Directed schemes of ideals and cardinal characteristics. I: The meager additive ideal

Abstract

We introduce the notion of directed scheme of ideals to characterize peculiar ideals on the reals, which comes from a formalization of the framework of Yorioka ideals for strong measure zero sets. We prove general theorems for directed schemes and propose a directed scheme (formula presented) for the ideal MA of meager-additive sets of reals. This directed scheme does not only helps us to understand more the combinatorics of MA and its cardinal characteristics, but provides us new characterizations of the additivity and cofinality numbers of the meager ideal of the reals. In addition, we display connections between the characteristics associated with MI and other classical characteristics. Furthermore, we demonstrate the consistency of cov(NA) < c and cof(MA) < non(SN). The first one answers a question raised by the authors in [14].