{"title":"On classification of continuous first order theories","authors":"Karim Khanaki","doi":"10.1016/j.apal.2026.103729","DOIUrl":"10.1016/j.apal.2026.103729","url":null,"abstract":"<div><div>We present several new characterizations of <em>IP</em> (the independence property) and <em>SOP</em> (the strict order property) for continuous first-order logic and explore their connections to functional analysis and Banach space theory. Furthermore, we propose new dividing lines for unstable theories by examining subclasses of Baire-1 functions. We also explain why one should not expect a perfect analogue of Shelah's theorem—namely, that a theory is unstable if and only if it has <em>IP</em> or <em>SOP</em>—to hold for real-valued logics, particularly in the context of continuous logic.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 7","pages":"Article 103729"},"PeriodicalIF":0.6,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116732","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marcin Michalski, Robert Rałowski, Szymon Żeberski
{"title":"On algebraic sums, trees and ideals in the Cantor space","authors":"Marcin Michalski, Robert Rałowski, Szymon Żeberski","doi":"10.1016/j.apal.2026.103724","DOIUrl":"10.1016/j.apal.2026.103724","url":null,"abstract":"<div><div>We work in the Cantor space <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>ω</mi></mrow></msup></math></span>. The results of the paper adhere to the following pattern. Let <span><math><mi>I</mi><mo>∈</mo><mo>{</mo><mi>M</mi><mo>,</mo><mi>N</mi><mo>,</mo><mi>M</mi><mo>∩</mo><mi>N</mi><mo>,</mo><mi>E</mi><mo>}</mo></math></span> and <em>T</em> be a perfect, uniformly perfect or Silver tree. Then for every <span><math><mi>A</mi><mo>∈</mo><mi>I</mi></math></span> there exists <span><math><msup><mrow><mi>T</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>⊆</mo><mi>T</mi></math></span> of the same kind as <em>T</em> such that <span><math><mi>A</mi><mo>+</mo><munder><munder><mrow><mo>[</mo><msup><mrow><mi>T</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>]</mo><mo>+</mo><mo>[</mo><msup><mrow><mi>T</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>]</mo><mo>+</mo><mo>…</mo><mo>+</mo><mo>[</mo><msup><mrow><mi>T</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>]</mo></mrow><mo>︸</mo></munder><mrow><mi>n</mi><mtext>–times</mtext></mrow></munder><mo>∈</mo><mi>I</mi></math></span> for each <span><math><mi>n</mi><mo>∈</mo><mi>ω</mi></math></span>. We also prove weaker statements for splitting trees. For the case <span><math><mi>E</mi></math></span> we also provide a simple characterization of a basis of <span><math><mi>E</mi></math></span>. We use these results to prove that the algebraic sum of a generalized Luzin set and a generalized Sierpiński set belongs to <span><math><msub><mrow><mi>u</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>v</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>, provided that <span><math><mi>c</mi></math></span> is a regular cardinal.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 6","pages":"Article 103724"},"PeriodicalIF":0.6,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146024445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Positively closed Sh(B)-valued models","authors":"Kristóf Kanalas","doi":"10.1016/j.apal.2026.103726","DOIUrl":"10.1016/j.apal.2026.103726","url":null,"abstract":"<div><div>We study positively closed and strongly positively closed topos-valued models of coherent theories. Positively closed is a global notion (it is defined in terms of all possible outgoing homomorphisms), while strongly positively closed is a local notion (it only concerns the definable sets inside the model). For <strong>Set</strong>-valued models of coherent theories they coincide.</div><div>We prove that if <span><math><mi>E</mi><mo>=</mo><mi>S</mi><mi>h</mi><mo>(</mo><mi>B</mi><mo>,</mo><msub><mrow><mi>τ</mi></mrow><mrow><mi>c</mi><mi>o</mi><mi>h</mi></mrow></msub><mo>)</mo></math></span> for a complete Boolean algebra, then positively closed but not strongly positively closed <span><math><mi>E</mi></math></span>-valued models of coherent theories exist, yet, there is an alternative local property which characterizes positively closed <span><math><mi>E</mi></math></span>-valued models.