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<article article-type="research-article" dtd-version="1.3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:lang="ru"><front><journal-meta><journal-id journal-id-type="publisher-id">izvuzmath</journal-id><journal-title-group><journal-title xml:lang="ru">Известия высших учебных заведений. Математика</journal-title><trans-title-group xml:lang="en"><trans-title>Izvestiya Vysshikh Uchebnykh Zavedenii. Matematika</trans-title></trans-title-group></journal-title-group><issn pub-type="ppub">0021-3446</issn><issn pub-type="epub">2076-4626</issn><publisher><publisher-name>Казанский (Приволжский) федеральный университет</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.26907/0021-3446-2024-4-89-93</article-id><article-id custom-type="elpub" pub-id-type="custom">izvuzmath-70</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="ru"><subject>Статьи</subject></subj-group></article-categories><title-group><article-title>Неразрешимость одноместных PFP-операторов без вложения в теории одного следования</article-title><trans-title-group xml:lang="en"><trans-title>On undecidability of unary non-nested PFP-operators for one successor function theory</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Секорин</surname><given-names>В. С.</given-names></name><name name-style="western" xml:lang="en"><surname>Sekorin</surname><given-names>V. S.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Всеслав Станиславович Секоринул. Желябова, д. 33, г. Тверь, 170100</p></bio><bio xml:lang="en"><p>Vseslav Stanislavovich Sekorin33 Zhelyabova str., Tver, 170100</p></bio><email xlink:type="simple">vssekorin@gmail.com</email><xref ref-type="aff" rid="aff-1"/></contrib></contrib-group><aff-alternatives id="aff-1"><aff xml:lang="ru"><institution>Тверской государственный университет</institution><country>Россия</country></aff><aff xml:lang="en"><institution>Tver State University</institution><country>Russian Federation</country></aff></aff-alternatives><pub-date pub-type="collection"><year>2024</year></pub-date><pub-date pub-type="epub"><day>24</day><month>04</month><year>2024</year></pub-date><volume>0</volume><issue>4</issue><fpage>89</fpage><lpage>93</lpage><permissions><copyright-statement>Copyright &amp;#x00A9; Секорин В.С., 2024</copyright-statement><copyright-year>2024</copyright-year><copyright-holder xml:lang="ru">Секорин В.С.</copyright-holder><copyright-holder xml:lang="en">Sekorin V.S.</copyright-holder><license xml:lang="ru" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>Данная работа распространяется под лицензией Creative Commons Attribution 4.0.</license-p></license><license xml:lang="en" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>This work is licensed under a Creative Commons Attribution 4.0 License.</license-p></license></permissions><self-uri xlink:href="https://izvuzmath.elpub.ru/jour/article/view/70">https://izvuzmath.elpub.ru/jour/article/view/70</self-uri><abstract><p>В данной работе мы исследуем разрешимость расширений логики первого порядка. Например, в работах А. С. Золотова показано, что логика с унарным оператором транзитивного замыкания для теории следования является разрешимой. Мы показываем, что в аналогичной ситуации логика с унарным оператором частичной неподвижной точки разрешимой не является. Для этого мы сводим проблему остановки счетчиковой машины к проблеме истинности формулы. При этом используется только один оператор частичной неподвижной точки, он является унарным, невложенным и применяется к универсальной или экзистенциальной формуле.</p></abstract><trans-abstract xml:lang="en"><p>We investigate the decidability of first-order logic extensions. For example, it is established in A. S. Zolotov’s works that a logic with a unary transitive closure operator for the one successor theory is decidable. We show that in a similar case, a logic with a unary partial fixed point operator is undecidable. For this purpose, we reduce the halting problem for the counter machine to the problem of truth of the underlying formula. This reduction uses only one unary non-nested partial fixed operator that is applied to a universal or existential formula.</p></trans-abstract><kwd-group xml:lang="ru"><kwd>логика первого порядка</kwd><kwd>частичная фиксированная точка</kwd><kwd>неразрешимость</kwd></kwd-group><kwd-group xml:lang="en"><kwd>first-order logic</kwd><kwd>partial fixed point</kwd><kwd>undecidability</kwd></kwd-group></article-meta></front><back><ref-list><title>References</title><ref id="cit1"><label>1</label><citation-alternatives><mixed-citation xml:lang="ru">Aho A., Ulman J.D. Universality of data retrieval languages, Proceedings of the 6th ACM SIGACT-SIGPLAN Symposium on Principles of Programming Languages POPL ’79, 110–119 (1979).</mixed-citation><mixed-citation xml:lang="en">Aho A., Ulman J.D. 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