{"title":"Mutual algebraicity and cellularity","authors":"Samuel Braunfeld, Michael C. Laskowski","doi":"10.1007/s00153-021-00804-4","DOIUrl":"10.1007/s00153-021-00804-4","url":null,"abstract":"<div><p>We prove two results intended to streamline proofs about cellularity that pass through mutual algebraicity. First, we show that a countable structure <i>M</i> is cellular if and only if <i>M</i> is <span>(omega )</span>-categorical and mutually algebraic. Second, if a countable structure <i>M</i> in a finite relational language is mutually algebraic non-cellular, we show it admits an elementary extension adding infinitely many infinite MA-connected components. Towards these results, we introduce MA-presentations of a mutually algebraic structure, in which every atomic formula is mutually algebraic. This allows for an improved quantifier elimination and a decomposition of the structure into independent pieces. We also show this decomposition is largely independent of the MA-presentation chosen.</p></div>","PeriodicalId":48853,"journal":{"name":"Archive for Mathematical Logic","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2022-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50035655","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Equivalence of generics","authors":"Iian B. Smythe","doi":"10.1007/s00153-021-00813-3","DOIUrl":"10.1007/s00153-021-00813-3","url":null,"abstract":"<div><p>Given a countable transitive model of set theory and a partial order contained in it, there is a natural countable Borel equivalence relation on generic filters over the model; two are equivalent if they yield the same generic extension. We examine the complexity of this equivalence relation for various partial orders, focusing on Cohen and random forcing. We prove, among other results, that the former is an increasing union of countably many hyperfinite Borel equivalence relations, and hence is amenable, while the latter is neither amenable nor treeable.</p></div>","PeriodicalId":48853,"journal":{"name":"Archive for Mathematical Logic","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2022-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45280963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Hindman’s theorem for sums along the full binary tree, (Sigma ^0_2)-induction and the Pigeonhole principle for trees","authors":"Lorenzo Carlucci, Daniele Tavernelli","doi":"10.1007/s00153-021-00814-2","DOIUrl":"10.1007/s00153-021-00814-2","url":null,"abstract":"<div><p>We formulate a restriction of Hindman’s Finite Sums Theorem in which monochromaticity is required only for sums corresponding to rooted finite paths in the full binary tree. We show that the resulting principle is equivalent to <span>(Sigma ^0_2)</span>-induction over <span>(mathsf {RCA}_0)</span>. The proof uses the equivalence of this Hindman-type theorem with the Pigeonhole Principle for trees <span>({mathsf {T},}{mathsf {T}}^1)</span> with an extra condition on the solution tree.</p></div>","PeriodicalId":48853,"journal":{"name":"Archive for Mathematical Logic","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2022-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00153-021-00814-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50040683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Hindman’s theorem for sums along the full binary tree, \u0000 \u0000 \u0000 \u0000 $$Sigma ^0_2$$\u0000 \u0000 \u0000 Σ\u0000 2\u0000 0\u0000 \u0000 \u0000 -induction and the Pigeonhole principle for trees","authors":"L. Carlucci, Daniele Tavernelli","doi":"10.1007/s00153-021-00814-2","DOIUrl":"https://doi.org/10.1007/s00153-021-00814-2","url":null,"abstract":"","PeriodicalId":48853,"journal":{"name":"Archive for Mathematical Logic","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2022-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42724081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}