It is shown that it is possible to extend α Hölder maps from subsets of Lp to Lq (1 < p, q ≤ 2) isometrically if and only if α≤p/q*, and isomorphically if and only if α≤p/2. It is also proved that the set of αs which allow an isomorphic extension for α Hölder maps from subsets of X to Y is monotone when Y is a dual Banach space. Finally, the isometric and isomorphic extension problems for Hölder functions between Lp and Lq is studied for general p, q ≥ 1, and a question posed by K. Ball is solved by showing that it is not true that all Lipschitz maps from subsets of Hilbert space into normed spaces extend to the whole of Hilbert space.

It is shown that, if h and k are harmonic in ℝ2 and there exists a positive constant c so that

in ℝ2, where h+ = max {h, 0}, then it need not follow that h - k is identically a constant. The necessary counterexample is obtained by applying Arakelyan's theorem on approximation by an entire function in certain regions in ℝ2.

Montgomery and Vaughan [12] have shown that the exceptional set in Goldbach's problem

satisfies

for some Δ>0. Li [10,11] has shown that we may take Δ = 0·079 and Δ = 0·086. If the Riemann Hypothesis is true for all Dirichlet L-functions then (1) holds for any Δ<½. This is a classical result due to Hardy and Littlewood [7].

By a recent result, the number of common tangent lines to four unit balls in ℝ3 is bounded by 12 unless the four centres are collinear. In the present paper, this result is complemented by showing that indeed every number of tangents k ∈ {0, …, 12} can be established in real space. The constructions combine geometric and algebraic aspects of the tangent problem.

A major result of D. B. McAlister is that every inverse semigroup is an idempotent separating morphic image of an E-unitary inverse semigroup. The result has been generalized by various authors (including Szendrei, Takizawa, Trotter, Fountain, Almeida, Pin, Weil) to any semigroup of the following types: orthodox, regular, ii-dense with commuting idempotents, E-dense with idempotents forming a subsemigroup, and is-dense. In each case, a semigroup is a morphic image of a semigroup in which the weakly self conjugate core is unitary and separated by the homomorphism. In the present paper, for any variety H of groups and any E-dense semigroup S, the concept of an “H-verbal subsemigroup” of S is introduced which is intimately connected with the least H-congruence on S. What is more, this construction provides a short and easy access to covering results of the aforementioned kind. Moreover, the results are generalized, in that covers over arbitrary group varieties are constructed for any E-dense semigroup. If the given semigroup enjoys a “regularity condition” such as being eventually regular, group bound, or regular, then so does the cover.

It is shown that, for any lattice polytope P⊂ℝd the set int (P)∩lℤd (provided that it is non-empty) contains a point whose coefficient of asymmetry with respect to P is at most 8d · (8l+7)22d+1. If, moreover, P is a simplex, then this bound can be improved to 8 · (8l+7 )2d+1. As an application, new upper bounds on the volume of a lattice polytope are deduced, given its dimension and the number of sublattice points in its interior.

This paper is concerned with convex bodies in n-dimensional lp, spaces, where each body is accessible only by a weak separation or optimization oracle. It studies the asymptotic relative accuracy, as n→∞, of polynomial-time approximation algorithms for the diameter, width, circumradius, and inradius of a body K, and also for the maximum of the norm over K.

A partition of the positive integer n into distinct parts is a decreasing sequence of positive integers whose sum is n, and the number of such partitions is denoted by Q(n). If we adopt the convention that Q(0) = 1, then we have the generating function

Improved upper and lower bounds of the counting functions of the conceivable additive decomposition sets of the set of primes are established. Suppose that where, ℝ′ differs from the set of primes in finitely many elements only and .

It is shown that the counting functions A(x) of ℐ and B(x) of ℬ for sufficiently large x, satisfy

The centroid body. Recall that the support function of a compact convex set K is denned to be hK(u) = maxxΣk: {<u, x>}. The support function hK is positive homogeneous and convex, and any function with these properties is the support function of some compact convex set (see the illuminating paper of Berger [2], or the classic [5] by Bonnesen and Fenchel).

The purpose of this paper is to show how a sieve method which has had many applications to problems involving rational primes can be modified to derive new results on Gaussian primes (or, more generally, prime ideals in algebraic number fields). One consequence of our main theorem (Theorem 2 below) is the following result on rational primes.

A tiling of a convex m-gon by a finite number r of convex n-gons is said to be of type <m, n, r>. The Main Theorem of this paper gives necessary and sufficient conditions on m, n and r for a tiling of type <m, n, r> to exist.

Let (bn) be a sequence of integers, obtained by traversing the rows of Pascal's triangle, as follows: start from the element at the top of the triangle, and at each stage continue from the current element to one of the elements at the next row, either the one immediately to the left of the current element or the one immediately to its right. Consider the distribution of the sequence (bnα) modulo 1 for an irrational α. The main results show that this sequence “often” fails to be uniformly distributed modulo 1, and provide answers to some questions raised by Adams and Petersen.

A subsemigroup S of a semigroup Q is an order in Q if, for every q ∈ Q, there exist a, b, c, d ∈ S such that q = a−1b = cd−1 where a and d are contained in (maximal) subgroups of Q and a−1 and d−1 are their inverses in these subgroups. A semigroup which is a union of its subgroups is completely regular.