<?xml version="1.0" encoding="utf-8"?><feed xmlns="http://www.w3.org/2005/Atom" ><generator uri="https://jekyllrb.com/" version="3.10.0">Jekyll</generator><link href="https://willkwon-math.kr/feed.xml" rel="self" type="application/atom+xml" /><link href="https://willkwon-math.kr/" rel="alternate" type="text/html" /><updated>2026-09-13T22:08:05+00:00</updated><id>https://willkwon-math.kr/feed.xml</id><title type="html">Hyunwoo Kwon (Will)</title><subtitle>Ph.D. student and Researcher in Analysis&amp;PDEs.</subtitle><entry><title type="html">My explanation to the recent statement ‘A Severe Misalignment of AI in Mathematics’</title><link href="https://willkwon-math.kr/2026/09/13/SMCK.html" rel="alternate" type="text/html" title="My explanation to the recent statement ‘A Severe Misalignment of AI in Mathematics’" /><published>2026-09-13T10:00:40+00:00</published><updated>2026-09-13T10:00:40+00:00</updated><id>https://willkwon-math.kr/2026/09/13/SMCK</id><content type="html" xml:base="https://willkwon-math.kr/2026/09/13/SMCK.html"><![CDATA[<p>I got a request to share an expert opinion through the Science Media Center Korea on ‘A Severe Misalignment of AI in Mathematics’ given at <a href="https://mathandai.org">https://mathandai.org/</a>.</p>

<p>Other than me, <a href="https://www.smck.or.kr/viewer/6aa6283f57af92394f2d040f">two people have submitted their expert opinions</a> Prof. Sang-il Oum and Prof. Han Woo Park on 9/13/2026. Most likely, I thought that it was important to share some points of view that cannot be put into one particular side. It is really easy to look at the situation in one framework, but I already shared my opinion on LLM in several articles in this blog (see <a href="https://willkwon-math.kr/2026/08/28/declare">the most recent one</a>) as well as my personal blog in Korean. You cannot call me a Luddite, and I decided not to use this technology in math research for a while because of tech-driven influence and issues on the scientific publications which was pointed out in the blog post.</p>

<p>While I got a translation of this article into English via Claude, I did not like the word choice in English at all, and I don’t like the translation it suggested. So I won’t share that version at all.
I am not sure whether I could rewrite this in English.</p>

<p>I answered the following questions. I appreciate Shin-Young Yoon for posing this question to stimulate my thought.</p>
<ol>
  <li>What’s your opinion on this statement as mathematician or AI researcher?</li>
  <li>In this statement, it says “Our ideas we disseminate in talks, private discussions and careful writeups, connecting them to the previous ideas of others. These processes invariably take time and are based on human interaction”. What do you feel the change after the generative AI techology is on hand?</li>
  <li>Since Leiden declaration, there are several statement given by Mathematician. Do you think these statements have broad impact to our society?</li>
  <li>Do you agree a competition on solving conjecture as it was pointed out in the statement? Do you think it has a positive influence?</li>
  <li>If you think there is a problem, then what would be a possible way to resolve this issue?</li>
  <li>It seems that it is closely related to the ethical issue regarding the resolution of the finite-time blow-up for the Navier-Stokes equations claimed by OpenAI. Can you share any opinion regarding this?</li>
  <li>Besides, what potential issue that mathematicians have to think about it which was not mentioned in the statement?</li>
</ol>

<p><span style="color: blue;">Q1. 이번 성명의 내용에 대한 수학 및 인공지능 분야 전문가들께서는 어떻게 생각하시는지요.</span></p>

<p>가장 전면으로 나서고 있는 <a href="https://www.ahmath.org/">인간수학협회</a>의 성명문에 대해서는 동의하지 않는 사람들도 많지만, 근래 수학계에서 나왔던 성명문 중에서 제 주변만 하더라도 광범위하게 많은 사람들이 동의하고 있는 성명문이라고 생각합니다. 특히 지식의 평가, 인력 양성 방향에 대해서 조금씩 언급하고 있으나, 이 선언문에서는 200년간 현대 수학 연구가 어떻게 이루어지고 있는지를 잘 설명하면서 수학의 연구 방향과 문제를 바라보는 관점을 잘 설명하고 있다고 생각합니다. 그러나 수학과가 이 문제를 바라보고 있는 글임에도 불구하고, 다른 관점으로는 이 문제를 공감하지 못하는 분들도 있는 것 같아 적어도 제 관점에서 이 설명문의 이야기를 한글로 풀고자 합니다.</p>

