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  1. Definable Well-Orders of $H(\Omega _2)$ and $GCH$.David Asperó & Sy-David Friedman - 2012 - Journal of Symbolic Logic 77 (4):1101-1121.
    Assuming ${2^{{N_0}}}$ = N₁ and ${2^{{N_1}}}$ = N₂, we build a partial order that forces the existence of a well-order of H(ω₂) lightface definable over ⟨H(ω₂), Є⟩ and that preserves cardinal exponentiation and cofinalities.
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  2.  54
    The Search for New Axioms in the Hyperuniverse Programme.Claudio Ternullo & Sy-David Friedman - 2016 - In Andrea Sereni & Francesca Boccuni (eds.), Objectivity, Realism and Proof (FilMat Studies in the Philosophy of Mathematics). Berlin: Springer. pp. 165-188.
    The Hyperuniverse Programme, introduced in Arrigoni and Friedman (2013), fosters the search for new set-theoretic axioms. In this paper, we present the procedure envisaged by the programme to find new axioms and the conceptual framework behind it. The procedure comes in several steps. Intrinsically motivated axioms are those statements which are suggested by the standard concept of set, i.e. the `maximal iterative concept', and the programme identi fies higher-order statements motivated by the maximal iterative concept. The satisfaction of these statements (...)
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  3.  2
    On Strong Forms of Reflection in Set Theory.Sy-David Friedman & Radek Honzik - 2016 - Mathematical Logic Quarterly 62 (1-2):52-58.
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  4.  13
    Slow Consistency.Sy-David Friedman, Michael Rathjen & Andreas Weiermann - 2013 - Annals of Pure and Applied Logic 164 (3):382-393.
    The fact that “natural” theories, i.e. theories which have something like an “idea” to them, are almost always linearly ordered with regard to logical strength has been called one of the great mysteries of the foundation of mathematics. However, one easily establishes the existence of theories with incomparable logical strengths using self-reference . As a result, PA+Con is not the least theory whose strength is greater than that of PA. But still we can ask: is there a sense in which (...)
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  5.  9
    Rank-Into-Rank Hypotheses and the Failure of GCH.Vincenzo Dimonte & Sy-David Friedman - 2014 - Archive for Mathematical Logic 53 (3-4):351-366.
  6.  3
    Large Cardinals and Locally Defined Well-Orders of the Universe.David Asperó & Sy-David Friedman - 2009 - Annals of Pure and Applied Logic 157 (1):1-15.
    By forcing over a model of with a class-sized partial order preserving this theory we produce a model in which there is a locally defined well-order of the universe; that is, one whose restriction to all levels H is a well-order of H definable over the structure H, by a parameter-free formula. Further, this forcing construction preserves all supercompact cardinals as well as all instances of regular local supercompactness. It is also possible to define variants of this construction which, in (...)
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  7.  18
    Fusion and Large Cardinal Preservation.Sy-David Friedman, Radek Honzik & Lyubomyr Zdomskyy - 2013 - Annals of Pure and Applied Logic 164 (12):1247-1273.
    In this paper we introduce some fusion properties of forcing notions which guarantee that an iteration with supports of size ⩽κ not only does not collapse κ+ but also preserves the strength of κ . This provides a general theory covering the known cases of tree iterations which preserve large cardinals [3], Friedman and Halilović [5], Friedman and Honzik [6], Friedman and Magidor [8], Friedman and Zdomskyy [10], Honzik [12]).
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  8.  7
    Perfect Trees and Elementary Embeddings.Sy-David Friedman & Katherine Thompson - 2008 - Journal of Symbolic Logic 73 (3):906-918.
    An important technique in large cardinal set theory is that of extending an elementary embedding j: M → N between inner models to an elementary embedding j*: M[G] → N[G*] between generic extensions of them. This technique is crucial both in the study of large cardinal preservation and of internal consistency. In easy cases, such as when forcing to make the GCH hold while preserving a measurable cardinal (via a reverse Easton iteration of α-Cohen forcing for successor cardinals α), the (...)
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  9.  1
    Fusion and Large Cardinal Preservation.Sy-David Friedman, Radek Honzik & Lyubomyr Zdomskyy - 2013 - Annals of Pure and Applied Logic 164 (12):1247-1273.
