Let m ≥ 2 be a positive integer. Given a set E(ω) ⊆ ℕ we define $r_N^{\left(m\right)}\left(\omega \right)$ to be the number of ways to represent N ∈ ℤ as a combination of sums and differences of m distinct elements of E(ω). In this paper, we prove the existence of a “thick” set E(ω) and a positive constant K such that $r_N^{\left(m\right)}\left(\omega \right)<K$ for all N ∈ ℤ. This is a generalization of a known theorem by Erdős and Rényi. We also apply our results to harmonic analysis, where we prove the existence of certain thin sets.

Let $G$ be a locally compact group. We continue our work [A. Ghaffari: $\Gamma$-amenability of locally compact groups, Acta Math. Sinica, English Series, 26 (2010), 2313–2324] in the study of $\Gamma$-amenability of a locally compact group $G$ defined with respect to a closed subgroup $\Gamma$ of $G\times G$. In this paper, among other things, we introduce and study a closed subspace $A_{\Gamma }^p\left(G\right)$ of $L^{\infty }\left(\Gamma \right)$ and then characterize the $\Gamma$-amenability of $G$ using $A_{\Gamma }^p\left(G\right)$. Various necessary and sufficient conditions are found for a locally compact group to possess...

In the current work, a new notion of $n$-weak amenability of Banach algebras using homomorphisms, namely $(\varphi ,\psi )$-$n$-weak amenability is introduced. Among many other things, some relations between $(\varphi ,\psi )$-$n$-weak amenability of a Banach algebra $𝒜$ and $M_m\left(𝒜\right)$, the Banach algebra of $m\times m$ matrices with entries from $𝒜$, are studied. Also, the relation of this new concept of amenability of a Banach algebra and its unitization is investigated. As an example, it is shown that the group algebra $L^1\left(G\right)$ is ($\varphi ,\psi$)-$n$-weakly amenable for any...

This paper is part of a general program that was originally designed to study the Heat diffusion kernel on Lie groups.

In [3] I showed that there are Helson sets on the circle 𝕋 which are not of synthesis, by constructing a Helson set which was not of uniqueness and so automatically not of synthesis. In [2] Kaufman gave a substantially simpler construction of such a set; his construction is now standard. It is natural to ask whether there exist Helson sets which are of uniqueness but not of synthesis; this has circulated as an open question. The answer is "yes" and was also given in [3, pp. 87-92] but seems to...

We establish a Künneth formula for some chain complexes in the categories of Fréchet and Banach spaces. We consider a complex of Banach spaces and continuous boundary maps dₙ with closed ranges and prove that Hⁿ(’) ≅ Hₙ()’, where Hₙ()’ is the dual space of the homology group of and Hⁿ(’) is the cohomology group of the dual complex ’. A Künneth formula for chain complexes of nuclear Fréchet spaces and continuous boundary maps with closed ranges is also obtained. This enables us to describe explicitly...

Let $N$ be an $H$-type group and $S\simeq N\times {ℝ}^{+}$ be its harmonic extension. We study a left invariant Hardy–Littlewood maximal operator $M_{\rho }^{ℛ}$ on $S$, obtained by taking maximal averages with respect to the right Haar measure over left-translates of a family $ℛ$ of neighbourhoods of the identity. We prove that the maximal operator $M_{\rho }^{ℛ}$ is of weak type $(1,1)$.

The aim of the paper is to present some initial results about a possible generalization of moment sequences to a so-called q-calculus. A characterization of such a q-analogue in terms of appropriate positivity conditions is also investigated. Using the result due to Maserick and Szafraniec, we adapt a classical description of Hausdorff moment sequences in terms of positive definiteness and complete monotonicity to the q-situation. This makes a link between q-positive definiteness and q-complete...

We prove an $L^p$-boundedness result for a convolution operator with rough kernel supported on a hyperplane of a group of Heisenberg type.