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Istvan Németi [33]I. Németi [23]
  1. Christian Wüthrich, Hajnal Andréka & István Németi, A Twist in the Geometry of Rotating Black Holes: Seeking the Cause of Acausality.
    We investigate Kerr–Newman black holes in which a rotating charged ring-shaped singularity induces a region which contains closed timelike curves (CTCs). Contrary to popular belief, it turns out that the time orientation of the CTC is oppo- site to the direction in which the singularity or the ergosphere rotates. In this sense, CTCs “counter-rotate” against the rotating black hole. We have similar results for all spacetimes sufficiently familiar to us in which rotation induces CTCs. This motivates our conjecture that perhaps (...)
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  2. H. Andréka, J. van Benthem & I. Németi (forthcoming). Modal Logics and Bounded First-Order Fragments'. Journal of Philosophical Logic.
     
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  3. Hajnal Andréka, Judit X. Madarász, István Németi & Gergely Székely (2012). A Logic Road From Special Relativity to General Relativity. Synthese 186 (3):633 - 649.
    We present a streamlined axiom system of special relativity in first-order logic. From this axiom system we "derive" an axiom system of general relativity in two natural steps. We will also see how the axioms of special relativity transform into those of general relativity. This way we hope to make general relativity more accessible for the non-specialist.
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  4. Hajnal Andréka, Judit X. Madarász, István Németi & Gergely Székely, A Logic Road From Special to General Relativity.
    We present a streamlined axiom system of special relativity in firs-order logic. From this axiom system we ``derive'' an axiom system of general relativity in two natural steps. We will also see how the axioms of special relativity transform into those of general relativity. This way we hope to make general relativity more accessible for the non-specialist.
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  5. I. Németi & A. Simon (2009). Weakly Higher Order Cylindric Algebras and Finite Axiomatization of the Representables. Studia Logica 91 (1):53 - 62.
    We show that the variety of n -dimensional weakly higher order cylindric algebras, introduced in Németi [9], [8], is finitely axiomatizable when n > 2. Our result implies that in certain non-well-founded set theories the finitization problem of algebraic logic admits a positive solution; and it shows that this variety is a good candidate for being the cylindric algebra theoretic counterpart of Tarski’s quasi-projective relation algebras.
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  6. H. Andréka, J. X. Madarász, I. Németi & G. Székely (2008). Axiomatizing Relativistic Dynamics Without Conservation Postulates. Studia Logica 89 (2):163 - 186.
    A part of relativistic dynamics is axiomatized by simple and purely geometrical axioms formulated within first-order logic. A geometrical proof of the formula connecting relativistic and rest masses of bodies is presented, leading up to a geometric explanation of Einstein's famous E = mc² . The connection of our geometrical axioms and the usual axioms on the conservation of mass, momentum and four-momentum is also investigated.
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  7. Hajnal Andréka, Judit Madarász X., István Németi & Gergely Székely (2008). Axiomatizing Relativistic Dynamics Without Conservation Postulates. Studia Logica 89 (2):163 - 186.
    A part of relativistic dynamics is axiomatized by simple and purely geometrical axioms formulated within first-order logic. A geometrical proof of the formula connecting relativistic and rest masses of bodies is presented, leading up to a geometric explanation of Einstein’s famous E = mc 2. The connection of our geometrical axioms and the usual axioms on the conservation of mass, momentum and four-momentum is also investigated.
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  8. Hajnal Andréka, István Németi & Tarek Sayed Ahmed (2008). Omitting Types for Finite Variable Fragments and Complete Representations of Algebras. Journal of Symbolic Logic 73 (1):65-89.
    We give a novel application of algebraic logic to first order logic. A new, flexible construction is presented for representable but not completely representable atomic relation and cylindric algebras of dimension n (for finite n > 2) with the additional property that they are one-generated and the set of all n by n atomic matrices forms a cylindric basis. We use this construction to show that the classical Henkin-Orey omitting types theorem fails for the finite variable fragments of first order (...)
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  9. Judit X. Madarász, István Németi & Gergely Székely (2006). Twin Paradox and the Logical Foundation of Relativity Theory. Foundations of Physics 36 (5):681-714.
    We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization Specrel of special relativity from the literature. Specrel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove the usual relativistic properties of (...)
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  10. István Németi & Gyula Dávid (2006). Relativistic Computers and the Turing Barrier. Journal of Applied Mathematics and Computation 178:118--42.
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  11. Judit X. Madarasz, Istvan Nemeti & Gergely Szekely, First-Order Logic Foundation of Relativity Theories.