    In this paper we introduce some fusion properties of forcing notions which guarantee that an iteration with supports of size ⩽κ not only does not collapse κ+ but also preserves the strength of κ. This provides a general theory covering the known cases of tree iterations which preserve large cardinals [3], Friedman and Halilović [5], Friedman and Honzik [6], Friedman and Magidor [8], Friedman and Zdomskyy [10], Honzik [12]).
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  10.  22
    Internal Consistency and the Inner Model Hypothesis.Sy-David Friedman - 2006 - Bulletin of Symbolic Logic 12 (4):591-600.
  11.  3
    Easton’s Theorem and Large Cardinals.Sy-David Friedman & Radek Honzik - 2008 - Annals of Pure and Applied Logic 154 (3):191-208.
    The continuum function αmaps to2α on regular cardinals is known to have great freedom. Let us say that F is an Easton function iff for regular cardinals α and β, image and α<β→F≤F. The classic example of an Easton function is the continuum function αmaps to2α on regular cardinals. If GCH holds then any Easton function is the continuum function on regular cardinals of some cofinality-preserving extension V[G]; we say that F is realised in V[G]. However if we also wish (...)
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  12.  19
    Isomorphism Relations on Computable Structures.Ekaterina B. Fokina, Sy-David Friedman, Valentina Harizanov, Julia F. Knight, Charles McCoy & Antonio Montalbán - 2012 - Journal of Symbolic Logic 77 (1):122-132.
    We study the complexity of the isomorphism relation on classes of computable structures. We use the notion of FF-reducibility introduced in [9] to show completeness of the isomorphism relation on many familiar classes in the context of all ${\mathrm{\Sigma }}_{1}^{1}$ equivalence relations on hyperarithmetical subsets of ω.
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  13.  4
    The Tree Property at the ℵ 2 N 's and the Failure of SCH at ℵ Ω.Sy-David Friedman & Radek Honzik - 2015 - Annals of Pure and Applied Logic 166 (4):526-552.
  14.  4
    Large Cardinals and Definable Well-Orders, Without the GCH.Sy-David Friedman & Philipp Lücke - 2015 - Annals of Pure and Applied Logic 166 (3):306-324.
  15.  8
    The Effective Theory of Borel Equivalence Relations.Ekaterina B. Fokina, Sy-David Friedman & Asger Törnquist - 2010 - Annals of Pure and Applied Logic 161 (7):837-850.
    The study of Borel equivalence relations under Borel reducibility has developed into an important area of descriptive set theory. The dichotomies of Silver [20] and Harrington, Kechris and Louveau [6] show that with respect to Borel reducibility, any Borel equivalence relation strictly above equality on ω is above equality on , the power set of ω, and any Borel equivalence relation strictly above equality on the reals is above equality modulo finite on . In this article we examine the effective (...)
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  16.  20
    The Number of Normal Measures.Sy-David Friedman & Menachem Magidor - 2009 - Journal of Symbolic Logic 74 (3):1069-1080.
    There have been numerous results showing that a measurable cardinal κ can carry exactly α normal measures in a model of GCH, where a is a cardinal at most κ⁺⁺. Starting with just one measurable cardinal, we have [9] (for α = 1), [10] (for α = κ⁺⁺, the maximum possible) and [1] (for α = κ⁺, after collapsing κ⁺⁺) . In addition, under stronger large cardinal hypotheses, one can handle the remaining cases: [12] (starting with a measurable cardinal of (...)
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  17.  1
    The Tree Property at א Ω+2.Sy-David Friedman & Ajdin Halilović - 2011 - Journal of Symbolic Logic 76 (2):477 - 490.
    Assuming the existence of a weakly compact hypermeasurable cardinal we prove that in some forcing extension א ω is a strong limit cardinal and א ω+2 has the tree property. This improves a result of Matthew Foreman (see [2]).
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  18.  46
    On the Consistency Strength of the Inner Model Hypothesis.Sy-David Friedman, Philip Welch & W. Hugh Woodin - 2008 - Journal of Symbolic Logic 73 (2):391 - 400.
  19.  62
    Multiverse Conceptions in Set Theory.Carolin Antos, Sy-David Friedman, Radek Honzik & Claudio Ternullo - 2015 - Synthese 192 (8):2463-2488.
    We review different conceptions of the set-theoretic multiverse and evaluate their features and strengths. In Sect. 1, we set the stage by briefly discussing the opposition between the ‘universe view’ and the ‘multiverse view’. Furthermore, we propose to classify multiverse conceptions in terms of their adherence to some form of mathematical realism. In Sect. 2, we use this classification to review four major conceptions. Finally, in Sect. 3, we focus on the distinction between actualism and potentialism with regard to the (...)
