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  1.  1
    Fixed-Point Models for Paradoxical Predicates.Luca Castaldo - 2021 - Australasian Journal of Logic 18 (7):688-723.
    This paper introduces a new kind of fixed-point semantics, filling a gap within approaches to Liar-like paradoxes involving fixed-point models à la Kripke (1975). The four-valued models presented below, (i) unlike the three-valued, consistent fixed-point models defined in Kripke (1975), are able to differentiate between paradoxical and pathological-but-unparadoxical sentences, and (ii) unlike the four-valued, paraconsistent fixed-point models first studied in Visser (1984) and Woodruff (1984), preserve consistency and groundedness of truth.
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  2.  34
    Strong Depth Relevance.Shay Logan - 2021 - Australasian Journal of Logic 18 (6):645-656.
    Relevant logics infamously have the property that they only validate a conditional when some propositional variable is shared between its antecedent and consequent. This property has been strengthened in a variety of ways over the last half-century. Two of the more famous of these strengthenings are the strong variable sharing property and the depth relevance property. In this paper I demonstrate that an appropriate class of relevant logics has a property that might naturally be characterized as the supremum of these (...)
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  3.  59
    On Not Saying What We Shouldn't Have to Say.Shay Logan & Leach-Krouse Graham - 2021 - Australasian Journal of Logic 18 (5):524-568.
    In this paper we introduce a novel way of building arithmetics whose background logic is R. The purpose of doing this is to point in the direction of a novel family of systems that could be candidates for being the infamous R#1/2 that Meyer suggested we look for.
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  4.  8
    Completeness of Pledger’s Modal Logics of One-Sorted Projective and Elliptic Planes.Rob Goldblatt - 2021 - Australasian Journal of Logic 18 (4).
    Ken Pledger devised a one-sorted approach to the incidence relation of plane geometries, using structures that also support models of propositional modal logic. He introduced a modal system 12g that is valid in one-sorted projective planes, proved that it has finitely many non-equivalent modalities, and identified all possible modality patterns of its extensions. One of these extensions 8f is valid in elliptic planes. These results were presented in his 1980 doctoral dissertation, which is reprinted in this issue of the Australasian (...)
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  5.  9
    Some Interrelations Between Geometry and Modal Logic.Ken Pledger - 2021 - Australasian Journal of Logic 18 (4).
    This is a reprinting of Ken Pledger’s PhD thesis, submitted to the University of Warsaw in 1980 with the degree awarded in 1981. It develops a one-sorted approach to the theory of plane geometry, based on the idea that the usually two-sorted theory “can be made one-sorted by keeping careful account of whether the incidence relation is iterated an even or odd number of times”.The one-sorted structures can also serve as Kripke frames for modal logics, and the thesis defines and (...)
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  6.  42
    Evans' Argument and Vague Objects.Graham Priest - 2021 - Australasian Journal of Logic 18 (3).
    In 1978, Gareth Evans published a short and somewhat cryptic article purporting to establish that there are no vague objects. This paper is a commentary on this. Prima facie, the claim that there are no vague objects is clearly false. Mt Everest, for example, has no precise boundaries. And if this is so, there must be something wrong with Evans' argument. In the paper, I discuss what this is, giving a model of vague objects in the process.
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  7.  7
    Strict/Tolerant Logics Built Using Generalized Weak Kleene Logics.Melvin Fitting - 2021 - Australasian Journal of Logic 18 (2).
    This paper continues my work of [9], which showed there was a broad family of many valued logics that have a strict/tolerant counterpart. Here we consider a generalization of weak Kleene three valued logic, instead of the strong version that was background for that earlier work. We explain the intuition behind that generalization, then determine a subclass of strict/tolerant structures in which a generalization of weak Kleene logic produces the same results that the strong Kleene generalization did. This paper provides (...)
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  8.  8
    The Logic of Internal Rational Agent.Yaroslav Petrukhin - 2021 - Australasian Journal of Logic 18 (2).
    In this paper, we introduce a new four-valued logic which may be viewed as a variation on the theme of Kubyshkina and Zaitsev's Logic of Rational Agent textbf{LRA} cite{LRA}. We call our logic $ bf LIRA$. In contrast to textbf{LRA}, it has three designated values instead of one and a different interpretation of truth values, the same as in Zaitsev and Shramko's bi-facial truth logic cite{ZS}. This logic may be useful in a situation when according to an agent's point of (...)
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  9.  61
    From Hilbert Proofs to Consecutions and Back.Tore Fjetland Øgaard - 2021 - Australasian Journal of Logic 18 (2):51-72.
    Restall set forth a "consecution" calculus in his "An Introduction to Substructural Logics." This is a natural deduction type sequent calculus where the structural rules play an important role. This paper looks at different ways of extending Restall's calculus. It is shown that Restall's weak soundness and completeness result with regards to a Hilbert calculus can be extended to a strong one so as to encompass what Restall calls proofs from assumptions. It is also shown how to extend the calculus (...)
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  10.  10
    Immune Logics.Bruno da Re & Damian Szmuc - 2021 - Australasian Journal of Logic 18 (1):29-52.
    This article is concerned with an exploration of a family of systems—called immune logics—that arise from certain dualizations of the well-known family of infectious logics. The distinctive feature of the semantic of infectious logics is the presence of a certain “infectious” semantic value, by which two different though equivalent things are meant. On the one hand, it is meant that these values are zero elements for all the operations in the underlying algebraic structure. On the other hand, it is meant (...)
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  11.  2
    Information Flow In Logics in the Vicinity of BB.Andrew Tedder - 2021 - Australasian Journal of Logic 18 (1):1-24.
    Situation theory, and channel theory in particular, have been used to provide motivational accounts of the ternary relation semantics of relevant, substructural, and various non-classical logics. Among the constraints imposed by channel-theory, we must posit a certain existence criterion for situations which result from the composites of multiple channels (this is used in modeling information flow). In associative non-classical logics, it is relatively easy to show that a certain such condition is met, but the problem is trickier in non-associative logics. (...)
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  12.  3
    Ehrenfeucht-Fraïssé Games Without Identity.Alasdair Urquhart - 2021 - Australasian Journal of Logic 18 (1):25-28.
    This note defines Ehrenfeucht-Fraïssé games where identity is not present in the basic language. The formulation is applied to show that there is no elementary theory in the language of one binary relation that exactly characterizes models in which the relation is the identity relation.
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  13.  29
    Translating Metainferences Into Formulae: Satisfaction Operators and Sequent Calculi.Ariel Jonathan Roffé & Federico Pailos - 2021 - Australasian Journal of Logic 3.
    In this paper, we present a way to translate the metainferences of a mixed metainferential system into formulae of an extended-language system, called its associated σ-system. To do this, the σ-system will contain new operators (one for each standard), called the σ operators, which represent the notions of "belonging to a (given) standard". We first prove, in a model-theoretic way, that these translations preserve (in)validity. That is, that a metainference is valid in the base system if and only if its (...)
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