{"title":"WKL$\\mathsf{WKL}下实值连续函数的编码$","authors":"Tatsuji Kawai","doi":"10.1002/malq.202200031","DOIUrl":null,"url":null,"abstract":"<p>In the context of constructive reverse mathematics, we show that weak Kőnig's lemma (<math>\n <semantics>\n <mi>WKL</mi>\n <annotation>$\\mathsf {WKL}$</annotation>\n </semantics></math>) implies that every pointwise continuous function <math>\n <semantics>\n <mrow>\n <mi>f</mi>\n <mo>:</mo>\n <mo>[</mo>\n <mn>0</mn>\n <mo>,</mo>\n <mn>1</mn>\n <mo>]</mo>\n <mo>→</mo>\n <mi>R</mi>\n </mrow>\n <annotation>$f : [0,1]\\rightarrow \\mathbb {R}$</annotation>\n </semantics></math> is induced by a code in the sense of reverse mathematics. This, combined with the fact that <math>\n <semantics>\n <mi>WKL</mi>\n <annotation>$\\mathsf {WKL}$</annotation>\n </semantics></math> implies the Fan theorem, shows that <math>\n <semantics>\n <mi>WKL</mi>\n <annotation>$\\mathsf {WKL}$</annotation>\n </semantics></math> implies the uniform continuity theorem: every pointwise continuous function <math>\n <semantics>\n <mrow>\n <mi>f</mi>\n <mo>:</mo>\n <mo>[</mo>\n <mn>0</mn>\n <mo>,</mo>\n <mn>1</mn>\n <mo>]</mo>\n <mo>→</mo>\n <mi>R</mi>\n </mrow>\n <annotation>$f : [0,1]\\rightarrow \\mathbb {R}$</annotation>\n </semantics></math> has a modulus of uniform continuity. Our results are obtained in Heyting arithmetic in all finite types with quantifier-free axiom of choice.</p>","PeriodicalId":49864,"journal":{"name":"Mathematical Logic Quarterly","volume":"69 3","pages":"370-391"},"PeriodicalIF":0.4000,"publicationDate":"2023-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Coding of real-valued continuous functions under \\n \\n WKL\\n $\\\\mathsf {WKL}$\",\"authors\":\"Tatsuji Kawai\",\"doi\":\"10.1002/malq.202200031\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>In the context of constructive reverse mathematics, we show that weak Kőnig's lemma (<math>\\n <semantics>\\n <mi>WKL</mi>\\n <annotation>$\\\\mathsf {WKL}$</annotation>\\n </semantics></math>) implies that every pointwise continuous function <math>\\n <semantics>\\n <mrow>\\n <mi>f</mi>\\n <mo>:</mo>\\n <mo>[</mo>\\n <mn>0</mn>\\n <mo>,</mo>\\n <mn>1</mn>\\n <mo>]</mo>\\n <mo>→</mo>\\n <mi>R</mi>\\n </mrow>\\n <annotation>$f : [0,1]\\\\rightarrow \\\\mathbb {R}$</annotation>\\n </semantics></math> is induced by a code in the sense of reverse mathematics. This, combined with the fact that <math>\\n <semantics>\\n <mi>WKL</mi>\\n <annotation>$\\\\mathsf {WKL}$</annotation>\\n </semantics></math> implies the Fan theorem, shows that <math>\\n <semantics>\\n <mi>WKL</mi>\\n <annotation>$\\\\mathsf {WKL}$</annotation>\\n </semantics></math> implies the uniform continuity theorem: every pointwise continuous function <math>\\n <semantics>\\n <mrow>\\n <mi>f</mi>\\n <mo>:</mo>\\n <mo>[</mo>\\n <mn>0</mn>\\n <mo>,</mo>\\n <mn>1</mn>\\n <mo>]</mo>\\n <mo>→</mo>\\n <mi>R</mi>\\n </mrow>\\n <annotation>$f : [0,1]\\\\rightarrow \\\\mathbb {R}$</annotation>\\n </semantics></math> has a modulus of uniform continuity. Our results are obtained in Heyting arithmetic in all finite types with quantifier-free axiom of choice.</p>\",\"PeriodicalId\":49864,\"journal\":{\"name\":\"Mathematical Logic Quarterly\",\"volume\":\"69 3\",\"pages\":\"370-391\"},\"PeriodicalIF\":0.4000,\"publicationDate\":\"2023-07-24\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Mathematical Logic Quarterly\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/malq.202200031\",\"RegionNum\":4,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"LOGIC\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Mathematical Logic Quarterly","FirstCategoryId":"100","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/malq.202200031","RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"LOGIC","Score":null,"Total":0}
Coding of real-valued continuous functions under
WKL
$\mathsf {WKL}$
In the context of constructive reverse mathematics, we show that weak Kőnig's lemma () implies that every pointwise continuous function is induced by a code in the sense of reverse mathematics. This, combined with the fact that implies the Fan theorem, shows that implies the uniform continuity theorem: every pointwise continuous function has a modulus of uniform continuity. Our results are obtained in Heyting arithmetic in all finite types with quantifier-free axiom of choice.
期刊介绍:
Mathematical Logic Quarterly publishes original contributions on mathematical logic and foundations of mathematics and related areas, such as general logic, model theory, recursion theory, set theory, proof theory and constructive mathematics, algebraic logic, nonstandard models, and logical aspects of theoretical computer science.