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  20.  67
    The Hyperuniverse Program.Tatiana Arrigoni & Sy-David Friedman - 2013 - Bulletin of Symbolic Logic 19 (1):77-96.
    The Hyperuniverse Program is a new approach to set-theoretic truth which is based on justifiable principles and leads to the resolution of many questions independent from ZFC. The purpose of this paper is to present this program, to illustrate its mathematical content and implications, and to discuss its philosophical assumptions.
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  21.  6
    Homogeneous Iteration and Measure One Covering Relative to HOD.Natasha Dobrinen & Sy-David Friedman - 2008 - Archive for Mathematical Logic 47 (7-8):711-718.
    Relative to a hyperstrong cardinal, it is consistent that measure one covering fails relative to HOD. In fact it is consistent that there is a superstrong cardinal and for every regular cardinal κ, κ + is greater than κ + of HOD. The proof uses a very general lemma showing that homogeneity is preserved through certain reverse Easton iterations.
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  22.  23
    Projective Mad Families.Sy-David Friedman & Lyubomyr Zdomskyy - 2010 - Annals of Pure and Applied Logic 161 (12):1581-1587.
    Using almost disjoint coding we prove the consistency of the existence of a definable ω-mad family of infinite subsets of ω together with.
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  23.  16
    Large Cardinals Need Not Be Large in HOD.Yong Cheng, Sy-David Friedman & Joel David Hamkins - 2015 - Annals of Pure and Applied Logic 166 (11):1186-1198.
  24.  4
    Set Theory and Structures.Neil Barton & Sy-David Friedman - unknown
    Set-theoretic and category-theoretic foundations represent different perspectives on mathematical subject matter. In particular, category-theoretic language focusses on properties that can be determined up to isomorphism within a category, whereas set theory admits of properties determined by the internal structure of the membership relation. Various objections have been raised against this aspect of set theory in the category-theoretic literature. In this article, we advocate a methodological pluralism concerning the two foundational languages, and provide a theory that fruitfully interrelates a `structural' perspective (...)
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  25.  1
    Safe Recursive Set Functions.Arnold Beckmann, Samuel R. Buss & Sy-David Friedman - 2015 - Journal of Symbolic Logic 80 (3):730-762.
  26.  1
    Analytic Equivalence Relations and Bi-Embeddability.Friedman Sy-David & Ros Luca Motto - 2011 - Journal of Symbolic Logic 76 (1):243 - 266.
    Louveau and Rosendal [5] have shown that the relation of bi-embeddability for countable graphs as well as for many other natural classes of countable structures is complete under Borel reducibility for analytic equivalence relations. This is in strong contrast to the case of the isomorphism relation, which as an equivalence relation on graphs (or on any class of countable structures consisting of the models of a sentence of L ω ₁ ω ) is far from complete (see [5, 2]). In (...)
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  27. Analytic Equivalence Relations and Bi-Embeddability.Sy-David Friedman & Luca Ros - 2011 - Journal of Symbolic Logic 76 (1):243-266.
    Louveau and Rosendal [5] have shown that the relation of bi-embeddability for countable graphs as well as for many other natural classes of countable structures is complete under Borel reducibility for analytic equivalence relations. This is in strong contrast to the case of the isomorphism relation, which as an equivalence relation on graphs is far from complete.In this article we strengthen the results of [5] by showing that not only does bi-embeddability give rise to analytic equivalence relations which are complete (...)
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  28.  2
    A Model of Second-Order Arithmetic Satisfying AC but Not DC.Sy-David Friedman, Victoria Gitman & Vladimir Kanovei - forthcoming - Journal of Mathematical Logic:1850013.
    We show that there is a β-model of second-order arithmetic in which the choice scheme holds, but the dependent choice scheme fails for a Π21-assertion, confirming a conjecture of Stephen Simpson. We obtain as a corollary that the Reflection Principle, stating that every formula reflects to a transitive set, can fail in models of ZFC−. This work is a rediscovery by the first two authors of a result obtained by the third author in [V. G. Kanovei, On descriptive forms of (...)
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  29.  24
    Foundational Implications of the Inner Model Hypothesis.Tatiana Arrigoni & Sy-David Friedman - 2012 - Annals of Pure and Applied Logic 163 (10):1360-1366.
