Abstract We produce, relative to a backslash textsf upper Z upper F upper C $\textsf {ZFC}$ \textsf Z F C model with a supercompact cardinal, a backslash textsf upper Z upper F upper C $\textsf {ZFC}$ \textsf Z F C model of the Proper Forcing Axiom in which the nonstationary ideal on omega 1 $\omega _1$ ω 1 is upper Pi 1 $\Pi _1$ Π 1 -definable in a parameter from upper H Subscript normal first transfinite cardinal 2 $H_{\aleph _2}$ H ℵ 2 .

Abstract We develop technology for investigation of natural forcing extensions of the model $L\left( \mathbb{R} \right)$ which satisfy such statements as “there is an ultrafilter” or “there is a total selector for the Vitali equivalence relation”. The technology reduces many questions about ZF implications between consequences of the Axiom of Choice to natural ZFC forcing problems.

Abstract Theorem. Suppose that k = (K, $$\prec_k$$ ) is an ℵ0-presentable abstract elementary class with Löwenheim–Skolem number ℵ0, satisfying the joint embedding and amalgamation properties in ℵ0. If K has only countably many models in ℵ1, then all are small. If, in addition, k is almost Galois ω-stable then k is Galois ω-stable. Suppose that k = (K, $$\prec_k$$ ) is an ℵ0-presented almost Galois ω-stable AEC satisfying amalgamation for countable models, and having a model of cardinality ℵ1. The assertion that K is ℵ1-categorical is then absolute.

Abstract We shall show the consistency of CH+⌝(+) and CH+(+)+there are no club guessing sequences on ω1. We shall also prove that ◊+ does not imply the existence of a strong club guessing sequence on ω1.

Abstract In his book on ℙmax [7], Woodin presents a collection of partial orders whose extensions satisfy strong club guessing principles on ω1. In this paper we employ one of the techniques from this book to produce ℙmax variations which separate various club guessing principles. The principle (+) and its variants are weak guessing principles which were first considered by the second author [4] while studying games of length ω1. It was shown in [1] that the Continuum Hypothesis does not imply (+) and that (+) does not imply the existence of a club guessing sequence ω1. In this paper we give an alternate proof of the second of these results, using Woodin's ℙmax technology, showing that a strengthening of (+) does not imply a weakening of club guessing known as the Interval Hitting Principle. The main technique in this paper, in addition to the standard ℙmax machinery, is the use of condensation principles to build suitable iterations.

Abstract We present Woodin's proof that if there exists a measurable Woodin cardinal δ then there is a forcing extension satisfying all sentences ϕ such that CH + ϕ holds in a forcing extension of V by a partial order in Vδ. We also use some of the techniques from this proof to show that if there exists a stationary limit of stationary limits of Woodin cardinals, then in a homogeneous forcing extension there is an elementary embedding j: V → M with critical point such that M is countably closed in the forcing extension.

Abstract We isolate a forcing which increases the value of while preserving ω1 under the assumption that there is a precipitous ideal on ω1 and a measurable cardinal.

Abstract The forcing construction ℙmax, invented by W. Hugh Woodin, produces a model whose collection of subsets of ω1 is in some sense maximal. In this paper we study the Boolean algebra induced by the nonstationary ideal on ω1 in this model. Among other things we show that the induced quotient does not have a simply definable form. We also prove several results about saturation properties of the ideal in this extension.

Abstract If M is a countable transitive model of , then for every real x there is a unique shortest iteration j: M → N with x ∈ N, or none at all.

Abstract We present a variety of (ω, ∞)-distributive forcings which when applied to models of Martin's Maximum separate certain well known reflection principles. In particular, we do this for the reflection principles SR, SRα (α ≤ ω1), and SRP.

Abstract We present a variation of the forcing as presented in Woodin [4], Our forcing is a ℙmax-style construction where each model condition selects one Souslin tree. In the extension there is a Souslin tree TG which is the direct limit of the selected Souslin trees in the models of the generic. In some sense, the generic extension is a maximal model of "there exists a minimal Souslin tree,” with TG being this minimal tree. In particular, in the extension this Souslin tree has the property that forcing with it gives a model of Souslin's Hypothesis.