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Profile: Jouko Väänänen (University of Helsinki, University of Amsterdam)
  1. Daisuke Ikegami & Jouko Väänänen (2015). Boolean-Valued Second-Order Logic. Notre Dame Journal of Formal Logic 56 (1):167-190.
    In so-called full second-order logic, the second-order variables range over all subsets and relations of the domain in question. In so-called Henkin second-order logic, every model is endowed with a set of subsets and relations which will serve as the range of the second-order variables. In our Boolean-valued second-order logic, the second-order variables range over all Boolean-valued subsets and relations on the domain. We show that under large cardinal assumptions Boolean-valued second-order logic is more robust than full second-order logic. Its (...)
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  2. Juliette Kennedy & Jouko Väänänen (2015). Aesthetics and the Dream of Objectivity: Notes From Set Theory. Inquiry 58 (1):83-98.
    In this paper, we consider various ways in which aesthetic value bears on, if not serves as evidence for, the truth of independent statements in set theory.... the aesthetic issue, which in practice will also for me be the decisive factor—John von Neumann, letter to Carnap, 1931For me, it is the aesthetics which may very well be the final arbiter—P. J. Cohen, 2002.
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  3. Jouko Väänänen (2015). Categoricity and Consistency in Second-Order Logic. Inquiry 58 (1):20-27.
    We analyse the concept of a second-order characterisable structure and divide this concept into two parts—consistency and categoricity—with different strength and nature. We argue that categorical characterisation of mathematical structures in second-order logic is meaningful and possible without assuming that the semantics of second-order logic is defined in set theory. This extends also to the so-called Henkin structures.
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  4. Jouko Väänänen (2015). Pursuing Logic Without Borders. In Andrés Villaveces, Roman Kossak, Juha Kontinen & Åsa Hirvonen (eds.), Logic Without Borders: Essays on Set Theory, Model Theory, Philosophical Logic and Philosophy of Mathematics. De Gruyter. 403-416.
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  5. Jouko Väänänen & Lauri Hella (2015). The Size of a Formula as a Measure of Complexity. [REVIEW] In Andrés Villaveces, Roman Kossak, Juha Kontinen & Åsa Hirvonen (eds.), Logic Without Borders: Essays on Set Theory, Model Theory, Philosophical Logic and Philosophy of Mathematics. De Gruyter. 193-214.
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  6. Jouko Väänänen & Tong Wang (2015). Internal Categoricity in Arithmetic and Set Theory. Notre Dame Journal of Formal Logic 56 (1):121-134.
    We show that the categoricity of second-order Peano axioms can be proved from the comprehension axioms. We also show that the categoricity of second-order Zermelo–Fraenkel axioms, given the order type of the ordinals, can be proved from the comprehension axioms. Thus these well-known categoricity results do not need the so-called “full” second-order logic, the Henkin second-order logic is enough. We also address the question of “consistency” of these axiom systems in the second-order sense, that is, the question of existence of (...)
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  7. Erich Grädel & Jouko Väänänen (2013). Dependence and Independence. Studia Logica 101 (2):399-410.
    We introduce an atomic formula ${\vec{y} \bot_{\vec{x}}\vec{z}}$ intuitively saying that the variables ${\vec{y}}$ are independent from the variables ${\vec{z}}$ if the variables ${\vec{x}}$ are kept constant. We contrast this with dependence logic ${\mathcal{D}}$ based on the atomic formula = ${(\vec{x}, \vec{y})}$ , actually equivalent to ${\vec{y} \bot_{\vec{x}}\vec{y}}$ , saying that the variables ${\vec{y}}$ are totally determined by the variables ${\vec{x}}$ . We show that ${\vec{y} \bot_{\vec{x}}\vec{z}}$ gives rise to a natural logic capable of formalizing basic intuitions about independence and dependence. (...)
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  8. Juha Kontinen & Jouko Väänänen (2013). Axiomatizing First-Order Consequences in Dependence Logic. Annals of Pure and Applied Logic 164 (11):1101-1117.
    Dependence logic, introduced in Väänänen [11], cannot be axiomatized. However, first-order consequences of dependence logic sentences can be axiomatized, and this is what we shall do in this paper. We give an explicit axiomatization and prove the respective Completeness Theorem.