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  30.  24
    On Borel Equivalence Relations in Generalized Baire Space.Sy-David Friedman & Tapani Hyttinen - 2012 - Archive for Mathematical Logic 51 (3-4):299-304.
    We construct two Borel equivalence relations on the generalized Baire space κ κ , κ <κ = κ > ω, with the property that neither of them is Borel reducible to the other. A small modification of the construction shows that the straightforward generalization of the Glimm-Effros dichotomy fails.
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  31.  1
    Large Cardinals and Gap-1 Morasses.Andrew D. Brooke-Taylor & Sy-David Friedman - 2009 - Annals of Pure and Applied Logic 159 (1-2):71-99.
    We present a new partial order for directly forcing morasses to exist that enjoys a significant homogeneity property. We then use this forcing in a reverse Easton iteration to obtain an extension universe with morasses at every regular uncountable cardinal, while preserving all n-superstrong , hyperstrong and 1-extendible cardinals. In the latter case, a preliminary forcing to make the GCH hold is required. Our forcing yields morasses that satisfy an extra property related to the homogeneity of the partial order; we (...)
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  32.  12
    The Stable Core.Sy-David Friedman - 2012 - Bulletin of Symbolic Logic 18 (2):261-267.
    Vopenka [2] proved long ago that every set of ordinals is set-generic over HOD, Gödel's inner model of hereditarily ordinal-definable sets. Here we show that the entire universe V is class-generic over, and indeed over the even smaller inner model $\mathbb{S}=$, where S is the Stability predicate. We refer to the inner model $\mathbb{S}$ as the Stable Core of V. The predicate S has a simple definition which is more absolute than any definition of HOD; in particular, it is possible (...)
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  33.  24
    Strong Isomorphism Reductions in Complexity Theory.Sam Buss, Yijia Chen, Jörg Flum, Sy-David Friedman & Moritz Müller - 2011 - Journal of Symbolic Logic 76 (4):1381-1402.
    We give the first systematic study of strong isomorphism reductions, a notion of reduction more appropriate than polynomial time reduction when, for example, comparing the computational complexity of the isomorphim problem for different classes of structures. We show that the partial ordering of its degrees is quite rich. We analyze its relationship to a further type of reduction between classes of structures based on purely comparing for every n the number of nonisomorphic structures of cardinality at most n in both (...)
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  34.  7
    Co-Stationarity of the Ground Model.Natasha Dobrinen & Sy-David Friedman - 2006 - Journal of Symbolic Logic 71 (3):1029 - 1043.
    This paper investigates when it is possible for a partial ordering P to force Pκ(λ) \ V to be stationary in VP. It follows from a result of Gitik that whenever P adds a new real, then Pκ(λ) \ V is stationary in VP for each regular uncountable cardinal κ in VP and all cardinals λ > κ in VP [4]. However, a covering theorem of Magidor implies that when no new ω-sequences are added, large cardinals become necessary [7]. The (...)
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  35.  7
    Hypermachines.Sy-David Friedman & P. D. Welch - 2011 - Journal of Symbolic Logic 76 (2):620 - 636.
    The Infinite Time Turing Machine model [8] of Hamkins and Kidder is, in an essential sense, a "Σ₂-machine" in that it uses a Σ₂ Liminf Rule to determine cell values at limit stages of time. We give a generalisation of these machines with an appropriate Σ n rule. Such machines either halt or enter an infinite loop by stage ζ(n) = df μζ(n)[∃Σ(n) > ζ(n) L ζ(n) ≺ Σn L Σ(n) ], again generalising precisely the ITTM case. The collection of (...)
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  36.  2
    The Eightfold Way.James Cummings, Sy-David Friedman, Menachem Magidor, Assaf Rinot & Dima Sinapova - 2018 - Journal of Symbolic Logic 83 (1):349-371.
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  37.  21
    Independence of Higher Kurepa Hypotheses.Sy-David Friedman & Mohammad Golshani - 2012 - Archive for Mathematical Logic 51 (5-6):621-633.
    We study the Generalized Kurepa hypothesis introduced by Chang. We show that relative to the existence of an inaccessible cardinal the Gap-n-Kurepa hypothesis does not follow from the Gap-m-Kurepa hypothesis for m different from n. The use of an inaccessible is necessary for this result.
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  38.  8
    Maximality and Ontology: How Axiom Content Varies Across Philosophical Frameworks.Neil Barton & Sy-David Friedman - 2017 - Synthese:1-27.
