set τ ε ε which move only finitely many elements of τ. The concept of an ω-group was studied by Hassett [5]. He proved in P12 of [5] that for an isolated set τ, the decomposition of P(τ) into conjugacy sets is a gc-decomposition if and only if τ is regressive. For the finite symmetric group on n elements, Sn it is known that the order of the conjugacy class is p(n), where p(n) is the partition function. The author shows in this paper, using a result of Barback [1], that if pΛ(T) is Nerode's canonical extension of p(n) to Λ and Req (τ) = T, then pΛ(T) = Req Cτ, where Cτ is the decomposition of P(τ) into conjugacy sets. The reader is assumed to be familiar with the contents of [2], [4] and [5].

In this note I follow the same notation adopted in [2]. Let Qk(x, n) denote the number of k-free integers ≦x which are prime to n. In [2], I proved the following: For o≦s>1/k uniformly, where σ*−s(n) is the sum of the reciprocals of the sth powers of the square-free divisor of n.

The Stokes-Beltrami equations, being applicable to many classes of physical problems, have for a long time received a great deal of attention from authors investigating their various aspects. One may cite, for example, Weinstein [1] and more recently Ranger [2] as just two of many research papers into this topic. Baecklund transformations have, in previous work, been applied to hodograph-type equations (Loowrner ], Power, Rogers and Onborn [4], Rogers [5, 6]) and reduction to appropriate canonical forms in elliptic, parabolic, and hyprebolic regimes has been achieved.

I can indicate the type of refinement mentioned in the title by referring to Kirchberger's theorem [4]. Its picturesque form in the plane is: if sheep and goats are grazing in a field and for every four animals there exists a line separating the sheep from the goats then there exists such a line for all the animals. The refinement is that the words ‘every four animals’ may be replaced by ‘every four animals including an arbitraily chosen animal’; this reduces the ‘Kirchberger number’ from four to, effectively, three.

This paper describes a one-step method besed upon the Lobatto four-point quadreture formula for the numerical integration of differential: y″(x) = f(x, y(x), y'(x)); y(x0)=y0, y'(x0)=y'0. The method has a local truncation error 0(h6) in y(x) and 0(h5) in y′(x). In the case of linear second-order differential equation, a stability criterion has been developed. Theoretical and computational comparisons of the new method existing method is discussed.

Let Σ∞n=0 an(sn=a0+…+an, n≧0) be a series of real or complex numbers. Denote by and two linear transforms T1 and T2 of {sn}. Estimates of the form for sequences {sn} satisfying where {dn} is a certain fixed linear transform of the sequence and depend on the transforms T1, T2 and {dn}, were considered for the first time by Hadwiger [2]. The smallest value of C satisfying (1.2) for all sequences {sn} satisfying (1.3) is known as the Tauberian constant associated with the pair of transforms T1, T2 and {dn}.

Even if in a decomposition of a group the Ai are completely indecomposable, there may be another decomposition with each Cj properly contained in some Ai a proper subgroup of B. The example of Bryce ([1], p. 636) may be modified, at the cost of having one Ai = B, so that I = J and Ci > Ai for all i. It is our object to study this relationship between decompositions of a group.

Following four important papers on Birkhoff interpolation by Turán and his associates ([2], [3], [4], [14]), Kis ([8], [19]) proved the following theorems.

It is well known that no rational number is approximable to order higher than 1. Roth [3] showed that an algebraic number is not approximable to order greater than 2. On the other hand it is easy to construct numbers, the Liouville numbers, which are approximable to any order (see [2], p. 162). We are led to the question, “Let Nn(α, β) denote the number of distinct rational points with denominators ≦ n contained in an interval (α, β). What is the behaviour of Nn(α, + 1/n) as α varies on the real line?” We shall prove that and that there are “compressions” and “rarefactions” of rational points on the real line.