Relative cofinality of ideals

Abstract

We introduce a two-parameter modification of the cofinality invariant of ideals. This allows us to include the interaction of a pair of ideals in the study of base-like structures. We find the values (cardinal numbers or well-known cardinal invariants) of the invariant for pairs of some critical ideals on $\omega$. We also dichotomously divide pairs of known ideals on the real line based on whether their relative cofinality is trivial or uncountable. Finally, we also study the relative cofinality of maximal ideals.