Annals of Pure and Applied Logic ( IF 0.6 ) Pub Date : 2020-02-19 , DOI: 10.1016/j.apal.2020.102791 Brent Cody
Hellsten [15] gave a characterization of -indescribable subsets of a -indescribable cardinal in terms of a natural filter base: when κ is a -indescribable cardinal, a set is -indescribable if and only if for every n-club . We generalize Hellsten's characterization to -indescribable subsets of , which were first defined by Baumgartner. First we show that under reasonable assumptions the -indescribability ideal on equals the minimal strongly normal ideal on , which is different from . We then formulate a notion of n-club subset of and prove that a set is -indescribable if and only if for every n-club . We also prove that elementary embeddings considered by Schanker [26] witnessing near supercompactness lead to the definition of a normal ideal on , and indeed, this ideal is equal to Baumgartner's ideal of non–-indescribable subsets of . Additionally, as applications of these results we answer a question of Cox-Lücke [10] about -layered posets, provide a characterization of -indescribable subsets of in terms of generic elementary embeddings and prove several results involving a two-cardinal weakly compact diamond principle.
中文翻译:
弱紧凑理想的上刻划P κ λ
Hellsten [15]给出了 -a的不可描述子集 -根据自然过滤器基数可描述的基数:当κ为-难以描述的主教,一套 是 -仅当且仅当- 每个n俱乐部。我们将Hellsten的特征概括为的-无法描述的子集 ,最初由包姆加特纳(Baumgartner)定义。首先,我们证明在合理的假设下-难以刻画的理想 等于最小强法线理想 上 ,这与 。然后,我们提出n -club子集的概念 并证明一套 是 -仅当且仅当- 每个n俱乐部。我们还证明,由Schanker [26]考虑的基本嵌入见证了近超紧致性,从而导致了对标准理想的定义。,实际上,这个理想等于鲍姆加特纳(Baumgartner)的非理想的-无法描述的子集 。另外,作为这些结果的应用,我们回答了Cox-Lücke[10]关于层状的姿势,可以表征 的-无法描述的子集 在通用基本嵌入方面,并证明了涉及两个基本弱密实钻石原理的几个结果。