    Motivation and perspective for an exciting new research direction interconnecting logic, spacetime theory, relativity--including such revolutionary areas as black hole physics, relativistic computers, new cosmology--are presented in this paper. We would like to invite the logician reader to take part in this grand enterprise of the new century. Besides general perspective and motivation, we present initial results in this direction.
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  12. Hajnal Andréka, Judit X. Madarász & István Németi (2005). Mutual Definability Does Not Imply Definitional Equivalence, a Simple Example. Mathematical Logic Quarterly 51 (6):591-597.
    We give two theories, Th1 and Th2, which are explicitly definable over each other , but are not definitionally equivalent. The languages of the two theories are disjoint.
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  13. Judit X. Madarász, István Németi & Csaba Toke (2004). On Generalizing the Logic-Approach to Space-Time Towards General Relativity: First Steps. In Vincent F. Hendricks (ed.), First-Order Logic Revisited. Logos 225--268.
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  14. H. Andreka, S. Givant, I. Nemeti & Roger D. Maddux (2003). REVIEWS-Decision Problems for Equational Theories of Relation Algebras. Bulletin of Symbolic Logic 9 (1):37-38.
  15. Gábor Etesi & István Németi (2002). Non-Turing Computations Via Malament-Hogarth Space-Times. International Journal of Theoretical Physics 41:341--70.
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  16. Tarek Sayed Ahmed & Istvan Németi (2001). On Neat Reducts of Algebras of Logic. Studia Logica 68 (2):229-262.
    SC , CA , QA and QEA stand for the classes of Pinter's substitution algebras, Tarski's cylindric algebras, Halmos' quasipolyadic algebras, and quasipolyadic equality algebras of dimension , respectively. Generalizing a result of Németi on cylindric algebras, we show that for K {SC, CA, QA, QEA} and ordinals , the class Nr K of -dimensional neat reducts of -dimensional K algebras, though closed under taking homomorphic images and products, is not closed under forming subalgebras (i.e. is not a variety) if (...)
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  17. I. Németi & I. Sain (2000). Editorial. Logic Journal of the Igpl 8 (4):379-381.
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  18. István Németi & Gábor Sági (2000). On the Equational Theory of Representable Polyadic Equality Algebras. Journal of Symbolic Logic 65 (3):1143-1167.
    Among others we will prove that the equational theory of ω dimensional representable polyadic equality algebras (RPEA ω 's) is not schema axiomatizable. This result is in interesting contrast with the Daigneault-Monk representation theorem, which states that the class of representable polyadic algebras is finite schema-axiomatizable (and hence the equational theory of this class is finite schema-axiomatizable, as well). We will also show that the complexity of the equational theory of RPEA ω is also extremely high in the recursion theoretic (...)
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  19. H. Andréka, I. Hodkinson & I. Németi (1999). Finite Algebras of Relations Are Representable on Finite Sets. Journal of Symbolic Logic 64 (1):243-267.
    Using a combinatorial theorem of Herwig on extending partial isomorphisms of relational structures, we give a simple proof that certain classes of algebras, including Crs, polyadic Crs, and WA, have the `finite base property' and have decidable universal theories, and that any finite algebra in each class is representable on a finite set.
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  20. Hajnal Andréka, Steven Givant, Szabolcs Mikulás, István Németi & András Simon (1998). Notions of Density That Imply Representability in Algebraic Logic. Annals of Pure and Applied Logic 91 (2-3):93-190.
    Henkin and Tarski proved that an atomic cylindric algebra in which every atom is a rectangle must be representable . This theorem and its analogues for quasi-polyadic algebras with and without equality are formulated in Henkin, Monk and Tarski [13]. We introduce a natural and more general notion of rectangular density that can be applied to arbitrary cylindric and quasi-polyadic algebras, not just atomic ones. We then show that every rectangularly dense cylindric algebra is representable, and we extend this result (...)
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  21. Hajnal Andréka, Robert Goldblatt & István Németi (1998). Relativised Quantification: Some Canonical Varieties of Sequence-Set Algebras. Journal of Symbolic Logic 63 (1):163-184.
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  22. Hajnal Andréka, István Németi & Johan van Benthem (1998). Modal Languages and Bounded Fragments of Predicate Logic. Journal of Philosophical Logic 27 (3):217 - 274.
  23. Hajnal Andréka, István Németi & Johan van Benthem (1998). Modal Languages and Bounded Fragments of Predicate Logic. Journal of Philosophical Logic 27 (3):217-274.
