On Unconditionality and Higher-Order Schreier Unconditionality

Abstract

Let $X$ be a Banach space, $(e_n)_{n=1}^\infty$ be its basis, and $S_\alpha$ be a Schreier family of order alpha. We introduce Condition A which is a weaker version of the Continuum Hypothesis. Granted Condition A, we show that if the basis $(e_n)$ is $S_\alpha$-unconditional for every countable ordinal alpha, then it is unconditional.