Classically, weak König's lemma and Brouwer's fan theorem for detachable bars are equivalent. We give a direct constructive proof that the former implies the latter.

精神障害の分類と診断が難しいなか、哲学や精神医学は精神障害とどのように向きあうのか。思考吹入や妄想についての哲学的考察に加え、現象学的精神病理学や精神分析の現状、そして現代の精神医学のさまざまなアプロ ーチの到達点を総観する。.

二十世紀初頭、フッサールによって創唱された現象学。経験のなかに知識の原理として機能する原型を探るこの学問は、ハイデガー、サルトル、メルロ=ポンティらに多大な影響を与え、思想・哲学の大きな潮流となる。フ ッサールの哲学を原テクストに則して問い直し、現象学の基本的事象とその本質を解明する、斯界の泰斗の精緻な思索が結晶した珠玉の書。.

独自の視点から思想の可能性をつかみ出し、現代の倫理として編み直す。鶴見哲学の中心へ、気鋭の哲学者による決定的論考。.

儒教が「国教」となったのはいつか。皇帝と天子は同じものか。曹操はなぜ文学を称揚したか。諸葛亮は何を守ろうとしたのか。「竹林の七賢」は何に抵抗したか。国家の正統性を主張し、統治制度や世界観の裏づけとなる 「正統思想」の意置に儒教が上り、その思想内容が変転していく様を、体系性と神秘思想の鄭玄、合理性と現実主義の王粛、光武帝、王莽、曹操や諸葛亮など、多彩な人物を軸にして、「漢」の成立と衰退、三国、魏晉時代 の歴史を交えながら描き出す。.

In this essay I present the philosophy of Nishida Kitarō, the father of the Kyoto School tradition, as an alternative version of transcendental philosophy. While following the steps of Kant and Husserl in important ways, Nishida attempts to take the transcendental approach even further, finally leaving us with a different view of reality that is neither realist nor idealist, but, rather, radically realist. I call this radical transcendental position, “awakened realism”. Due to word limitations, I can only set the stage (...) for further discussion on what kind of implication this may have for transcendental philosophy. But if I succeed in making my presentation clear enough, it should naturally ignite discussion on how far we can radicalize transcendental philosophy without making it into something else. (shrink)

京都学派の経済哲学者として知られた梯明秀の本格的研究書。梯の戦時下における哲学の再評価と創造的復権をめざして、形而上学批判と根源的自然の復権というまったく新たな視点からその意義と射程を明らかにしようと する力作。.

In this paper, we introduce systems of nonstandard second-order arithmetic which are conservative extensions of systems of second-order arithmetic. Within these systems, we do reverse mathematics for nonstandard analysis, and we can import techniques of nonstandard analysis into analysis in weak systems of second-order arithmetic. Then, we apply nonstandard techniques to a version of Riemannʼs mapping theorem, and show several different versions of Riemannʼs mapping theorem.

Modern technology has radically altered the conditions for human action, endowing us with tremendous power to affect the future. Patterns of action that appear positive in their short-term effects must sometimes be judged unsustainable. Hans Jonas and Thomas Berry are among those who emphasize the necessity of transforming ethics in light of these considerations. In a Whiteheadian framework, this needed transformation is rooted in the nature of things.

The aim of this paper is to examine the role of imagination in environmental ethics and introduce an imaginative dimension as an essential part of environmental ethics. Imagination constitutes a basic condition for ethical thinking and action. Matters of environmental ethics have revealed the indispensable role of imagination in ethics. I’ll advance an imagination-based environmental ethics by developing Hans Jonas’ ethical thought. From his viewpoint, various effects of our action on nature and future generations, generally out of our sight, have (...) become an ethical concern. This necessitates the exercise of imagination because we must “imagine” those distant effects to act in an environmentally responsible way. Jonas’ “heuristics of fear” is an imaginative approach necessary for responsible action. Further, I reinterpret the role of imagination as motivating our “will to know.” In conclusion, I suggest the importance of environmental education as cultivating ecological imagination from the standpoint of environmental ethics. (shrink)

We define a new theory of concatenation WTC which is much weaker than Grzegorczyk's well-known theory TC. We prove that WTC is mutually interpretable with the weak theory of arithmetic R. The latter is, in a technical sense, much weaker than Robinson's arithmetic Q, but still essentially undecidable. Hence, as a corollary, WTC is also essentially undecidable.