<p>이미 성명문에서 잘 이야기하듯이, 수학 연구는 문제를 풀며 수학적 대상에 대한 고찰을 하는 방향으로 진행되어왔고, 그 핵심 주제에 대해서 더 명확한 이해를 하는 걸 목표로 해 왔습니다. 모든 사람들이 다 개개인의 취향과 생각이 다르듯이, 같은 대상이라고 할 지라도 사람이 가진 그 고유한 역사에 따라 문제를 바라보는 시선이 다르기에, 그런 부분이 수학의 다채로움을 만들어왔습니다. 제 전공인 편미분방정식을 예로 든다면, 같은 방정식이라고 할 지라도, 어떤 사람은 어떠한 정칙성을 보장할 수 있는 최소한의 가정이 무엇인지에 관심을 갖는 사람이 있고, 이 방정식에서 나오는 동역학이 어떤식으로 일어나는지에 대한 관심을 갖는 사람이 있으며, 어떤 사람은 어떤 물리적 실체를 잡기 위해 자칫 괴상해보일 수 있는 함수공간을 설정해서 그 물리적 실체를 잡아내는 연구를 하는 사람도 있습니다.</p>

<p>반면에 수학을 도구로 사용해서 그간 연구를 했던 분야의 종사자가 쓴 글들을 보면, 수학 연구가 행해지고 있는 관행과 그 목적을 이해하려는 노력을 하지 않는 글들이 대부분이었습니다. 수학에서 그간 연구하던 난제가 풀리는 과정은 저는 화룡점정에 비유하고 싶습니다. 용의 몸통을 모두 다 그리는 과정을 수학의 한 분야에 대한 얼개를 이해하고, 비늘을 하나씩 채우며 그 문제에 대한 이해를 하나씩 채워나갑니다. 그리고 그 모든 것이 다 끝나서 눈을 그리는 과정, 이게 난제가 그간 풀리는 과정이었습니다. 난제가 풀리기 위해서는 그만한 수학적 이해가 충분한 상태로 한 두 스텝만 넘기면 문제를 풀 수 있는 과정들이 있는 상태들을 대부분 보아 왔습니다. 난제라는 것을 설정함으로써 그 문제가 담고 있는 여러 관점을 더 개발하고, 수학자들은 이 수학적 대상에 대한 명확한 이해를 해왔습니다. 그리고 수학 문제에 대해서 참과 거짓보다 더 중요한 것은, 이 참과 거짓으로 이끌어가는 그 논리와 도구를 만들어 가는 것에 관심이 있다고 생각합니다. 사람들이 100년 이상 못 푼 난제를 풀어낸 것이 잘 된 것이 아니냐라는 생각을 하고 있는데, 이는 수학 연구를 직접 하지 않고 외부자 입장에서 쉽게 말하는 문제라고 생각해 매우 유감입니다.</p>

<p>마지막으로 이 성명문에서는 급하게 발표되어 새로운 방법과 아이디어의 발굴, 그리고 관련 선행 연구에 대한 인용을 위한 충분한 시간이 부족하여 저작자 표시 및 표절 문제가 발생하는 것에 대해서 심히 우려를 표하고 있습니다. 특히 이번에 OpenAI가 문제를 풀었다고 주장한 Navier-Stokes 방정식의 대역 정칙성 문제에 대해서는 반드시 언급되어야 하는 참고문헌이 누락된 것을 확인했습니다. 초기에 Gonzalo Cao-Labora(EPFL)이 <a href="https://x.com/GonZalocla/status/2097386569082577175">X에서 캡쳐한 스크린샷</a> 에서도 언급되었듯이 기존의 수많은 시도에 대한 언급은 없었던 것은 물론이며 인용된 연구도 AI가 적당히 끼워맞추기로 인용한 수준이었습니다. 제가 9월 11일 금요일에 하버드에서 Javier Gomez-Serrano (브라운대학교) 교수의 해설 강연을 통해 이 나비에-스톡스 방정식의 폭발해를 건설한 과정을 이해한 바에 따르면, 지금 버전에서도 수학연구의 관점에서 이 연구를 진행했을 때 참고해서 진행했을 법한 논문이 전혀 언급되지 않았습니다.</p>

