## Works by Ryo Kashima

11 found
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1. Cut-free sequent calculi for some tense logics.Ryo Kashima - 1994 - Studia Logica 53 (1):119 - 135.

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2. Cut‐Elimination Theorem for the Logic of Constant Domains.Ryo Kashima & Tatsuya Shimura - 1994 - Mathematical Logic Quarterly 40 (2):153-172.
The logic CD is an intermediate logic which exactly corresponds to the Kripke models with constant domains. It is known that the logic CD has a Gentzen-type formulation called LD and rules are replaced by the corresponding intuitionistic rules) and that the cut-elimination theorem does not hold for LD. In this paper we present a modification of LD and prove the cut-elimination theorem for it. Moreover we prove a “weak” version of cut-elimination theorem for LD, saying that all “cuts” except (...)

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3. Substructural implicational logics including the relevant logic E.Ryo Kashima & Norihiro Kamide - 1999 - Studia Logica 63 (2):181-212.
We introduce several restricted versions of the structural rules in the implicational fragment of Gentzen's sequent calculus LJ. For example, we permit the applications of a structural rule only if its principal formula is an implication. We investigate cut-eliminability and theorem-equivalence among various combinations of them. The results include new cut-elimination theorems for the implicational fragments of the following logics: relevant logic E, strict implication S4, and their neighbors (e.g., E-W and S4-W); BCI-logic, BCK-logic, relevant logic R, and the intuitionistic (...)

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4. On semilattice relevant logics.Ryo Kashima - 2003 - Mathematical Logic Quarterly 49 (4):401.
The semilattice relevant logics ∪R, ∪T, ∪RW, and ∪TW are defined by semilattice models in which conjunction and disjunction are interpreted in a natural way. For each of them, there is a cut-free labelled sequent calculus with plural succedents . We prove that these systems are equivalent, with respect to provable formulas, to the restricted systems with single succedents . Moreover, using this equivalence, we give a new Hilbert-style axiomatizations for ∪R and ∪T and prove equivalence between two semantics for (...)

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5. Sequent Calculi for Visser's Propositional Logics.Kentaro Kikuchi & Ryo Kashima - 2001 - Notre Dame Journal of Formal Logic 42 (1):1-22.
This paper introduces sequent systems for Visser's two propositional logics: Basic Propositional Logic (BPL) and Formal Propositional Logic (FPL). It is shown through semantical completeness that the cut rule is admissible in each system. The relationships with Hilbert-style axiomatizations and with other sequent formulations are discussed. The cut-elimination theorems are also demonstrated by syntactical methods.

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6. Contraction-elimination for implicational logics.Ryo Kashima - 1997 - Annals of Pure and Applied Logic 84 (1):17-39.
We establish the “contraction-elimination theorem” which means that if a sequent Γ A is provable in the implicational fragment of the Gentzen's sequent calculus LK and if it satisfies a certain condition on the number of the occurrences of propositional variables, then it is provable without the right contraction rule. By this theorem, we get the following.1. If an implicational formula A is a theorem of classical logic and is not a theorem of intuitionistic logic, then there is a propositional (...)

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7. Reduction Rules for Intuitionistic $${{\lambda}{\rho}}$$ λ ρ -calculus.Ken-Etsu Fujita, Ryo Kashima, Yuichi Komori & Naosuke Matsuda - 2015 - Studia Logica 103 (6):1225-1244.
The third author gave a natural deduction style proof system called the \-calculus for implicational fragment of classical logic in. In -calculus, 2015, Post-proceedings of the RIMS Workshop “Proof Theory, Computability Theory and Related Issues”, to appear), the fourth author gave a natural subsystem “intuitionistic \-calculus” of the \-calculus, and showed the system corresponds to intuitionistic logic. The proof is given with tree sequent calculus, but is complicated. In this paper, we introduce some reduction rules for the \-calculus, and give (...)

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8. Term-Space Semantics of Typed Lambda Calculus.Ryo Kashima, Naosuke Matsuda & Takao Yuyama - 2020 - Notre Dame Journal of Formal Logic 61 (4):591-600.
Barendregt gave a sound semantics of the simple type assignment system λ → by generalizing Tait’s proof of the strong normalization theorem. In this paper, we aim to extend the semantics so that the completeness theorem holds.

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9. On the completeness and the decidability of strictly monadic second‐order logic.Kento Takagi & Ryo Kashima - 2020 - Mathematical Logic Quarterly 66 (4):438-447.
Regarding strictly monadic second‐order logic (SMSOL), which is the fragment of monadic second‐order logic in which all predicate constants are unary and there are no function symbols, we show that a standard deductive system with full comprehension is sound and complete with respect to standard semantics. This result is achieved by showing that in the case of SMSOL, the truth value of any formula in a faithful identity‐standard Henkin structure is preserved when the structure is “standardized”; that is, the predicate (...)
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10. On the Difficulty of Writing Out formal Proofs in Arithmetic.Ryo Kashima & Takeshi Yamaguchi - 1997 - Mathematical Logic Quarterly 43 (3):328-332.
Let ℸ be the set of Gödel numbers Gn of function symbols f such that PRA ⊢ and let γ be the function such that equation imageWe prove: The r. e. set ℸ is m-complete; the function γ is not primitive recursive in any class of functions {f1, f2, ⃛} so long as each fi has a recursive upper bound. This implies that γ is not primitive recursive in ℸ although it is recursive in ℸ.