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Published online by Cambridge University Press: 07 August 2025
Denote by $\mathcal {NA}$ and
$\mathcal {MA}$ the ideals of null-additive and meager-additive subsets of
$2^{\omega }$, respectively. We prove in ZFC that
$\mathrm {add}(\mathcal {NA})=\mathrm {non}(\mathcal {NA})$ and introduce a new (Polish) relational system to reformulate Bartoszyński’s and Judah’s characterization of the uniformity of
$\mathcal {MA}$, which is helpful to understand the combinatorics of
$\mathcal {MA}$ and to prove consistency results. As for the latter, we prove that
$\mathrm {cov}(\mathcal {MA})<\mathfrak {c}$ (even
$\mathrm {cov}(\mathcal {MA})<\mathrm {non}(\mathcal {N})$) is consistent with ZFC, as well as several constellations of Cichoń’s diagram with
$\mathrm {non}(\mathcal {NA})$,
$\mathrm {non}(\mathcal {MA}),$ and
$\mathrm {add}(\mathcal {SN})$, which include
$\mathrm {non}(\mathcal {NA})<\mathfrak {b}< \mathrm {non}(\mathcal {MA})$ and
$\mathfrak {b}< \mathrm {add}(\mathcal {SN})<\mathrm {cov}(\mathcal {M})<\mathfrak {d}=\mathfrak {c}$.