    Discussion of new axioms for set theory has often focused on conceptions of maximality, and how these might relate to the iterative conception of set. This paper provides critical appraisal of how certain maximality axioms behave on different conceptions of ontology concerning the iterative conception. In particular, we argue that forms of multiversism and actualism face complementary problems. The latter view is unable to use maximality axioms that make use of extensions, where the former has to contend with the existence (...)
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  39.  18
    Hyperfine Structure Theory and Gap 1 Morasses.Sy-David Friedman, Peter Koepke & Boris Piwinger - 2006 - Journal of Symbolic Logic 71 (2):480 - 490.
    Using the Friedman-Koepke Hyperfine Structure Theory of [2], we provide a short construction of a gap 1 morass in the constructible universe.
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  40.  2
    The Tree Property at the Double Successor of a Singular Cardinal with a Larger Gap.Sy-David Friedman, Radek Honzik & Šárka Stejskalová - 2018 - Annals of Pure and Applied Logic 169 (6):548-564.
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  41.  17
    Eastonʼs Theorem and Large Cardinals From the Optimal Hypothesis.Sy-David Friedman & Radek Honzik - 2012 - Annals of Pure and Applied Logic 163 (12):1738-1747.
    The equiconsistency of a measurable cardinal with Mitchell order o=κ++ with a measurable cardinal such that 2κ=κ++ follows from the results by W. Mitchell [13] and M. Gitik [7]. These results were later generalized to measurable cardinals with 2κ larger than κ++ .In Friedman and Honzik [5], we formulated and proved Eastonʼs theorem [4] in a large cardinal setting, using slightly stronger hypotheses than the lower bounds identified by Mitchell and Gitik , for a suitable μ, instead of the cardinals (...)
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  42.  4
    Hyperclass Forcing in Morse-Kelley Class Theory.Carolin Antos & Sy-David Friedman - 2017 - Journal of Symbolic Logic 82 (2):549-575.
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  43.  14
    On Absoluteness of Categoricity in Abstract Elementary Classes.Sy-David Friedman & Martin Koerwien - 2011 - Notre Dame Journal of Formal Logic 52 (4):395-402.
    Shelah has shown that $\aleph_1$-categoricity for Abstract Elementary Classes (AECs) is not absolute in the following sense: There is an example $K$ of an AEC (which is actually axiomatizable in the logic $L(Q)$) such that if $2^{\aleph_0}.
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  44.  6
    Potential Isomorphism of Elementary Substructures of a Strictly Stable Homogeneous Model.Sy-David Friedman, Tapani Hyttinen & Agatha C. Walczak-Typke - 2011 - Journal of Symbolic Logic 76 (3):987 - 1004.
    The results herein form part of a larger project to characterize the classification properties of the class of submodels of a homogeneous stable diagram in terms of the solvability (in the sense of [1]) of the potential isomorphism problem for this class of submodels. We restrict ourselves to locally saturated submodels of the monster model m of some power π. We assume that in Gödel's constructible universe , π is a regular cardinal at least the successor of the first cardinal (...)
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  45.  4
    Large Cardinals and Lightface Definable Well-Orders, Without the Gch.Sy-David Friedman, Peter Holy & Philipp Lücke - 2015 - Journal of Symbolic Logic 80 (1):251-284.
  46.  13
    □ On the Singular Cardinals.James Cummings & Sy-David Friedman - 2008 - Journal of Symbolic Logic 73 (4):1307-1314.
    We give upper and lower bounds for the consistency strength of the failure of a combinatorial principle introduced by Jensen. "Square on singular cardinals".
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  47.  5
    Definable Normal Measures.Sy-David Friedman & Liuzhen Wu - 2015 - Annals of Pure and Applied Logic 166 (1):46-60.
  48.  1
    Fragments of Kripke–Platek Set Theory and the Metamathematics of $$\Alpha $$ Α -Recursion Theory.Sy-David Friedman, Wei Li & Tin Lok Wong - 2016 - Archive for Mathematical Logic 55 (7-8):899-924.
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  49.  4
    Baumgartnerʼs Conjecture and Bounded Forcing Axioms.David Asperó, Sy-David Friedman, Miguel Angel Mota & Marcin Sabok - 2013 - Annals of Pure and Applied Logic 164 (12):1178-1186.
  50.  3
    Cobham Recursive Set Functions.Arnold Beckmann, Sam Buss, Sy-David Friedman, Moritz Müller & Neil Thapen - 2016 - Annals of Pure and Applied Logic 167 (3):335-369.
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