{"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":0,"journal":{"name":"","volume":null,"pages":null},"PeriodicalIF":0.0,"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\":0,\"journal\":{\"name\":\"\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.0,\"publicationDate\":\"2023-07-24\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/malq.202200031\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"","FirstCategoryId":"100","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/malq.202200031","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","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.