How connected is the intuitionistic continuum?

1997 ◽  
Vol 62 (4) ◽  
pp. 1147-1150 ◽  
Author(s):  
Dirk Van Dalen

In the twenties Brouwer established the well-known continuity theorem “every real function is locally uniformly continuous,” [3, 2, 5]. From this theorem one immediately concludes that the continuum is indecomposable (unzerlegbar), i.e., if ℝ = A ∪ B and A ∩ B = ∅ (denoted by ℝ = A + B), then ℝ = A or ℝ = B.Brouwer deduced the indecomposability directly from the fan theorem (cf. the 1927 Berline Lectures, [7, p. 49]).The theorem was published for the first time in [6], it was used to refute the principle of the excluded middle: ¬∀x ∈ ℝ (x ∈ ℚ ∨ ¬x ∈ ℚ).The indecomposability of ℝ is a peculiar feature of constructive universa, it shows that ℝ is much more closely knit in constructive mathematics, than in classically mathematics. The classically comparable fact is the topological connectedness of ℝ. In a way this characterizes the position of ℝ: the only (classically) connected subsets of ℝ are the various kinds of segments. In intuitionistic mathematics the situation is different; the continuum has, as it were, a syrupy nature, one cannot simply take away one point. In the classical continuum one can, thanks to the principle of the excluded third, do so. To put it picturesquely, the classical continuum is the frozen intuitionistic continuum. If one removes one point from the intuitionistic continuum, there still are all those points for which it is unknown whether or not they belong to the remaining part.

2017 ◽  
Vol 28 (6) ◽  
pp. 942-990 ◽  
Author(s):  
VINCENT RAHLI ◽  
MARK BICKFORD

This paper extends the Nuprl proof assistant (a system representative of the class of extensional type theories with dependent types) withnamed exceptionsandhandlers, as well as a nominalfreshoperator. Using these new features, we prove a version of Brouwer's continuity principle for numbers. We also provide a simpler proof of a weaker version of this principle that only uses diverging terms. We prove these two principles in Nuprl's metatheory using our formalization of Nuprl in Coq and reflect these metatheoretical results in the Nuprl theory as derivation rules. We also show that these additions preserve Nuprl's key metatheoretical properties, in particular consistency and the congruence of Howe's computational equivalence relation. Using continuity and the fan theorem, we prove important results of Intuitionistic Mathematics: Brouwer's continuity theorem, bar induction on monotone bars and the negation of the law of excluded middle.


2018 ◽  
Vol 83 (04) ◽  
pp. 1363-1375 ◽  
Author(s):  
JOSEF BERGER ◽  
GREGOR SVINDLAND

AbstractIn the framework of Bishop’s constructive mathematics we introduce co-convexity as a property of subsets B of ${\left\{ {0,1} \right\}^{\rm{*}}}$, the set of finite binary sequences, and prove that co-convex bars are uniform. Moreover, we establish a canonical correspondence between detachable subsets B of ${\left\{ {0,1} \right\}^{\rm{*}}}$ and uniformly continuous functions f defined on the unit interval such that B is a bar if and only if the corresponding function f is positive-valued, B is a uniform bar if and only if f has positive infimum, and B is co-convex if and only if f satisfies a weak convexity condition.


Author(s):  
Andrew McNeillie
Keyword(s):  

It is now widely acknowledged, and far beyond Ireland, that Tim Robinson’s two volumes jointly known as Stones of Aran (‘Pilgrimage’ and ‘Labyrinth’) are modern classics, exemplary in every way of how to write about place and to do so with a formal, literary accomplishment that more than earns the right to nod at Ruskin’s own classic. In 2012, Robinson went back to Árainn, the largest of the three islands, for the first time in nearly ten years. He did so at the urging of Andrew McNeillie, with whom he spent two and a half days revisiting old haunts. This chapter makes account of the occasion and uses, in the process, a unique document provided by Robinson as an experiment in annotating his work. This prompts McNeillie to investigate some of his own annotations and footnotes to Aran.


Author(s):  
Talbot C. Imlay

This chapter examines the post-war efforts of European socialists to reconstitute the Socialist International. Initial efforts to cooperate culminated in an international socialist conference in Berne in February 1919 at which socialists from the two wartime camps met for the first time. In the end, however, it would take four years to reconstitute the International with the creation of the Labour and Socialist International (LSI) in 1923. That it took so long to do so is a testimony to the impact of the Great War and to the Bolshevik revolution. Together, these two seismic events compelled socialists to reconsider the meaning and purpose of socialism. The search for answers sparked prolonged debates between and within the major parties, profoundly reconfiguring the pre-war world of European socialism. One prominent stake in this lengthy process, moreover, was the nature of socialist internationalism—both its content and its functioning.


