Macphail's Theorem revisited
Abstract
In 1947, M. S. Macphail constructed a series in that converges unconditionally but does not converge absolutely. According to the literature, this result helped Dvoretzky and Rogers to finally answer a long standing problem of Banach Space Theory, by showing that in all infinite-dimensional Banach spaces, there exists an unconditionally summable sequence that fails to be absolutely summable. More precisely, the Dvoretzky--Rogers Theorem asserts that in every infinite-dimensional Banach space there exists an unconditionally convergent series such that for all Their proof is non-constructive and Macphail's result for provides a constructive proof just for In this note we revisit Machphail's paper and present two alternative constructions that work for all
Keywords
Cite
@article{arxiv.2006.07626,
title = {Macphail's Theorem revisited},
author = {Daniel Pellegrino and Janiely Silva},
journal= {arXiv preprint arXiv:2006.07626},
year = {2020}
}