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  9. Juha Kontinen, Jouko Väänänen & Dag Westerståhl (2013). Editorial Introduction. Studia Logica 101 (2):233-236.
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  10. Jouko Väänänen & Tong Wang (2013). An Ehrenfeucht‐Fraïssé Game for Lω1ω. Mathematical Logic Quarterly 59 (4-5):357-370.
  11. Jouko Vaananen (2012). Set Theory. Journal of the Indian Council of Philosophical Research 1.
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  12. Jouko Väänänen (2012). Models and Games. Cambridge Studies in Advanced Mathematics, Vol. 132. Bulletin of Symbolic Logic 18 (3):406-408.
     
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  13. Jouko Väänänen (2012). Second Order Logic or Set Theory? Bulletin of Symbolic Logic 18 (1):91-121.
    We try to answer the question which is the “right” foundation of mathematics, second order logic or set theory. Since the former is usually thought of as a formal language and the latter as a first order theory, we have to rephrase the question. We formulate what we call the second order view and a competing set theory view, and then discuss the merits of both views. On the surface these two views seem to be in manifest conflict with each (...)
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  14. Mirna Džamonja & Jouko Väänänen (2011). Chain Models, Trees of Singular Cardinality and Dynamic Ef-Games. Journal of Mathematical Logic 11 (01):61-85.
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  15. Menachem Magidor & Jouko Väänänen (2011). On Löwenheim–Skolem–Tarski Numbers for Extensions of First Order Logic. Journal of Mathematical Logic 11 (01):87-113.
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  16. Jouko Väänänen (2011). A Taste of Set Theory for Philosophers. Journal of the Indian Council of Philosophical Research (2):143-163.
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  17. Jouko Väänänen (2011). Erratum To: On Definability in Dependence Logic. [REVIEW] Journal of Logic, Language and Information 20 (1):133-134.
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  18. Juha Kontinen & Jouko Väänänen (2010). A Remark on Negation in Dependence Logic. Notre Dame Journal of Formal Logic 52 (1):55-65.
    We show that for any pair $\phi$ and $\psi$ of contradictory formulas of dependence logic there is a formula $\theta$ of the same logic such that $\phi\equiv\theta$ and $\psi\equiv\neg\theta$. This generalizes a result of Burgess.
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  19. Jouko Väänänen & Wilfrid Hodges (2010). Dependence of Variables Construed as an Atomic Formula. Annals of Pure and Applied Logic 161 (6):817-828.
    We define a logic capable of expressing dependence of a variable on designated variables only. Thus has similar goals to the Henkin quantifiers of [4] and the independence friendly logic of [6] that it much resembles. The logic achieves these goals by realizing the desired dependence declarations of variables on the level of atomic formulas. By [3] and [17], ability to limit dependence relations between variables leads to existential second order expressive power. Our avoids some difficulties arising in the original (...)
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  20. Jouko Väänänen & Dag Westerståhl (2010). In memoriam: Per Lindström. Theoria 76 (2):100-107.
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  21. Samson Abramsky & Jouko Väänänen (2009). From If to Bi. Synthese 167 (2):207 - 230.
    We take a fresh look at the logics of informational dependence and independence of Hintikka and Sandu and Väänänen, and their compositional semantics due to Hodges. We show how Hodges’ semantics can be seen as a special case of a general construction, which provides a context for a useful completeness theorem with respect to a wider class of models. We shed some new light on each aspect of the logic. We show that the natural propositional logic carried by the semantics (...)
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  22. Barbara F. Csima, Inessa Epstein, Rahim Moosa, Christian Rosendal, Jouko Väänänen & Ali Enayat (2009). Marriott Wardman Park Hotel, Washington, DC January 7–8, 2009. Bulletin of Symbolic Logic 15 (2).
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  23. Juha Kontinen & Jouko Väänänen (2009). On Definability in Dependence Logic. Journal of Logic, Language and Information 18 (3):317-332.
    We study the expressive power of open formulas of dependence logic introduced in Väänänen [Dependence logic (Vol. 70 of London Mathematical Society Student Texts), 2007]. In particular, we answer a question raised by Wilfrid Hodges: how to characterize the sets of teams definable by means of identity only in dependence logic, or equivalently in independence friendly logic.