The Dedekind cuts in an ordered set form a set in the sense of constructive Zermelo—Fraenkel set theory. We deduce this statement from the principle of refinement, which we distill before from the axiom of fullness. Together with exponentiation, refinement is equivalent to fullness. None of the defining properties of an ordering is needed, and only refinement for two—element coverings is used. In particular, the Dedekind reals form a set; whence we have also refined an earlier result by Aczel and (...) Rathjen, who invoked the full form of fullness. To further generalise this, we look at Richman's method to complete an arbitrary metric space without sequences, which he designed to avoid countable choice. The completion of a separable metric space turns out to be a set even if the original space is a proper class; in particular, every complete separable metric space automatically is a set. (shrink)

Working in the weakening of constructive Zermelo-Fraenkel set theory in which the subset collection scheme is omitted, we show that the binary refinement principle implies all the instances of the exponentiation axiom in which the basis is a discrete set. In particular binary refinement implies that the class of detachable subsets of a set form a set. Binary refinement was originally extracted from the fullness axiom, an equivalent of subset collection, as a principle that was sufficient to prove that the (...) Dedekind reals form a set. Here we show that the Cauchy reals also form a set. More generally, binary refinement ensures that one remains in the realm of sets when one starts from discrete sets and one applies the operations of exponentiation and binary product a finite number of times. (shrink)

Specification acquisition in the system design process has been improved since the middle of the 1980s when the upper CASE tools appeared. On the contrary the quality of requirement acquisition in the upper processes of system design has not been enhanced as much as specification acquisition. Understanding the user's requirements is indispensable as one of the basic conditions for building systems that can really satisfy users.This article discusses obtaining requirement knowledge, in terms of human-centred design. The focus is on the (...) process of requirement acquisition, where there is room for one to make full use of human knowledge in a dynamic manner. (shrink)

It is proved that $\Pi^1_1$ -indescribability in $P_{\kappa}\lambda$ can be characterized by combinatorial properties without taking care of cofinality of $\lambda$ . We extend Carr's theorem proving that the hypothesis $\kappa$ is $2^{\lambda^{<\kappa}}$ -Shelah is rather stronger than $\kappa$ is $\lambda$ -supercompact.

We pursue the idea that predicate logic is a “fibred algebra” while propositional logic is a single algebra; in the context of intuitionism, this algebraic understanding of predicate logic goes back to Lawvere, in particular his concept of hyperdoctrine. Here, we aim at demonstrating that the notion of monad-relativised hyperdoctrines, which are what we call fibred algebras, yields algebraisations of a wide variety of predicate logics. More specifically, we discuss a typed, first-order version of the non-commutative Full Lambek calculus, which (...) has extensively been studied in the past few decades, functioning as a unifying language for different sorts of logical systems (classical, intuitionistic, linear, fuzzy, relevant, etc.). Through the concept of Full Lambek hyperdoctrines, we establish both generic and set-theoretical completeness results for any extension of the base system; the latter arises from a dual adjunction, and is relevant to the tripos-to-topos construction and quantale-valued sets. Furthermore, we give a hyperdoctrinal account of Girard’s and Gödel’s translation. (shrink)

We present statements equivalent to some fragments of the principle of non-deterministic inductive definitions (NID) by van den Berg (2013), working in a weak subsystem of constructive set theory CZF. We show that several statements in constructive topology which were initially proved using NID are equivalent to the elementary and finitary NIDs. We also show that the finitary NID is equivalent to its binary fragment and that the elementary NID is equivalent to a variant of NID based on the notion (...) of biclosed subset. Our result suggests that proving these statements in constructive topology requires genuine extensions of CZF with the elementary or finitary NID. (shrink)

The purpose of this paper is an axiomatic study of the interrelations between certain continuity properties. We deal with principles which are equivalent to the statements "every mapping is sequentially nondiscontinuous", "every sequentially nondiscontinuous mapping is sequentially continuous", and "every sequentially continuous mapping is continuous". As corollaries, we show that every mapping of a complete separable space is continuous in constructive recursive mathematics (the Kreisel-Lacombe-Schoenfield-Tsejtin theorem) and in intuitionism.

We will overview the results in an informal approach to constructive reverse mathematics, that is reverse mathematics in Bishop’s constructive mathematics, especially focusing on compactness properties and continuous properties.

Abstract.A type of subtlety for Pκλ called “strongly subtle” is introduced to show almost ineffability is consistencywise stronger than Shelah property. The following are also shown: is strongly subtle” has rather strong consequences. (ii) The ideal is not strongly subtle} is not λ-saturated, and completely ineffable ideal is not precipitous. (iii) In case that λ<κ=2λ, almost λ-ineffability coincides with λ-ineffability. (iv) It is not provable that κ is λ<κ-ineffable whenever κ is λ-ineffable.

We will overview the results in an informal approach to constructive reverse mathematics, that is reverse mathematics in Bishop’s constructive mathematics, especially focusing on compactness properties and continuous properties.

Inspired by locale theory, we propose “pointfree convex geometry”. We introduce the notion of convexity algebra as a pointfree convexity space. There are two notions of a point for convexity algebra: one is a chain-prime meet-complete filter and the other is a maximal meet-complete filter. In this paper we show the following: the former notion of a point induces a dual equivalence between the category of “spatial” convexity algebras and the category of “sober” convexity spaces as well as a dual (...) adjunction between the category of convexity algebras and the category of convexity spaces; the latter notion of point induces a dual equivalence between the category of “m-spatial” convexity algebras and the category of “m-sober” convexity spaces. We finally argue that the former notion of a point is more useful than the latter one from a category theoretic point of view and that the former notion of a point actually represents a polytope and the latter notion of a point properly represents a point. We also remark on the close relationships between pointfree convex geometry and domain theory. (shrink)

