Ramsey's Theorem and the Pigeonhole Principle in Intuitionistic Mathematics

Type: Article
Publication Date: 1993-04-01
Citations: 38
DOI: https://doi.org/10.1112/jlms/s2-47.2.193

Abstract

At first sight, the argument which F. P. Ramsey gave for (the infinite case of) his famous theorem from 1927, is hopelessly unconstructive. If suitably reformulated, the theorem is true intuitionistically as well as classically: we offer a proof which should convince both the classical and the intuitionistic reader.

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  • Journal of the London Mathematical Society
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At first sight, the argument which F.P. Ramsey gave for (the infinite case of) his famous theorem from 1927, is hopelessly unconstructive. If suitably reformulated, the theorem is true intuitionistically … At first sight, the argument which F.P. Ramsey gave for (the infinite case of) his famous theorem from 1927, is hopelessly unconstructive. If suitably reformulated, the theorem is true intuitionistically as well as classically: we offer a proof which should convince both the classical and the intuitionistic reader.
In his essay entitled ‘Mathematical Logic’ written in 1926, Ramsey gives his opinion of the evolution of mathematical logic after the publication of Principia Mathematica. The essay is largely a … In his essay entitled ‘Mathematical Logic’ written in 1926, Ramsey gives his opinion of the evolution of mathematical logic after the publication of Principia Mathematica. The essay is largely a defence of the ideas of logicism against the attacks by Hilbert's formalism and Brouwer's intuitionism. Ramsey had already criticized Hilbert and Brouwer in ‘The Foundation of Mathematics’, and ‘Mathematical Logic’ is only a popular version of this criticism.
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Ramsey theory