</div><div>A large part of our discussion is given in the context of infinite quantifier geometric logic, dealing with the fragment <span><math><msubsup><mrow><mi>L</mi></mrow><mrow><mi>κ</mi><mi>κ</mi></mrow><mrow><mi>g</mi></mrow></msubsup></math></span> where <em>κ</em> is weakly compact.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 6","pages":"Article 103726"},"PeriodicalIF":0.6,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146079688","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Amorphous sets and dual Dedekind finiteness","authors":"Yifan Hu , Ruihuan Mao , Guozhen Shen","doi":"10.1016/j.apal.2026.103723","DOIUrl":"10.1016/j.apal.2026.103723","url":null,"abstract":"<div><div>A set <em>A</em> is dually Dedekind finite if every surjection from <em>A</em> onto <em>A</em> is injective; otherwise, <em>A</em> is dually Dedekind infinite. An amorphous set is an infinite set that cannot be partitioned into two infinite subsets. A strictly amorphous set is an amorphous set in which every partition has only finitely many non-singleton blocks. It is proved consistent with <span><math><mi>ZF</mi></math></span> (i.e., Zermelo–Fraenkel set theory without the axiom of choice) that there exists an amorphous set <em>A</em> whose power set <span><math><mi>P</mi><mo>(</mo><mi>A</mi><mo>)</mo></math></span> is dually Dedekind infinite, which gives a negative solution to a question proposed by Truss (1974) <span><span>[13]</span></span>. Nevertheless, we prove in <span><math><mi>ZF</mi></math></span> that, for all strictly amorphous sets <em>A</em> and all natural numbers <em>n</em>, <span><math><mi>P</mi><msup><mrow><mo>(</mo><mi>A</mi><mo>)</mo></mrow><mrow><mi>n</mi></mrow></msup></math></span> is dually Dedekind finite, which generalizes a result of Goldstern.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 6","pages":"Article 103723"},"PeriodicalIF":0.6,"publicationDate":"2026-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145950127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The computational content of multidimensional discontinuity","authors":"Rupert Hölzl , Keng Meng Ng","doi":"10.1016/j.apal.2026.103720","DOIUrl":"10.1016/j.apal.2026.103720","url":null,"abstract":"<div><div>The Weihrauch degrees are a tool to gauge the computational difficulty of mathematical problems. Often, what makes these problems hard is their discontinuity. We look at discontinuity in its purest form, that is, at otherwise constant functions that make a single discontinuous step along each dimension of their underlying space. This is an extension of previous work of Kihara, Pauly, Westrick from a single dimension to multiple dimensions. Among other results, we obtain strict hierarchies in the Weihrauch degrees, one of which orders mathematical problems by the richness of the truth-tables determining how discontinuous steps influence the output.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 5","pages":"Article 103720"},"PeriodicalIF":0.6,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146188106","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Generic torsion-free groups and Rubin actions","authors":"Thomas Koberda, Yash Lodha","doi":"10.1016/j.apal.2025.103704","DOIUrl":"10.1016/j.apal.2025.103704","url":null,"abstract":"<div><div>We use model theoretic forcing to prove that a generic countable torsion-free group does not admit any non-trivial locally moving action on a Hausdorff topological space, and yet admits a rich Rubin poset.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 5","pages":"Article 103704"},"PeriodicalIF":0.6,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145738714","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Groups elementarily equivalent to metabelian Baumslag – Solitar groups and regular bi-interpretability","authors":"Evelina Daniyarova , Alexei Myasnikov","doi":"10.1016/j.apal.2025.103695","DOIUrl":"10.1016/j.apal.2025.103695","url":null,"abstract":"<div><div>We prove that metabelian Baumslag<!--> <!-->–<!--> <!-->Solitar group <span><math><mrow><mi>BS</mi></mrow><mo>(</mo><mn>1</mn><mo>,</mo><mi>k</mi><mo>)</mo></math></span>, <span><math><mi>k</mi><mo>></mo><mn>1</mn></math></span>, is (strongly) regularly bi-interpretable with the ring of integers <span><math><mi>Z</mi></math></span>, and describe in algebraic terms all groups that are elementarily equivalent to <span><math><mrow><mi>BS</mi></mrow><mo>(</mo><mn>1</mn><mo>,</mo><mi>k</mi><mo>)</mo></math></span>.