Science does not exist in vacuum; it arises and works in context. Ground-breaking achievements transforming the scientific landscape often stem from philosophical thought, just as symbolic logic and computer science were born from the early analytic philosophy, and for the very reason they impact our global worldview as a coherent whole as well as local knowledge production in different specialised domains. Here we take first steps in elucidating rich philosophical contexts in which Samson Abramsky’s far-reaching work centring around categorical science (...) as a new kind of science may be placed, explicated, and articulated. We argue, inter alia, that Abramsky’s work, as a whole, may be construed as demonstrating the categorical unity of science, or rather the sciences, in a mathematically rigorous, down-to-earth manner, which has been a salient feature of his work. At the same time we trace his intellectual history, leading from duality, to intensionality, and to contextuality, and place it in a broader context of philosophy beyond the analytic-continental divide, namely towards the reintegration of them as in the post-analytic tradition. Besides, we address issues in philosophy of category theory, such as the foundational autonomy of category theory and the (presumably two) dogmas of set-theoretical foundationalism, which Abramsky actually touch upon in one of his few philosophically inclined works. As to philosophy of category theory, we also address categorical structuralism as higher-order structuralism, categorical epistemology as elucidating higher-order meta-laws, and categorical ontology as allowing for reduction of ontological commitment via structural realism, the structuralist resolution of Benaceraff’s dilemma, and the pluralistic multiverse view of science as opposed to the set-theoretical reductionist ‘universe’ view. We conclude by speculating about the existence of the Oxford School of (Pluralistic) Unified Science as opposed to the Vienna Circle of (Monistic) Unified Science and to the Stanford School of (Pluralistic) Disunified Science; Categorical Unified Science may potentially allow us to reconcile the two camps on the unity and disunity of science whilst doing justice to both of them. Categorical unity arguably allows for unification via epistemological and ontological networking, and via knowledge transfer thus enabled, rather than unification via the reduction of everything and every truth to a single foundationalist framework, whilst taking at face value disunity, plurality, and diversity, and their significance in science and in human civilisation as a whole. (shrink)

The purpose of this paper is an axiomatic study of the interrelations between certain continuity properties. We show that every mapping is sequentially continuous if and only if it is sequentially nondiscontinuous and strongly extensional, and that "every mapping is strongly extensional", "every sequentially nondiscontinuous mapping is sequentially continuous", and a weak version of Markov's principle are equivalent. Also, assuming a consequence of Church's thesis, we prove a version of the Kreisel-Lacombe-Shoenfield-Tsĕitin theorem.

We systematically study several principles and give a principle which is weaker than disjunctive Markov’s principle. We also show that the principle is underivable and strictly weaker than MP∨ in certain extensions of the system EL of elementary analysis.

ZusammenfassungIm Mittelpunkt des Beitrags steht die Übertragung ausgewählter Kapitel aus den 1955 niedergelegten autobiographischen Erinnerungen des japanischen Bakteriologen Taichi Kitashima, in denen Kitashima stark persönlich gefärbt über seinen Aufenthalt in Marburg berichtet. Wie andere japanische Mediziner seiner Generation verbrachte Kitashima mehrere Jahre in Deutschland, um dort bei dem Serumforscher Emil von Behring zu arbeiten und sich weiterzubilden. Der Kontakt war über Kitashimas Lehrer Shibasaburô Kitasato zustande gekommen, mit dem Behring in Berlin über Fragen der Immunologie geforscht hatte. Im „Kommentar“ wird (...) diskutiert, inwieweit die von Kitashima in der zeitlichen Distanz von 50 Jahren getroffene Einschätzung des Deutschlandaufenthalts als „vergeudete Zeit“ als zutreffend anzusehen ist, welche Vorteile ihm aus den europäischen Kontakten, zu denen auch Begegnungen im Pariser Pasteur-Institut gehörten, erwuchsen und aus welchen Gründen sie im Nationalsozialismus wiederbelebt wurden. (shrink)

This paper explores relationships between many-valued logic and fuzzy topology from the viewpoint of duality theory. We first show a fuzzy topological duality for the algebras of Łukasiewicz n -valued logic with truth constants, which generalizes Stone duality for Boolean algebras to the n -valued case via fuzzy topology. Then, based on this duality, we show a fuzzy topological duality for the algebras of modal Łukasiewicz n -valued logic with truth constants, which generalizes Jónsson-Tarski duality for modal algebras to the (...) n -valued case via fuzzy topology. We emphasize that fuzzy topological spaces naturally arise as spectrums of algebras of many-valued logics. (shrink)

Many existence propositions in constructive analysis are implied by the lesser limited principle of omniscience LLPO; sometimes one can even show equivalence. It was discovered recently that some existence propositions are equivalent to Bouwer's fan theorem FAN if one additionally assumes that there exists at most one object with the desired property. We are providing a list of conditions being equivalent to FAN, such as a unique version of weak König's lemma. This illuminates the relation between FAN and LLPO. Furthermore, (...) we give a short and elementary proof of the fact that FAN is equivalent to each positive valued function with compact domain having positive infimum. (shrink)

We study the distributivity of the bounded ideal on Pkλ and answer negatively to a question of Johnson in [13]. The size of non-normal ideals with the partition property is also studied.