Resolvability and monotone normality

Abstract

A space $X$ is said to be $κ$-resolvable (resp. almost $κ$-resolvable) if it contains $κ$ dense sets that are pairwise disjoint (resp. almost disjoint over the ideal of nowhere dense subsets). $X$ is maximally resolvable iff it is $Δ(X)$-resolvable, where $Δ(X) = \min\{|G| : G \ne \emptyset {open}\}.$ We show that every crowded monotonically normal (in short: MN) space is $ω$-resolvable and almost $μ$-resolvable, where $μ= \min\{2^ω, ω_2 \}$. On the other hand, if $κ$ is a measurable cardinal then there is a MN space $X$ with $Δ(X) = κ$ such that no subspace of $X$ is $ω_1$-resolvable. Any MN space of cardinality $< \aleph_ω$ is maximally resolvable. But from a supercompact cardinal we obtain the consistency of the existence of a MN space $X$ with $|X| = Δ(X) = \aleph_ω$ such that no subspace of $X$ is $ω_2$-resolvable.