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 5","pages":"Article 103695"},"PeriodicalIF":0.6,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145658449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Constructive quantifier elimination with a focus on matrix rings","authors":"Max Illmer, Tim Netzer","doi":"10.1016/j.apal.2025.103706","DOIUrl":"10.1016/j.apal.2025.103706","url":null,"abstract":"<div><div>We give a sufficient condition for a model theoretic structure <em>B</em> to ‘inherit’ quantifier elimination from another structure <em>A</em>. This yields an alternative proof of one of the main results from <span><span>[8]</span></span>, namely quantifier elimination for certain matrix rings. The original proof uses model theory, and while it is very elegant and insightful, the proof we propose is much shorter and provides a constructive algorithm.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 5","pages":"Article 103706"},"PeriodicalIF":0.6,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145884440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Algebraic independence of the solutions of the classical Lotka-Volterra system","authors":"Yutong Duan, Joel Nagloo","doi":"10.1016/j.apal.2025.103707","DOIUrl":"10.1016/j.apal.2025.103707","url":null,"abstract":"<div><div>Let <span><math><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><msub><mrow><mi>y</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>)</mo><mo>,</mo><mo>…</mo><mo>,</mo><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>,</mo><msub><mrow><mi>y</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>)</mo></math></span> be distinct non-constant and non-degenerate solutions of the classical Lotka-Volterra system<span><span><span><math><msup><mrow><mi>x</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>=</mo><mi>a</mi><mi>x</mi><mi>y</mi><mo>+</mo><mi>b</mi><mi>x</mi><mspace></mspace><msup><mrow><mi>y</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>=</mo><mi>c</mi><mi>x</mi><mi>y</mi><mo>+</mo><mi>d</mi><mi>y</mi></math></span></span></span> where <span><math><mi>a</mi><mo>,</mo><mi>b</mi><mo>,</mo><mi>c</mi><mo>,</mo><mi>d</mi><mo>∈</mo><mi>C</mi><mo>∖</mo><mo>{</mo><mn>0</mn><mo>}</mo></math></span>. We show that if <em>d</em> and <em>b</em> are linearly independent over <span><math><mi>Q</mi></math></span>, then the solutions are algebraically independent over <span><math><mi>C</mi></math></span>, that is <span><math><mi>t</mi><mi>r</mi><mo>.</mo><mi>d</mi><mi>e</mi><msub><mrow><mi>g</mi></mrow><mrow><mi>C</mi></mrow></msub><mi>C</mi><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><msub><mrow><mi>y</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>x</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>,</mo><msub><mrow><mi>y</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>)</mo><mo>=</mo><mn>2</mn><mi>n</mi></math></span>. As a main part of the proof, we show that the set defined by the system in universal differential fields, with <em>d</em> and <em>b</em> linearly independent over <span><math><mi>Q</mi></math></span>, is strongly minimal and geometrically trivial. Our techniques also allows us to obtain partial results for some of the more general 2<em>d</em>-Lotka-Volterra system.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 5","pages":"Article 103707"},"PeriodicalIF":0.6,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145926009","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alan Dow , Raúl Figueroa-Sierra , Osvaldo Guzmán , Michael Hrušák
{"title":"The category dichotomy for ideals","authors":"Alan Dow , Raúl Figueroa-Sierra , Osvaldo Guzmán , Michael Hrušák","doi":"10.1016/j.apal.2025.103717","DOIUrl":"10.1016/j.apal.2025.103717","url":null,"abstract":"<div><div>We prove that there is an ideal on <em>ω</em> that is not Katětov below <span>nwd</span> and does not have restrictions above <span><math><mi>ED</mi></math></span>. We also prove that in the Laver model every tall <span>P</span>-ideal is Katětov-Blass above <span><math><msub><mrow><mi>ED</mi></mrow><mrow><mtext>fin</mtext></mrow></msub></math></span> and that it is consistent that every <span>Q</span><sup>+</sup> ideal is meager.</div></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"177 5","pages":"Article 103717"},"PeriodicalIF":0.6,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145976652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}