Generalized Martin’s Axiom and Souslin’s hypothesis for higher cardinals

We consider different generalizations of Martin’s Axiom to higher cardinals. For ℵ₁, assuming CH+2^ℵ ₁>ℵ₂+□_ℵ1 we show that a generalized Martin’s Axiom considered by Baumgartner settles the ℵ₂ Souslin Hypothesis ... the wrong way. We further show that, assuming CH+2^ℵ ₁>ℵ₂, a strengthening of this axiom implies □_{ℵ 1}. Finally, we show that a seemingly innocuous further strengthening is inconsistent with CH+2^ℵ ₁>ℵ₂. This author thanks the US-Israel Binational Science Foundation for partial support of this research.     

Consistency results on infinite graphs

Consistently there exist ℵ₂-chromatic graphs with no ℵ₁-chromatic subgraphs. The statement that every uncountably chromatic graph of size ℵ₁ contains an uncountably chromaticω-connected subgraph is consistent and independent. It is consistent that there is an uncountably chromatic graph of size ℵ_{ω 1} in which every subgraph with size less than ℵ_{ω 1} is countably chromatic. Partially supported by Hungarian Science Research Fund Nu. 1805.     

Categoricity,amalgamation, and tameness

Theorem: For each 2 ≤ k < ω there is an -sentence ϕ_k such that (1) ϕ_k is categorical in μ if μ≤ℵ_k−2; (2) ϕ_k is not ℵ_k−2-Galois stable (3) ϕ_k is not categorical in any μ with μ>ℵ_k−2; (4) ϕ_k has the disjoint amalgamation property (5) For k > 2 (a) ϕ_k is (ℵ₀, ℵ_k−3)-tame; indeed, syntactic first-order types determine Galois types over models of cardinality at most ℵ_k−3; (b) ϕ_k is ℵ_m-Galois stable for m ≤ k − 3 (c) ϕ_k is not (ℵ_k−3, ℵ_k−2). The first author is partially supported by NSF grant DMS-0500841.     

Characteristic features of the dynamics of the Ginzburg-Landau equation in a plane domain

We study the boundary value problem w_t=ℵ₀Δw+ℵ₁w-ℵ₂w|w|²,w|∂Ω₀=0 in the domain Ω₀={(x,y):0 ≤ x ≤ l₁,0 ≤ y ≤ l₂}. Here, w is a complex-valued function, Δ is the laplace operator, and ℵ_j, j=0,1,2, are complex constants withRe ℵ_j > 0. We show that under a rather general choice of the parameters l₁ and l₂, the number of stable invariant tori in the problem, as well as their dimensions, grows infinitely asRe ℵ₀ → 0 andRe ℵ₀ → 0. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 125, No. 2, pp. 205–220, November, 2000.     

On a Chang conjecture

We use the core model for the one strong cardinal to show that the Chang Conjecture (ℵ _n+2, ℵ _n+1) ⇒ (ℵ _n+1, ℵ _n ) together with 2^ℵ _{n − 1} = ℵ _n implies, for 1<n<ω, the existence of an inner model with a strong cardinal. An essential step of our proof is an application of the Gitik Game which also admits a presentation.     

Multi-dimensionality

We prove that ifT is stable, not multi-dimensional theory, then there is an infinite indiscernible set orthogonal to the empty set. This completes the proof that if ℵ_α=ℵ _•T• ^α >ℵ≥_Kr(T), thenT has ≥2^•α−β• non-isomorphic ℵ_β models of cardinality ℵ_α. Originally written November 5, 1988. Publication 429. Partially supported by the Israel-United States Binational Science Foundation; I thank Alice Leonhardt for the beautiful typing.     

Uniformization and the diversity of Whitehead groups

Techniques of uniformization are used to prove that it is not consistent that the Whitehead groups of cardinality ℵ₁ are exactly the strongly ℵ₁-free groups. Some consequences of the assumption that every strongly ℵ₁-free group of cardinality ℵ₁ is Whitehead are derived. Other results about uniformization are also proved. Research partially supported by NSERC grant #9848. Research partially supported by the BSF. The authors thank Rutgers University for its support. Publication #441.     

On the number of homogeneous models of a given power

It is shown that, For each complete theoryT, the nomberh _T(m) of homogeneous models ofT of powerm is a non-increasing function of uncountabel cardinalsm Moreover, ifh _T(ℵ₀)≦ℵ₀, then the functionh _T is also non-increasing ℵ₀ to ℵ₁. This work was supported in part by NSF contracts GP 4257 and GP5913.     

Violating the singular cardinals hypothesis without large cardinals

We extend a transitive model V of ZFC+GCH cardinal preservingly to a model N of ZF + “GCH holds below ℵ _ω ” + “there is a surjection from the power set of ℵ _ω onto λ”, where λ is an arbitrarily high fixed cardinal in V. The construction can be described as follows: add ℵ _n +1 many Cohen subsets of ℵ _n+1 for every n < ω, and adjoin λ many subsets of ℵ _ω which are unions of ω-sequences of those Cohen subsets; then let N be a choiceless submodel generated by equivalence classes of the λ subsets of ℵ _ω modulo an appropriate equivalence relation.     