2019-06-12

Ramsey Theory

2010-08-12

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We study different formalizations of finite sets in homotopy type theory to obtain a general definition that exhibits both the computational facilities and the proof principles expected from finite sets. … We study different formalizations of finite sets in homotopy type theory to obtain a general definition that exhibits both the computational facilities and the proof principles expected from finite sets. We use higher inductive types to define the type K(A) of "finite sets over type A" à la Kuratowski without assuming that K(A) has decidable equality. We show how to define basic functions and prove basic properties after which we give two applications of our definition.
L.E.J. Brouwer made a mistake in the formulation of his famous bar theorem, as was pointed out by S.C. Kleene. By repeating this mistake several times, Brouwer has caused confusion. … L.E.J. Brouwer made a mistake in the formulation of his famous bar theorem, as was pointed out by S.C. Kleene. By repeating this mistake several times, Brouwer has caused confusion. We consider the assumption underlying his bar theorem, calling it Brouwer's Thesis. This assumption is not refuted by Kleene's example and we use it to obtain a conclusion different from Brouwer's. Thus we come to support a view first expressed and defended by E. Martino and P. Giaretta in [Martino 1981]. We also indicate that Brouwer's Thesis has many more applications than Brouwer dreamt of.
We use Gödel's dialectica interpretation to produce a computational version of the well-known proof of Ramsey's theorem by Erdős and Rado. Our proof makes use of the product of selection … We use Gödel's dialectica interpretation to produce a computational version of the well-known proof of Ramsey's theorem by Erdős and Rado. Our proof makes use of the product of selection functions, which forms an intuitive alternative to Spector's bar recursion when interpreting proofs in analysis. This case study is another instance of the application of proof theoretic techniques in mathematics.
Abstract We investigate which part of Brouwer’s Intuitionistic Mathematics is finitistically justifiable or guaranteed in Hilbert’s Finitism, in the same way as similar investigations on Classical Mathematics (i.e., which part … Abstract We investigate which part of Brouwer’s Intuitionistic Mathematics is finitistically justifiable or guaranteed in Hilbert’s Finitism, in the same way as similar investigations on Classical Mathematics (i.e., which part is equiconsistent with $\textbf {PRA}$ or consistent provably in $\textbf {PRA}$ ) already done quite extensively in proof theory and reverse mathematics. While we already knew a contrast from the classical situation concerning the continuity principle, more contrasts turn out: we show that several principles are finitistically justifiable or guaranteed which are classically not. Among them are: (i) fan theorem for decidable fans but arbitrary bars; (ii) continuity principle and the axiom of choice both for arbitrary formulae; and (iii) $\Sigma _2$ induction and dependent choice. We also show that Markov’s principle MP does not change this situation; that neither does lesser limited principle of omniscience LLPO (except the choice along functions); but that limited principle of omniscience LPO makes the situation completely classical.
We study different formalizations of finite sets in homotopy type theory to obtain a general definition that exhibits both the computational facilities and the proof principles expected from finite sets. … We study different formalizations of finite sets in homotopy type theory to obtain a general definition that exhibits both the computational facilities and the proof principles expected from finite sets. We use higher inductive types to define the type K(A) of "finite sets over type A" à la Kuratowski without assuming that K(A) has decidable equality. We show how to define basic functions and prove basic properties after which we give two applications of our definition.
In this paper we look at streamless sets, recently investigated by Coquand and Spiwack. A set is streamless if every stream over that set contain a duplicate. It is an … In this paper we look at streamless sets, recently investigated by Coquand and Spiwack. A set is streamless if every stream over that set contain a duplicate. It is an open question in constructive mathematics whether the Cartesian product of two streamless sets is streamless. We look at some settings in which the Cartesian product of two streamless sets is indeed streamless; in particular, we show that this holds in Martin-Loef intentional type theory when at least one of the sets have decidable equality. We go on to show that the addition of functional extensionality give streamless sets decidable equality, and then investigate these results in a few other constructive systems.
The paper is a contribution to intuitionistic reverse mathematics. We work in a weak formal system for intuitionistic analysis. The Principle of Open Induction on Cantor space is the statement … The paper is a contribution to intuitionistic reverse mathematics. We work in a weak formal system for intuitionistic analysis. The Principle of Open Induction on Cantor space is the statement that every open subset of Cantor space that is progressive with respect to the lexicographical ordering of Cantor space coincides with Cantor space. The Approximate-Fan Theorem is an extension of the Fan Theorem that follows from Brouwer's principle of induction on bars in Baire space and implies the Principle of Open Induction on Cantor space. The Principle of Open Induction in Cantor space implies the Fan Theorem, but, conversely the Fan Theorem does not prove the Principle of Open Induction on Cantor space. We list a number of equivalents of the Principle of Open Induction on Cantor space and also a number of equivalents of the Approximate-Fan Theorem.
The paper is an introduction to intuitionistic mathematics. The paper is an introduction to intuitionistic mathematics.
We present a locale that abstracts over the necessary ingredients for constructing a minimal bad sequence, as required in classical proofs of Higman's lemma and Kruskal's tree theorem. We present a locale that abstracts over the necessary ingredients for constructing a minimal bad sequence, as required in classical proofs of Higman's lemma and Kruskal's tree theorem.
In constructive mathematics, several nonequivalent notions of finiteness exist. In this paper, we continue the study of Noetherian sets in the dependently typed setting of the Agda programming language. We … In constructive mathematics, several nonequivalent notions of finiteness exist. In this paper, we continue the study of Noetherian sets in the dependently typed setting of the Agda programming language. We want to say that a set is Noetherian, if, when we are shown elements from it one after another, we will sooner or later have seen some element twice. This idea can be made precise in a number of ways. We explore the properties and connections of some of the possible encodings. In particular, we show that certain implementations imply decidable equality while others do not, and we construct counterexamples in the latter case. Additionally, we explore the relation between Noetherianness and other notions of finiteness.
Mixing induction and coinduction, we study alternative definitions of streams being finitely red. We organize our definitions into a hierarchy including also some well-known alternatives in intuitionistic analysis. The hierarchy … Mixing induction and coinduction, we study alternative definitions of streams being finitely red. We organize our definitions into a hierarchy including also some well-known alternatives in intuitionistic analysis. The hierarchy collapses classically, but is intuitionistically of strictly decreasing strength. We characterize the differences in strength in a precise way by weak instances of the Law of Excluded Middle.
We study S1S and Büchi automata in the constructive type theory of the Coq proof assistant. For UP semantics (ultimately periodic sequences), we verify Büchi's translation of formulas to automata … We study S1S and Büchi automata in the constructive type theory of the Coq proof assistant. For UP semantics (ultimately periodic sequences), we verify Büchi's translation of formulas to automata and thereby establish decidability of S1S constructively. For AS semantics (all sequences), we verify Büchi's translation assuming that sequences over finite semigroups have Ramseyan factorisations (RF). Assuming RF, UP semantics and AS semantics agree. RF is a consequence of Ramsey's theorem and implies the infinite pigeonhole principle, which is known to be unprovable constructively. We show that each of the following properties holds for UP semantics but is equivalent to RF for AS semantics: excluded middle of formula satisfaction, excluded middle of automaton acceptance, and existence of complement automata.

References (2)

Let N be the set of natural numbers. If A ⊆ N , let [ A ] n denote the class of all n -element subsets of A . If … Let N be the set of natural numbers. If A ⊆ N , let [ A ] n denote the class of all n -element subsets of A . If P is a partition of [ N ] n into finitely many classes C 1 , …, C p , let H ( P ) denote the class of those infinite sets A ⊆ N such that [ A ] n ⊆ C i for some i . Ramsey's theorem [8, Theorem A] asserts that H ( P ) is nonempty for any such partition P . Our purpose here is to study what can be said about H ( P ) when P is recursive, i.e. each C i , is recursive under a suitable coding of [ N ] n . We show that if P is such a recursive partition of [ N ] n , then H ( P ) contains a set which is Π n 0 in the arithmetical hierarchy. In the other direction we prove that for each n ≥ 2 there is a recursive partition P of [ N ] n into two classes such that H ( P ) contains no Σ n 0 set. These results answer a question raised by Specker [12]. A basic partition is a partition of [ N ] 2 into two classes. In §§2, 3, and 4 we concentrate on basic partitions and in so doing prepare the way for the general results mentioned above. These are proved in §5. Our “positive” results are obtained by effectivizing proofs of Ramsey's theorem which differ from the original proof in [8]. We present these proofs (of which one is a generalization of the other) in §§4 and 5 in order to clarify the motivation of the effective versions.