Scientific and pedagogical staff

Hefter Serhii Leonidovych

Candidate of Physical and Mathematical Sciences, Associate Professor, Associate Professor (part-time) of the Department of Fundamental Mathematics. Main place of work: B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, Senior Researcher of the Department of Function Theory

  • algebraic and arithmetic questions of the theory of differential and difference equations

Посилання на сторінки в наукових мережах:

  • Математичний аналіз
  • Functional Analysis
  • Banach algebras and spectral theory
  • Узагальнені функції
  • Вступ до теорії кілець
  • Analytic Number Theory
  1. R. Skurikhin, S. Gefter, E. Karolinsky, Closed equivalence relations on compact spaces and pairs of commutative 𝐶*-algebras: a categorical approach, Visnyk of V. N. Karazin Kharkiv National University. Ser. Mathematics, Applied Mathematics and Mechanics, Vol. 102, 2025, p. 57–67. DOI: https://doi.org/10.26565/2221-5646-2025-102-04
  2. Sergiy L. Gefter and Aleksey L. Piven’, Nonlinear Partial Differential Equations in Module of Copolynomials over a Commutative Ring, Journal of Mathematical Physics, Analysis, Geometry. (2025), vol. 21, Issue 3, р. 319-345.     https://doi.org/10.15407/mag21.03.05
  3. Sergiy L. Gefter and Aleksey L. Piven’, Partial Differential Equations in Module of Copolynomials over a Commutative Ring, Journal of Mathematical Physics, Analysis, Geometry. (2025), vol. 21, Issue 1, p. 56–83. https://doi.org/10.15407/mag21.01.03
  4. Sergiy L. Gefter and Aleksey L. Piven’, Formal functional calculus for copolynomials over a commutative ring,  Algebra and Discrete Mathematics, vol. 39, Issue 2, p. 207–224. (2025)  http://dx.doi.org/10.12958/adm2352
  5. Sergiy L. Gefter and Aleksey L. Piven’, Some class of nonlinear partial differential equations in the ring of copolynomials over a commutative ring, Front. Appl. Math. Stat. 10:1466569 (2024) https://doi.org/10.3389/fams.2024.1466569
  6. Hefter, S.L., Goncharuk, A.B. Linear Differential Equation with Inhomogeneity in the Form of a Formal Power Series Over a Ring with Non-Archimedean Valuation. Ukr Math J 74, 1668–1685 (2023). https://doi.org/10.1007/s11253-023-02163-0
  7. Gefter, S., Goncharuk, A., Piven’, A., Implicit Linear First Order Difference Equations Over Commutative Rings, Springer Proceedings in Mathematics & Statistics, vol. 416. Springer, Cham, (2023), P. 199-216. https://link.springer.com/chapter/10.1007/978-3-031-25225-9_10
  8. Gefter, S. L., and O. L. Piven, Differential operators of infinite order in the module of formal generalized functions and in the ring of formal power series, Ukrainian Mathematical Journal, vol. 74, no. 6, July 2022, p. 784 -799. https://link.springer.com/article/10.1007/s11253-022-02116-z
  9. S.L. Gefter, A.L. Piven’, Implicit Linear Nonhomogeneous Difference Equation over ℤ with a Random Right-Hand Side, Journal of Mathematical Physics, Analysis, Geometry, (2022), vol. 18, Issue1, 105–117.https://jmag.ilt.kharkov.ua/jmag/pdf/18/jm18-0105e.pdf
  10. S.L. Gefter, A.L. Piven’, Linear Partial Differential Equations in Module of Formal Generalized Functions over Commutative Ring, Journal of Mathematical Sciences (United States), (2021), vol. 257, 579–596. 
     https://link.springer.com/article/10.1007/s10958-021-05505-0
  11. Gefter, S.L., Piven’, A.L. Implicit Linear Differential-Difference Equations in the Module of Formal Generalized Functions over a Commutative Ring. J. Math. Sci. 255, 409–422 (2021). https://link.springer.com/article/10.1007/s10958-021-05381-8
  1. Sergiy Gefter and Mariia Stas, A GEOMETRIC APPROACH TO THE MOIVRE-STIRLING FORMULA, XVIII International Scientific and Practical Conference «Academic and University Science: Results and Prospects», National University «Yurii Kondratyuk Poltava Polytechnic», 2025-12-09 – 2025-12-12 https://nupp.edu.ua/uploads/files/0/events/conf/2025/xviii-aunrp/prog.pdf
  2. Gefter S., Karolinsky E., Skurihin R., Categorical Version of Shilov’s Theorem on Closed Equivalence Relations, “Algebraic and geometric methods of analysis”, May 26-29, 2025, Odesa, Ukraine, p. 103. https://www.imath.kiev.ua/~topology/conf/agma2025/agma2025-theses.pdf
  3. Gefter S., Piven’ O., Nonlinear partial differential equations in module of copolynomials over a commutative ring, International Conference dedicated to the 145th anniversary of Hans Hahn's birth, September 23-27, 2024, Chernivtsi National University named after Yuriy Fedkovych. – Chernivtsi: 2024, P. 130–131. https://hahn.chnu.edu.ua/media/ntbkpax0/book-of-abstracts.pdf
  4. Sergiy Gefter and Aleksey Piven’, Representations of solutions of some nonlinear PDEs in the form of series in powers of the -function, Bogolyubov Kyiv Conference “Problems of Theoretical and Mathematical Physics”, Kyiv, Ukraine, September 24-26, 2024 Book of abstracts.–P.110 https://indico.bitp.kiev.ua/event/13/book-of-abstracts.pdf
  5. Gefter, S., Piven’A., Linear differential operators of infinite order in the module of copolynomials, Proceedings of the international scientific conference “Mathematics and Information Technologies», dedicated to the 55th anniversary of the Faculty of Mathematics and Informatics, Chernivtsi, Ukraine, September 28–30, 2023, Chernivtsi National University.–Chernivtsi: 2023.– P. 52–55. https://fmi.chnu.edu.ua/media/qhufs0d5/materialy-mizhnorodnoi-naukovoi-konferentsii-fmi55.pdf
  6. Sergey Gefter, Aleksey Piven’, Partial differential equations in the module of copolynomials in several variables over a commutative ring// 6-th International Conference “Differential Equations and Control Theory’’ DECT-2023:Book of abstracts. Kharkiv: V.N. Karazin Kharkiv University, 2023.– P.15–16. https://appmath.univer.kharkov.ua/pdf/DECT2023/DECT2023_Book.pdf
  7. Anna Goncharuk, Sergey Gefter, Aleksey Piven’, Periodic and quasi-polynomial solutions of implicit linear difference equations over commutative rings, ICDEA 2022, 27th International Conference on Difference Equations and Applications,18-22 July 2022, Paris-Saclay, France, P. 137.  https://icdea2022.sciencesconf.org/data/pages/icdea2022_leaflet_v5_1_.pdf
  8. A.B. Goncharuk; S.L. Gefter; O.L. Piven’, Quasi-polynomial solutions of implicit linear difference equations over a local commutative ring, THE INTERNATIONAL ONLINE CONFERENCE “CURRENT TRENDS IN ABSTRACT AND APPLIED ANALYSIS”, Book of Abstracts, Ivano-Frankivsk, 2022 , P.32  https://conference.pu.if.ua/cta/BookOfAbstracts.pdf
  9. S. Gefter, A. Piven’, Linear differential equations in the module of copolynomials, Vth International conference “Differential equations and control theory”, Book of abstracts, 2021, P. 18 .  https://appmath.univer.kharkov.ua/pdf/DECT2021/DECT2021_Book.pdf