This article contains a fundamental error in the limit case of the proof of properness of the relevant forcing notion. More specifically, the main problems in this proof stem from the fact that, in the construction in this paper, there is a priori no way to ensure isomorphism, at the level of the predicates involved, of the models obtained via the relevant copying. We renounce our original claim of having solved the problem of forcing Measuring together with 2 0 > 2 .

Abstract I construct, in ZFC, a forcing notion that collapses $\aleph _3 $ and preserves all other cardinals. The existence of such a forcing answers a question of Uri Abraham from 1983.

We study the spectrum of forcing notions between the iterations of σ-closed followed by ccc forcings and the proper forcings. This includes the hierarchy of α-proper forcings for indecomposable countable ordinals α, the Axiom A forcings and forcings completely embeddable into an iteration of a σ-closed followed by a ccc forcing. For the latter class, we present an equivalent characterization in terms of Baumgartnerʼs Axiom A. This resolves a conjecture of Baumgartner from the 1980s. We also study the bounded forcing axioms for the hierarchy of α-proper forcings. Following ideas of Shelah we separate them for distinct countable indecomposable ordinals.

Abstract Assuming 2ℵ0 = ℵ1 and 2ℵ1 = ℵ2, we build a partial order that forces the existence of a well-order of H(ω2) lightface definable over ⟨H(ω1), ∈⟩ and that preserves cardinal exponentiation and cofinalities.

Abstract After presenting a general setting in which to look at forcing axioms, we give a hierarchy of generalized bounded forcing axioms that correspond level by level, in consistency strength, with the members of a natural hierarchy of large cardinals below a Mahlo. We give a general construction of models of generalized bounded forcing axioms. Then we consider the bounded forcing axiom for a class of partially ordered sets Γ1 such that, letting Γ0 be the class of all stationary-set-preserving partially ordered sets, one can prove the following: (a) Γ0 ⊆ Γ1, (b) Γ0 = Γ1 if and only if NSω1 is ℵ1-dense. (c) If P ∉ Γ1, then BFA({P}) fails. We call the bounded forcing axiom for Γ1Maximal Bounded Forcing Axiom (MBFA). Finally we prove MBFA consistent relative to the consistency of an inaccessible Σ2-correct cardinal which is a limit of strongly compact cardinals.

Abstract We prove that a form of the Erdӧs property (consistent with V = L[Hω2] and strictly weaker than the Weak Chang's Conjecture at ω1), together with Bounded Martin's Maximum implies that Woodin's principle ψAC holds, and therefore . We also prove that ψAC implies that every function f: ω1 → ω1 is bounded by some canonical function on a club and use this to produce a model of the Bounded Semiproper Forcing Axiom in which Bounded Martin's Maximum fails.