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  24. S. Barry Cooper, Herman Geuvers, Anand Pillay & Jouko Väänänen (2008). Preface. Annals of Pure and Applied Logic 156 (1):1-2.
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  25. Juliette Kennedy, Saharon Shelah & Jouko Väänänen (2008). Regular Ultrafilters and Finite Square Principles. Journal of Symbolic Logic 73 (3):817-823.
    We show that many singular cardinals λ above a strongly compact cardinal have regular ultrafilters D that violate the finite square principle $\square _{\lambda ,D}^{\mathit{fin}}$ introduced in [3]. For such ultrafilters D and cardinals λ there are models of size λ for which Mλ / D is not λ⁺⁺-universal and elementarily equivalent models M and N of size λ for which Mλ / D and Nλ / D are non-isomorphic. The question of the existence of such ultrafilters and models was (...)
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  26. Jouko Väänänen (2008). The Craig Interpolation Theorem in Abstract Model Theory. Synthese 164 (3):401 - 420.
    The Craig Interpolation Theorem is intimately connected with the emergence of abstract logic and continues to be the driving force of the field. I will argue in this paper that the interpolation property is an important litmus test in abstract model theory for identifying “natural,” robust extensions of first order logic. My argument is supported by the observation that logics which satisfy the interpolation property usually also satisfy a Lindström type maximality theorem. Admittedly, the range of such logics is small.
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  27. Juliette Kennedy & Jouko Vaananen (2007). On Applications of Transfer Principles in Model Theory. In Alessandro Andretta (ed.), On Applications of Transfer Principles in Model Theory. Quaderni di Matematica.
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  28. Saharon Shelah & Jouko Väänänen (2006). Recursive Logic Frames. Mathematical Logic Quarterly 52 (2):151-164.
    We define the concept of a logic frame , which extends the concept of an abstract logic by adding the concept of a syntax and an axiom system. In a recursive logic frame the syntax and the set of axioms are recursively coded. A recursive logic frame is called complete , if every finite consistent theory has a model. We show that for logic frames built from the cardinality quantifiers “there exists at least λ ” completeness always implies .0-compactness. On (...)
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  29. Jouko Väänänen (2006). A Remark on Nondeterminacy in IF Logic. Acta Philosophica Fennica 78 (2006):71-77.
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  30. Rohit Parikh & Jouko Väänänen (2005). Finite Information Logic. Annals of Pure and Applied Logic 134 (1):83-93.
    We introduce a generalization of Independence Friendly logic in which Eloise is restricted to a finite amount of information about Abelard’s moves. This logic is shown to be equivalent to a sublogic of first-order logic, to have the finite model property, and to be decidable. Moreover, it gives an exponential compression relative to logic.
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  31. Saharon Shelah & Jouko Väänänen (2005). A Note on Extensions of Infinitary Logic. Archive for Mathematical Logic 44 (1):63-69.
    We show that a strong form of the so called Lindström’s Theorem [4] fails to generalize to extensions of L κ ω and L κ κ : For weakly compact κ there is no strongest extension of L κ ω with the (κ,κ)-compactness property and the Löwenheim-Skolem theorem down to κ. With an additional set-theoretic assumption, there is no strongest extension of L κ κ with the (κ,κ)-compactness property and the Löwenheim-Skolem theorem down to <κ.
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  32. Jouko Vaananen (2004). Barwise: Abstract Model Theory and Generalized Quantifiers. Bulletin of Symbolic Logic 10 (1):37-53.
  33. Jouko Väänänen (2004). Barwise: Abstract Model Theory and Generalized Quantifiers. Bulletin of Symbolic Logic 10 (1):37-53.
  34. Jouko Väänänen & Boban Veličković (2004). Games Played on Partial Isomorphisms. Archive for Mathematical Logic 43 (1):19-30.
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  35. France Xii, Marcelo Coniglio, Gilles Dowek, Jouko Väänanen, Renata Wassermann, Eric Allender, Jean-Baptiste Joinet & Dale Miller (2004). Ouro Preto (Minas Gerais), Brazil July 29–August 1, 2003. Bulletin of Symbolic Logic 10 (2).
