Vol 11, No 2 (2019)

For Hausdorff operator of general type defined on p-adic linear space \(\mathbb{Q}_p^n\), we give sufficient conditions of its boundedness in weighted Lebesgue and grand Lebesgue spaces. Sharpness of some these conditions is also established.

The theory of X-normed spaces over non-Archimedean valued fields with valuations of higher rank was introduced by H. Ochsenius and W. H. Schikhof in [9] and further developed in [10–12, 16, 17] and [13]. In order to obtain results like the Open Mapping Theorem, the Closed Graph Theorem and the Uniform Boundedness Theorem, H. Ochsenius and W. H. Schikhof used 1st countability conditions in the value group of the based field. In this article the author develops a new tool to work with transfinite induction simplifying the techniques employed in X-normed spaces, thus accomplishing a Generalized Baire Category Theorem that allows the proof of an Open Mapping Theorem for X-normed spaces without restrictions on the value group of the based field. Additionally, some contributions to the theory of X-normed spaces are presented regarding quotient spaces.

Some problems in the theory of approximation of complex-valued functions on locally compact Vilenkin groups in the metric of L^p, 1 ≤ p ≤ ∞, by functions with bounded spectrum, are investigated. A description of certain function spaces in terms of the best approximations are obtained and some imbedding theorems are proved.