A new axiom is proposed, the Ground Axiom, asserting that the universe is not a nontrivial set forcing extension of any inner model. The Ground Axiom is first-order expressible, and any model of zfc has a class forcing extension which satisfies it. The Ground Axiom is independent of many well-known set-theoretic assertions including the Generalized Continuum Hypothesis, the assertion v=hod that...

We study the concept of jointness for guessing principles, such as ♦κ and various Laver diamonds. A family of guessing sequences is joint if the elements of any given sequence of targets may be simultaneously guessed by the members of the family. We show that, while equivalent in the case of ♦κ, joint Laver diamonds are nontrivial new objects. We give equiconsistency results for most of the lar...

A question of Woodin asks if κ is strongly compact and GCH holds below κ, then must GCH hold everywhere? One variant of this question asks if κ is strongly compact and GCH fails at every regular cardinal δ < κ, then must GCH fail at some regular cardinal δ ≥ κ? Another variant asks if it is possible for GCH to fail at every limit cardinal less than or equal to a strongly compact cardinal κ. We ...

We construct a model where every increasing ω-sequence of regular cardinals carries a mutually stationary sequence which is not tightly stationary, and show that this property is preserved under a class of Prikry-type forcings. Along the way, we give examples in the Cohen and Prikry models of ω-sequences of regular cardinals for which there is a non-tightly stationary sequence of stationary sub...

This paper investigates the principles ta λ,δ, weakenings of λ which allow δ many clubs at each level but require them to agree on a tail-end. First, we prove that ta λ,<ω implies λ. Then, by forcing from a model with a measurable cardinal, we show that λ,2 does not imply ta λ,δ for regular λ, and ta δ+,δ does not imply δ+,<δ. With a supercompact cardinal the former result can be extended to si...

We prove that every tower of normal filters of height δ (δ supercompact) is precipitous assuming that each normal filter in the tower is the club filter restricted to a stationary set. We give an example to show that this assumption is necessary. We also prove that every normal filter can be generically extended to a well-founded V -ultrafilter (assuming large cardinals). In this paper we inves...

A general framework for proving relative consistency results with regard to supercompactness is developed. Within this framework we prove the relative consistency of the assertion that every set is ordinal definable with the statement asserting the existence of a supercompact cardinal. We also generalize Easton's theorem; the new element in our result is that our forcing conditions preserve sup...

In Part I of this series [A. Poveda, A. Rinot and D. Sinapova, Sigma-Prikry forcing I: The axioms, Canad. J. Math. 73(5) (2021) 1205–1238], we introduced a class notions which call [Formula: see text]-Prikry, showed that many the known Prikry-type center around singular cardinals countable cofinality are text]-Prikry. We given text]-Prikry poset text] text]-name for non-reflecting stationary se...