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  36. Jouko Väänänen (2002). On the Semantics of Informational Independence. Logic Journal of the Igpl 10 (3):339-352.
    The semantics of the independence friendly logic of Hintikka and Sandu is usually defined via a game of imperfect information. We give a definition in terms of a game of perfect information. We also give an Ehrenfeucht-Fraïssé game adequate for this logic and use it to define a Distributive Normal Form for independence friendly logic.
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  37. Jouko Väänänen & Dag Westerståhl (2002). On the Expressive Power of Monotone Natural Language Quantifiers Over Finite Models. Journal of Philosophical Logic 31 (4):327-358.
    We study definability in terms of monotone generalized quantifiers satisfying Isomorphism Closure, Conservativity and Extension. Among the quantifiers with the latter three properties - here called CE quantifiers - one finds the interpretations of determiner phrases in natural languages. The property of monotonicity is also linguistically ubiquitous, though some determiners like an even number of are highly non-monotone. They are nevertheless definable in terms of monotone CE quantifiers: we give a necessary and sufficient condition for such definability. We further identify (...)
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  38. Jouko Vaananen (2001). Second-Order Logic and Foundations of Mathematics. Bulletin of Symbolic Logic 7 (4):504-520.
    We discuss the differences between first-order set theory and second-order logic as a foundation for mathematics. We analyse these languages in terms of two levels of formalization. The analysis shows that if second-order logic is understood in its full semantics capable of characterizing categorically central mathematical concepts, it relies entirely on informal reasoning. On the other hand, if it is given a weak semantics, it loses its power in expressing concepts categorically. First-order set theory and second-order logic are not radically (...)
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  39. Saharon Shelah & Jouko Väänänen (2000). Stationary Sets and Infinitary Logic. Journal of Symbolic Logic 65 (3):1311-1320.
    Let K 0 λ be the class of structures $\langle\lambda, , where $A \subseteq \lambda$ is disjoint from a club, and let K 1 λ be the class of structures $\langle\lambda, , where $A \subseteq \lambda$ contains a club. We prove that if $\lambda = \lambda^{ is regular, then no sentence of L λ+κ separates K 0 λ and K 1 λ . On the other hand, we prove that if $\lambda = \mu^+,\mu = \mu^{ , and a forcing axiom (...)
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  40. Jörg Flum, Matthias Schiehlen & Jouko Väänänen (1999). Quantifiers and Congruence Closure. Studia Logica 62 (3):315-340.
    We prove some results about the limitations of the expressive power of quantifiers on finite structures. We define the concept of a bounded quantifier and prove that every relativizing quantifier which is bounded is already first-order definable (Theorem 3.8). We weaken the concept of congruence closed (see [6]) to weakly congruence closed by restricting to congruence relations where all classes have the same size. Adapting the concept of a thin quantifier (Caicedo [1]) to the framework of finite structures, we define (...)
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  41. Stevo Todorčević & Jouko Väänänen (1999). Trees and Ehrenfeucht–Fraı̈ssé Games. Annals of Pure and Applied Logic 100 (1-3):69-97.
    Trees are natural generalizations of ordinals and this is especially apparent when one tries to find an uncountable analogue of the concept of the Scott-rank of a countable structure. The purpose of this paper is to introduce new methods in the study of an ordering between trees whose analogue is the usual ordering between ordinals. For example, one of the methods is the tree-analogue of the successor operation on the ordinals.
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  42. Lauri Hella, Jouko Väänänen & Dag Westerståhl (1997). Definability of Polyadic Lifts of Generalized Quantifiers. Journal of Logic, Language and Information 6 (3):305-335.
    We study generalized quantifiers on finite structures.With every function : we associate a quantifier Q by letting Q x say there are at least (n) elementsx satisfying , where n is the sizeof the universe. This is the general form ofwhat is known as a monotone quantifier of type .We study so called polyadic liftsof such quantifiers. The particular lifts we considerare Ramseyfication, branching and resumption.In each case we get exact criteria fordefinability of the lift in terms of simpler quantifiers.