On a poset algebra which is hereditarily but not canonically well generated

LetB be a superatomic Boolean algebra.B is well generated, if it has a well founded sublatticeL such thatL generatesB. The free product of Boolean algebrasB andC is denoted byB *C. IfC is a chain thenB(C) denotes the interval algebra overC. Theorem 1: (a)Every Boolean subalgebra of B(ℵ₁) *B(ℵ₀)is well-generated. (b)B(ℵ₁) *B(ℵ₁)contains a non well-generated Boolean subalgebra. Canonical well-generatedness is defined in the introduction. Recall thatB(ℵ₁) *B(ℵ₀) is canonically well-generated, and thus well-generated. We prove the following result. Theorem 2:B(ℵ₁) *B(ℵ₀)contains a non canonically well generated Boolean subalgebra. In contrast with Theorem 1(b), we have the following result. Theorem 3:Let A ={ɑ:α<ℵ₁}⊆℘(w)be a strictly increasing sequence in the relation of almost containment. Let B be the subalgebra of ℘(w)generated by {{n}:n∈ℵ₀}∪A.Then B is superatomic, and B is not embeddable in a well-generated algebra.     

Large continuum,oracles

Our main theorem is about iterated forcing for making the continuum larger than ℵ₂. We present a generalization of [2] which deal with oracles for random, (also for other cases and generalities), by replacing ℵ₁,ℵ₂ by λ, λ ⁺ (starting with λ = λ ^<λ > ℵ₁). Well, we demand absolute c.c.c. So we get, e.g. the continuum is λ ⁺ but we can get cov(meagre) = λ and we give some applications. As in non-Cohen oracles [2], it is a “partial” countable support iteration but it is c.c.c.     

Determinacy implies that ℵ2 is supercompact

Assuming the axiom of determinacy, ℵ₁ and ℵ₂ areδ-supercompact, whereδ is a fairly large cardinal which will be defined below.     

Some ℵ0-bounded subsets of stone-čech compactifications

We characterize the maximalm-bounded extension of an arbitrary completely regular Hausdorff spaceX. The other principal results are:Theorem. LetX be a locally compact, σ-compact non-compact space with no more than 2^ℵ0 zero-sets. Then assuming the continuum hypothesis,βX − X can be written as the union of 2^2ℵ0 pairwise disjoint, dense ℵ₀-bounded subspaces.Theorem. LetX be a locally compact, σ-compact metric space without isolated points. Then both the set of remote points ofβX and the complement of this set inβX −X are ℵ₀-bounded.     

Notes on combinatorial set theory

We shall prove some unconnected theorems: (1) (G.C.H.) \omega _{\alpha + 1} \to \left( {\omega _\alpha + \xi } \right)_2^2 when ℵ_α is regular, │ξ│⁺<ωα. (2) There is a Jonsson algebra in ℵ_α+n, and \aleph _{a + n} \not \to \left[ {\aleph _{a + n} } \right]_{\aleph _{a + n} }^{n + 1} if 2^{\aleph _{ - - } } = \aleph _{a + n} \cdot (3) If λ>ℵ₀ is a strong limit cardinal, then among the graphs with ≦λ vertices each of valence <λ there is a universal one. (4)(G.C.H.) If f is a set mapping on \omega _{a + 1} (ℵ_α regular) │f(x)∩f(y│<ℵ_α, then there is a free subset of order-type ζ for every ζ<ω_α+1.     

On normal precipitous ideals

An old question of T. Jech and K Prikry asks whether the existence of a precipitous ideal implies the existence of a normal precipitous one. The aim of the paper is to prove some results in the positive direction. In particular, it is shown that under some mild assumptions, the existence of a precipitous ideal over ℵ₁ implies the existence of a normal precipitous ideal over ℵ₁ once a Cohen subset is added to ℵ₂.     

A weak generalization of MA to higher cardinals

We generalized MA e.g., to ℵ₁-complete forcing, by strengthening the ℵ₂-C.C. condition which occurs in many proofs. We show some consequences of MA generalized, and show that we get a model of ZFC in which the modadic theory ofω ₂ is decidable. The author thanks the United States-israel Binational Foundation for partially supporting his research by Grant 1110.     

A weak version of ◊ which follows from 2ℵ 0<2ℵ 1

We prove that if CH holds (or even if 2^ℵ ₀ < 2^ℵ ₁), then a weak version of ◊ holds. This weak version of ◊ is a ◊-like principle, and is strong enough to yield some of the known consequences of ◊. The second author wishes to thank the United States-Israel Binational Foundation for partially supporting his research by Grant 1110.     

Chang’s conjecture for ℵω

We establish, starting from some assumptions of the order of magnitude of a huge cardinal, the consistency of (ℵ_ω+1,ℵ_ω)↠(ω₁,ω₀), as well as of some other transfer properties of the type (κ⁺,κ)↠(α⁺,α), where κ is singular.     

On a superatomic Boolean algebra which is not generated by a well-founded sublattice

Let b denote the unboundedness number of ω^ω. That is, b is the smallest cardinality of a subset such that for everyg∈ω^ω there isf ∈ F such that {n: g(n) ≤ f(n)}is infinite. A Boolean algebraB is wellgenerated, if it has a well-founded sublatticeL such thatL generatesB. We show that it is consistent with ZFC that , and there is a Boolean algebraB such thatB is not well-generated, andB is superatomic with cardinal sequence 〈ℵ₀, ℵ₁, ℵ₁, 1〉. This result is motivated by the fact that if the cardinal sequence of a Boolean algebraB is 〈ℵ₀, ℵ₀, λ, 1〉, andB is not well-generated, then λ≥b.     

Gently killing S-spaces

We produce a model of ZFC in which there are no locally compact first countable S-spaces, and in which 2^ℵ ₀<2^ℵ ₁. A consequence of this is that in this model there are no locally compact, separable, hereditarily normal spaces of size ℵ₁, answering a question of the second author [9]. The first author would like to thank The Hebrew University of Jerusalem for their support while the research in this paper was being carried out. The research of the second author was partially supported by NSF Grant DMS-9322613. The research of the third author was partially supported by NSF grant DMS-9704477 and the Israel Science Foundation founded by the Israel Academy of Sciences and Humanities. This is publication number 690 in the list of the third author.