Openly generated Boolean algebras and the Fodor-type reection principle

Sakaé Fuchino, Assaf Rinot

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We prove that the Fodor-type Reection Principle (FRP) is equivalent to the assertion that any Boolean algebra is openly generated if and only if it is א2-projective. Previously it was known that this characterization of openly generated Boolean algebras follows from Axiom R. Since FRP is preserved by c.c.c. generic extension, we conclude in particular that this characterization is consistent with any set-theoretic assertion forcable by a c.c.c. poset starting from a model of FRP. A crucial step of the proof of the main result is to show that FRP implies Shelah's Strong Hypothesis (SSH). In particular, we show that FRP implies the Singular Cardinals Hypothesis (SCH). Extending a result of the second author, we also establish some new characterizations of SSH in terms of topological reection theorems.

Original languageEnglish
Pages (from-to)261-283
Number of pages23
JournalFundamenta Mathematicae
Issue number3
StatePublished - 2011
Externally publishedYes


  • Axiom R
  • Free Boolean algebra
  • Projective Boolean algebra
  • Shelah's Strong Hypothesis
  • Stationary reection


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