    What precisely are fragments of classical first-order logic showing “modal” behaviour? Perhaps the most influential answer is that of Gabbay 1981, which identifies them with so-called “finite-variable fragments”, using only some fixed finite number of variables (free or bound). This view-point has been endorsed by many authors (cf. van Benthem 1991). We will investigate these fragments, and find that, illuminating and interesting though they are, they lack the required nice behaviour in our sense. (Several new negative results support this claim.) (...)
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  24. H. Andréka, I. NÉmeti & T. Sayed Ahmed (1997). On Neat Reducts of Algebras of Logic', Presented in Logic Colloquium 1996, Abstract Appeared in The. Bulletin of Symbolic Logic 3 (2):249.
     
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  25. I. Nemeti (1997). Strong Representability of Fork Algebras, a Set Theoretic Foundation. Logic Journal of the Igpl 5 (1):3-23.
    This paper is about pairing relation algebras as well as fork algebras and related subjects. In the 1991-92 fork algebra papers it was conjectured that fork algebras admit a strong representation theorem . Then, this conjecture was disproved in the following sense: a strong representation theorem for all abstract fork algebras was proved to be impossible in most set theories including the usual one as well as most non-well-founded set theories. Here we show that the above quoted conjecture can still (...)
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  26. I. Nemeti & A. Simon (1997). Relation Algebras From Cylindric and Polyadic Algebras. Logic Journal of the Igpl 5 (4):575-588.
    This paper is a survey of recent results concerning connections between relation algebras , cylindric algebras and polyadic equality algebras . We describe exactly which subsets of the standard axioms for RA are needed for axiomatizing RA over the RA-reducts of CA3's, and we do the same for the class SA of semi-associative relation algebras. We also characterize the class of RA-reducts of PEA3's. We investigate the interconnections between the RA-axioms within CA3 in more detail, and show that only four (...)
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  27. Hajnal Andréka, Ivo Düntsch & István Németi (1995). Expressibility of Properties of Relations. Journal of Symbolic Logic 60 (3):970-991.
    We investigate in an algebraic setting the question of which logical languages can express the properties integral, permutational, and rigid for algebras of relations.
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  28. Hajnal Andréka, Steven Givant & István Németi (1995). Perfect Extensions and Derived Algebras. Journal of Symbolic Logic 60 (3):775-796.
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  29. Hajnal Andreka, Johan van Benthem & Istvan Nemeti (1995). Back and Forth Between Modal Logic and Classical Logic. Logic Journal of the Igpl 3 (5):685-720.
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  30. ágnes Kurucz, István Németi, Ildikó Sain & András Simon (1995). Decidable and Undecidable Logics with a Binary Modality. Journal of Logic, Language and Information 4 (3):191-206.
    We give an overview of decidability results for modal logics having a binary modality. We put an emphasis on the demonstration of proof-techniques, and hope that this will also help in finding the borderlines between decidable and undecidable fragments of usual first-order logic.
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  31. Maarten Marx, Szabolcs Mikul & István Németi (1995). Taming Logic. Journal of Logic, Language and Information 4 (3):207-226.
    In this paper, we introduce a general technology, calledtaming, for finding well-behaved versions of well-investigated logics. Further, we state completeness, decidability, definability and interpolation results for a multimodal logic, calledarrow logic, with additional operators such as thedifference operator, andgraded modalities. Finally, we give a completeness proof for a strong version of arrow logic.
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  32. I. Nemeti, I. Sain & A. Simon (1995). Undecidability of the Equational Theory of Some Classes of Residuated Boolean Algebras with Operators. Logic Journal of the Igpl 3 (1):93-105.
    We show the undecidability of the equational theories of some classes of BAOs with a non-associative, residuated binary extra-Boolean operator. These results solve problems in Jipsen [9], Pratt [21] and Roorda [22], [23]. This paper complements Andréka-Kurucz-Németi-Sain-Simon [3] where the emphasis is on BAOs with an associative binary operator.
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  33. H. Andréka, Á Kurucz & I. Németi (1994). Connections Between Axioms of Set Theory and Basic Theorems of Universal Algebra. Journal of Symbolic Logic 59 (3):912-923.
    One of the basic theorems in universal algebra is Birkhoff's variety theorem: the smallest equationally axiomatizable class containing a class K of algebras coincides with the class obtained by taking homomorphic images of subalgebras of direct products of elements of K. G. Gratzer asked whether the variety theorem is equivalent to the Axiom of Choice. In 1980, two of the present authors proved that Birkhoff's theorem can already be derived in ZF. Surprisingly, the Axiom of Foundation plays a crucial role (...)
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  34. Hajnal Andréka, Steven Givant & István Németi (1994). The Lattice of Varieties of Representable Relation Algebras. Journal of Symbolic Logic 59 (2):631-661.
