Partition and almost disjoint properties of combinatorially rich sets in uncountable semigroups

Determine whether, for an infinite semigroup S of cardinality κ and a combinatorially rich subset A of S, the set A contains κ pairwise disjoint combinatorially rich subsets and, whenever κ contains λ almost disjoint subsets, contains λ almost disjoint combinatorially rich subsets.

Background

The paper proves that every combinatorially rich subset of (N, +) contains 2ω almost disjoint combinatorially rich subsets and can be partitioned into countably many pairwise disjoint combinatorially rich subsets. The authors explicitly leave open whether the corresponding cardinal-generalized conclusions hold in arbitrary infinite semigroups, particularly uncountable ones.

The unresolved issue has two parts: obtaining κ pairwise disjoint combinatorially rich subsets from a combinatorially rich set of a semigroup of size κ, and obtaining λ almost disjoint such subsets whenever the cardinal κ itself supports a family of λ almost disjoint subsets.

References

We do not know whether an analogous result of Theorem 3.2 holds in uncountable semigroups, so we close this section with this question. Question 3.3. If (S, +) is an infinite semigroup of size κ and A is combinatorially rich in S, then does A contain κ pairwise disjoint combinatorially rich subsets? Moreover, if κ contains λ almost disjoint subsets, then does A contain λ almost disjoint combinatorially rich subsets?

On partition and almost disjoint properties of combinatorial notions  (2501.11334 - Zhang, 20 Jan 2025) in Question 3.3, Section 3, p. 13