English

Team games, hypergraph spaces, and projective Boolean algebras

Logic 2022-03-02 v3 General Topology

Abstract

We modify the game Fuchino, Koppelberg, and Shelah used to characterize the κ\kappa-Freese-Nation property for a given Boolean algebra AA, replacing players I and II each with a team of nn players with limited information. We show that AA is tightly κ\kappa-filtered exactly when team II has a winning strategy for every finite team size. Case κ=0\kappa=\aleph_0 characterizes projective Boolean algebras and, hence, Dugundji spaces. In terms of the open-open game of Daniels, Kunen, and Zhou, this characterization is a team version of very I-favorable. We similarly characterize Cohen algebras in terms of a team version of I-favorability. If AA is the clopen algebra of the space of nn-uniform hypergraphs on κ+n\kappa^{+n} that avoid copies of [n+1]n[n+1]^n, then team II has a winning strategy for our modified FKS game for team size n1n-1 but not nn. For n3n\geq 3, this algebra also answers a question of Geschke when combined with a locally <κ{<}\kappa-sized characterization of tightly κ\kappa-filtered Boolean algebras that we prove. Case κ=0\kappa=\aleph_0 includes a locally finite characterization of projective Boolean algebras.

Keywords

Cite

@article{arxiv.1607.07944,
  title  = {Team games, hypergraph spaces, and projective Boolean algebras},
  author = {David Milovich},
  journal= {arXiv preprint arXiv:1607.07944},
  year   = {2022}
}

Comments

Greatly simplified main construction and extended results to Cohen and $\kappa$-tightly filtered algebras

R2 v1 2026-06-22T15:05:12.938Z