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  43. Jouko Vaananen (1997). Generalized Quantifiers and Computation, 9th European Summer School in Logic, Language, and Information, ESSLLI'97 Workshop, Aix-En-Provence, France, August 11-22, 1997, Revised Lectures. Springer.
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  44. Jouko Väänänen (1997). Unary Quantifiers on Finite Models. Journal of Logic, Language and Information 6 (3):275-304.
    In this paper (except in Section 5) all quantifiers are assumedto be so called simple unaryquantifiers, and all models are assumedto be finite. We give a necessary and sufficientcondition for a quantifier to be definablein terms of monotone quantifiers. For amonotone quantifier we give a necessaryand sufficient condition for beingdefinable in terms of a given set of bounded monotonequantifiers. Finally, we give a necessaryand sufficient condition for a monotonequantifier to be definable in terms of agiven monotone quantifier.Our analysis shows that (...)
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  45. Lauri Hella, Kerkko Luosto & Jouko Väänänen (1996). The Hierarchy Theorem for Generalized Quantifiers. Journal of Symbolic Logic 61 (3):802-817.
    The concept of a generalized quantifier of a given similarity type was defined in [12]. Our main result says that on finite structures different similarity types give rise to different classes of generalized quantifiers. More exactly, for every similarity type t there is a generalized quantifier of type t which is not definable in the extension of first order logic by all generalized quantifiers of type smaller than t. This was proved for unary similarity types by Per Lindström [17] with (...)
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  46. Phokion G. Kolaitis & Jouko A. Väänänen (1995). Generalized Quantifiers and Pebble Games on Finite Structures. Annals of Pure and Applied Logic 74 (1):23-75.
    First-order logic is known to have a severely limited expressive power on finite structures. As a result, several different extensions have been investigated, including fragments of second-order logic, fixpoint logic, and the infinitary logic L∞ωω in which every formula has only a finite number of variables. In this paper, we study generalized quantifiers in the realm of finite structures and combine them with the infinitary logic L∞ωω to obtain the logics L∞ωω, where Q = {Qi: iε I} is a family (...)
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  47. Jouko Väänänen (1995). Games and Trees in Infinitary Logic: A Survey. In M. Krynicki, M. Mostowski & L. Szczerba (eds.), Quantifiers: Logics, Models and Computation. Kluwer Academic Publishers. 105--138.
  48. Heikki Heikkilä & Jouko Väänänen (1994). Reflection of Long Game Formulas. Mathematical Logic Quarterly 40 (3):381-392.
    We study game formulas the truth of which is determined by a semantical game of uncountable length. The main theme is the study of principles stating reflection of these formulas in various admissible sets. This investigation leads to two weak forms of strict-II11 reflection . We show that admissible sets such as H and Lω2 which fail to have strict-II11 reflection, may or may not, depending on set-theoretic hypotheses satisfy one or both of these weaker forms.
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  49. Alan Mekler & Jouko Väänänen (1993). Trees and Π 1 1 -Subsets of Ω1 Ω 1. Journal of Symbolic Logic 58 (3):1052 - 1070.
    We study descriptive set theory in the space ω1 ω 1 by letting trees with no uncountable branches play a similar role as countable ordinals in traditional descriptive set theory. By using such trees, we get, for example, a covering property for the class of Π 1 1 -sets of ω1 ω 1 . We call a family U of trees universal for a class V of trees if $\mathscr{U} \subseteq \mathscr{V}$ and every tree in V can be order-preservingly mapped (...)
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  50. Alan Mekler & Jouko Vaananen (1993). Trees and $Pi^11$-Subsets of $^{Omega_1}Omega1$. Journal of Symbolic Logic 58 (3):1052-1070.
    We study descriptive set theory in the space $^{\omega_1}\omega_1$ by letting trees with no uncountable branches play a similar role as countable ordinals in traditional descriptive set theory. By using such trees, we get, for example, a covering property for the class of $\Pi^1_1$-sets of $^{\omega_1}\omega_1$. We call a family $\mathscr{U}$ of trees universal for a class $\mathscr{V}$ of trees if $\mathscr{U} \subseteq \mathscr{V}$ and every tree in $\mathscr{V}$ can be order-preservingly mapped into a tree in $\mathscr{U}$. It is well (...)
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