    We shall show that certain natural and interesting intervals in the lattice of varieties of representable relation algebras embed the lattice of all subsets of the natural numbers, and therefore must have a very complicated lattice-theoretic structure.
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  35. Istvan Nemeti & Hajnal Andreka (1994). General Algebraic Logic: A Perspective on “What is Logic”. In Dov M. Gabbay (ed.), What is a Logical System? Oxford University Press
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  36. A. Kurucz, I. Nemeti, I. Sain & A. Simon (1993). Undecidable Varieties of Semilattice—Ordered Semigroups, of Boolean Algebras with Operators, and Logics Extending Lambek Calculus. Logic Journal of the Igpl 1 (1):91-98.
    We prove that the equational theory of a semigroups becomes undecidable if we add a semilattice structure with a ‘touch of symmetric difference’. As a corollary we obtain that the variety of all Boolean algebras with an associative binary operator has a ‘hereditarily’ undecidable equational theory. Our results have implications in logic, e.g. they imply undecidability of modal logics extending the Lambek Calculus and undecidability of Arrow Logics with an associative arrow modality.
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  37. H. Andréka, J. Donald Monk, I. Németi, Bolyai János Matematikai Társulat & Association of Symbolic Logic (1991). Algebraic Logic. Monograph Collection (Matt - Pseudo).
  38. I. Németi (1991). Shortened Version Appeared As. Studia Logica 50 (3-4):458-569.
     
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  39. István Németi (1991). Algebraization of Quantifier Logics, an Introductory Overview. Studia Logica 50 (3-4):485 - 569.
    This paper is an introduction: in particular, to algebras of relations of various ranks, and in general, to the part of algebraic logic algebraizing quantifier logics. The paper has a survey character, too. The most frequently used algebras like cylindric-, relation-, polyadic-, and quasi-polyadic algebras are carefully introduced and intuitively explained for the nonspecialist. Their variants, connections with logic, abstract model theory, and further algebraic logics are also reviewed. Efforts were made to make the review part relatively comprehensive. In some (...)
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  40. H. Andréka, I. Németi & R. J. Thompson (1990). Weak Cylindric Set Algebras and Weak Subdirect Indecomposability. Journal of Symbolic Logic 55 (2):577-588.
    In this note we prove that the abstract property "weakly subdirectly indecomposable" does not characterize the class IWs α of weak cylindric set algebras. However, we give another (similar) abstract property characterizing IWs α . The original property does characterize the directed unions of members of $\mathrm{IWs}_alpha \operatorname{iff} \alpha$ is countable. Free algebras will be shown to satisfy the original property.
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  41. Istvan Nemeti (1990). Review: Alfred Tarski, Steven Givant, A Formalization of Set Theory Without Variables. [REVIEW] Journal of Symbolic Logic 55 (1):350-352.
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  42. H. Andréka, M. Ferenczi, I. Németi & Gy Serény (1989). Algebraic Logic Conference. Journal of Symbolic Logic 54 (2):686.
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  43. H. Andréka, W. Craig & I. Németi (1988). A System of Logic for Partial Functions Under Existence-Dependent Kleene Equality. Journal of Symbolic Logic 53 (3):834-839.
  44. I. Németi (1987). On Varieties of Cylindric Algebras with Applications to Logic. Annals of Pure and Applied Logic 36 (3):235-277.
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  45. L. Henkin, J. D. Monk, A. Tarski, H. Andréka & I. Németi (1986). Cylindric Set Algebras. Studia Logica 45 (2):223-225.
     
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  46. H. Andréka & I. Németi (1985). On the Number of Generators of Cylindric Algebras. Journal of Symbolic Logic 50 (4):865-873.
  47. I. Németi (1985). Cylindric-Relativised Set Algebras Have Strong Amalgamation. Journal of Symbolic Logic 50 (3):689-700.
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  48. István Németi (1983). The Class of Neat-Reducts of Cylindric Algebras is Not a Variety but is Closed with Respect to ${\Rm HP}$. Notre Dame Journal of Formal Logic 24 (3):399-409.
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  49. Hien Huy Bui & István Németi (1981). Problems with the Category Theoretic Notions of Ultraproducts. Bulletin of the Section of Logic 10 (3):122-126.
    In this paper we try to initiate a search for an explicite and direct denition of ultraproducts in categories which would share some of the attractive properties of products, coproducts, limits, and related category theoretic notions. Consider products as a motivating example.
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  50. Hajnal Andreka, Peter Burmeister & Istvan Nemeti (1980). Quasi Equational Logic Of Partial Algebras. Bulletin of the Section of Logic 9 (4):193-197.
     
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