<p>타 전공자와의 토론을 통해, 적어도 수학 내부에서는 서스턴의 글을 시작으로 어느 정도 기초적인 합의가 되었던, 수학을 하는 활동에 대한 정의가 다른 분야의 종사자에게는 다르게 보일 수 있겠다는 생각이 들었습니다. 결국 지식의 생산 기준을 무엇으로 보느냐에 따라 이 문제를 다른 관점으로 볼 수 있겠구나라는 것을 인지했고, 인접 분야의 전공자들이 이 성명문에 대해 다른 관점으로 볼 수 있다는 생각을 해보았습니다. 외연 확장을 위해 어떤 방향으로 이 이야기를 할 수 있을지에 대한 고민이 더 필요하다고 생각했습니다.</p>

<p><a href="https://proofsandprompts.com/">Proofs and Prompts</a>에서도 볼 수 있듯이 이 LLM 기반의 영향력에 대해서 다양한 방향으로 걱정하는 사람들이 많습니다. 수학자들이 어떤 식으로 이 문제들을 바라보는지 다양한 관점을 보고자 한다면, 이 포럼에 나와있는 토론을 보셨으면 좋겠습니다.</p>

<p><span style="color: blue;">Q2. 이번 선언에서 “아이디어는 강연, 개별 토론, 그리고 신중한 논문 작성을 통해 공유되며, 다른 사람들의 기존 아이디어와 연결된다. 이런 과정은 필연적으로 시간이 걸리고 인간적인 상호작용을 기반으로 한다”고 밝혔습니다. 이런 전통적인 교육과 인적 교류에 기반한 수학 발전 양상이 인공지능 등장으로 실제로 현장에서 바뀌고 있다고 느끼시는지요.</span></p>

<p>심각하게 바뀌고 있습니다. 지금 ChatGPT 5.1 이후 arXiv에 각종 논문들이 생산되는 속도가 지나치게 빨라지고 있어 어떤 논문이 있는지 추적조차 힘든 상황이 발생할 정도입니다. 저는 아침에 컴퓨터를 켜면 첫 화면이 Analysis&amp;PDE arXiv 페이지인데 기존보다 연구 결과가 더 많아지고 있는 걸 느끼고 있습니다. 그런데 올해부터는 특히 AI disclosure statement가 서서히 나오는데, 많은 부분에서 그냥 무의미한 수준으로 AI LLM과 대화를 통해 이런 반례를 찾았고, 사람이 검증했다는 식의 설명입니다. 수학에서 반례의 건설은 매우 중요합니다. 그 이야기는 이 방향으로는 또는 이런 가정에서는 우리가 원하는 답을 얻을 수 있다는 것을 알려주는 신호이기 때문입니다.</p>

<p>역사적인 사례를 하나 들겠습니다. 디레클레는 아주 혁신적인 방법으로 에너지 범함수의 최소화 하는 함수는 편미분방정식의 해가 되는 획기적인 방법론을 제시했습니다. 이 방법론은 현대에서는 변분론(calculus of variations)이라 불리며 지금도 많은 사람들이 연구하고 있는 분야입니다. 이 획기적인 방법을 리만이 자신의 리만곡면 연구에 적극적으로 사용했으나, 후에 바이어슈트라스가 1870년대에 아다마르가 1906년에 디레클레 원리가 항상 성립하지 않다는 것을 반례로 보였습니다. 이 과정에서 힐버트는 이 방법론이 버려지면 안된다는 생각을 해 1900년에 이 문제를 바라볼 올바른 관점을 도입하여 이 반례를 제외할 수 있는 힐베르트 공간론을 만들어 이 문제를 해결해냈습니다.</p>