2021 ◽  
Vol 10 (11) ◽  
pp. 2340
Author(s):  
Lucia Borriello ◽  
John Condeelis ◽  
David Entenberg ◽  
Maja H. Oktay

Although metastatic disease is the primary cause of mortality in cancer patients, the mechanisms leading to overwhelming metastatic burden are still incompletely understood. Metastases are the endpoint of a series of multi-step events involving cancer cell intravasation, dissemination to distant organs, and outgrowth to metastatic colonies. Here we show, for the first-time, that breast cancer cells do not solely disseminate to distant organs from primary tumors and metastatic nodules in the lymph nodes, but also do so from lung metastases. Thus, our findings indicate that metastatic dissemination could continue even after the removal of the primary tumor. Provided that the re-disseminated cancer cells initiate growth upon arrival to distant sites, cancer cell re-dissemination from metastatic foci could be one of the crucial mechanisms leading to overt metastases and patient demise. Therefore, the development of new therapeutic strategies to block cancer cell re-dissemination would be crucial to improving survival of patients with metastatic disease.


1954 ◽  
Vol 19 (2) ◽  
pp. 189-218 ◽  
Author(s):  
G. Caton-Thompson

The material here described was found in the Hadhramaut by Elinor Gardner and myself between November 1937 and March 1938. My personal investigation of the Palaeolithic Age was limited by pre-Islamic excavations, and I am therefore indebted to her for the gathering of most of the specimens in situ in terrace gravels, and to her detailed study of their positions.The collection consists mainly of groups from four fairly widely separated localities; the physiography of these has already been outlined in a comprehensive paper published in the Geographical Journal. Whenever appropriate to the purpose of this account, which is to place for the first time on illustrated record all we observed about the palaeoliths, I have reused in this different context illustrations of Quaternary environment which appeared in that Journal. With thanks I acknowledge the permission of the Royal Geographical Society to do so.


Author(s):  
Moh Rifai

<p>Parents are obliged to take care of their children’s future, especially by rendering sufficient education. Children are believed to bring about happiness every now and then, who generate family’s pride up to the almighty judication. Some people are save and some are not in that court, where children will give sigificant contribution in it. That’s why the children’s well being has become the parents obligation. To bring about children’s well being, parents should also render the good treatments during the life cycle of their children. The main duties of parents for their children are giving them the good names, sending them to the good schools where they can learn religion, and marry them to their good spouses. Psychologically, when children are sent to school for the first time, they will feel that they are put apart from parents’ care, so that may of them have to go difficult phase of adjustment. The adjustment includes that of education so as to run as naturally as possible. To get the naturality of the education delegation, teachers and educators are obliged to be able to nurture any value to students as naturally as possible. Parenting model of teaching serves the requirements of teaching children just the way the parrents do, so that it is assumptively effective in teaching elementary students by taking consideration on the psychologial aspect of children.</p><p> </p><p>Key words:   Parenting Model of teaching, children education optimalization</p>


2015 ◽  
Vol 62 (1) ◽  
pp. 1-12
Author(s):  
José A. Guerrero ◽  
Nelson Merentes ◽  
José L. Sánchez

Abstract In this paper we present the concept of total κ-variation in the sense of Hardy-Vitali-Korenblum for a real function defined in the rectangle Iab⊂R2. We show that the space κBV(Iab, R) of real functions of two variables with finite total κ-variation is a Banach space endowed with the norm ||f||κ = |f (a)| + κTV( f, Iab). Also, we characterize the Nemytskij composition operator H that maps the space of functions of two real variables of bounded κ-variation κBV(Iab, R) into another space of a similar type and is uniformly bounded (or Lipschitzian or uniformly continuous).


2014 ◽  
Vol 79 (3) ◽  
pp. 792-813 ◽  
Author(s):  
ROBERT S. LUBARSKY ◽  
HANNES DIENER

AbstractVarieties of the Fan Theorem have recently been developed in reverse constructive mathematics, corresponding to different continuity principles. They form a natural implicational hierarchy. Some of the implications have been shown to be strict, others strict in a weak context, and yet others not at all, using disparate techniques. Here we present a family of related Kripke models which separates all of the as yet identified fan theorems.


2014 ◽  
Vol 79 (4) ◽  
pp. 1092-1119 ◽  
Author(s):  
WILL BONEY

AbstractWe show that Shelah’s Eventual Categoricity Conjecture for successors follows from the existence of class many strongly compact cardinals. This is the first time the consistency of this conjecture has been proven. We do so by showing that every AEC withLS(K) below a strongly compact cardinalκis <κ-tame and applying the categoricity transfer of Grossberg and VanDieren [11]. These techniques also apply to measurable and weakly compact cardinals and we prove similar tameness results under those hypotheses. We isolate a dual property to tameness, calledtype shortness, and show that it follows similarly from large cardinals.


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