<p>그러나 지금의 연구에서는 LLM이 연구 수단으로 도입된 이후, 과도하게 반례 중심의 연구가 진행되고 있으며, LLM에 종속된 연구가 시작되고 있는 모습이 보이고 있습니다. 이렇게 되면, LLM이 잘 다루지 못하는 연구 주제에 대한 노력이 줄어들 가능성이 높습니다. 특히 현대 과학은 연구 성과에 대한 압박으로 인해 앞서 말한 힐베르트의 사례와 같은 것이 잘 일어날 수 있는 풍토가 생길지 걱정입니다.</p>

<p>그리고 이번에 Alpoge와 Buckmaster가 LLM을 이용해 나비에-스토크스 문제를 공략한다는 소문을 듣자마자 OpenAI가 자신의 프론티어 모델을 90시간 이상 소비하여 문제를 풀어냈다는 것은 여러 악신호를 주는 상황입니다. 큰 문제든 작은 문제든, 어떤 문제를 풀기 위해서는 많은 시간이 걸려왔으며 이 과정에서 수학자들은 발표장에서 내부적으로 세미나를 하거나, 다른 지역으로 가서 다른 구성원 앞에서 발표를 하며 문제의 방향에 대해서 토론을 하는 문화가 있었습니다. 그 대표적인 사례가 Cedric Villani와 Clement Mouhot가 해결한 Landau damping의 논문입니다. 이 논문에서는 서문에서 수 많은 수학자들에 대한 헌사를 첫 페이지에 담고 있습니다. 문제를 주도적으로 푸는 것은 두 사람이었지만, 이 두 사람들이 다른 사람과 대화하며 각자 시행착오들을 교류하며 어떻게 문제를 더 자연스럽게 바라볼지 교류한 끝에 문제를 해결했기 때문입니다.</p>

<p>저는 그래도 수학을 공부한지 이제 13년이 넘었기 때문에 과거에 세미나 끝나고 술 한잔 하면서 다양한 문제에 대한 관점을 교류하며, 이전에 생각하지도 못했던 주제를 귀동냥으로 들었는데, 그 이야기가 기억이 나 7년이 지나 제 새로운 프로젝트에 그 아이디어를 적용했고, 그 논문을 마무리하고 있습니다. 과연 이렇게 자신의 시행착오와 여러 가지 수학 노하우를 구술로 말하는 순간이 과거처럼 자유롭지는 않을 수 있겠다는 점이 매우 슬픕니다.</p>

<p>더불어, OpenAI가 학회장에 참석하며 연구에 대한 소문을 듣고 자신의 내부 머신으로 문제를 풀어서 그 문제를 오래 고민해 온 저자에게 다가가서 공저로 권위를 얻으려고 했다는 이야기도 들었습니다. 그 저자는 단칼에 거절했다고 들었습니다. 이런 사례도 나오는 상황에 누가 큰 문제를 공략하는 사람이 공개적으로 여러가지 부분적 진척을 공유하며 사람들이 더 좋은 방향으로 연구하는 그 흐름을 만들 수 있을까요?</p>

<p>교육 현장도 마찬가지입니다. 특히 학부생, 대학원 초창기에 연습 문제를 풀며 좌절을 하며 많은 어려움을 뚫고 새로운 아이디어로 문제를 해결하는 연습을 해야하는 상황에, 너무 강력한 유혹인 LLM이 곁에 있는 겁니다. LLM에 간단한 문제를 하나 대입하면 여러 가지 풀이가 있음에도 불구하고 하나의 답을 쉽게 얻을 수 있는 상황이니, 다양한 관점으로 학생들이 문제를 바라볼 수 있는 기회를 앗아가고 있습니다. 특히 수학 연구는 큰 문제를 풀기 전 많은 트레이닝이 필요한데, 이제 LLM으로 그런 입문 문제가 서서히 쉽게 풀리고 있어 주니어가 진입할 장벽이 더 높아졌다고 생각합니다.</p>

<p>마지막으로, 소셜네트워크의 탄생 당시에 사람들은 공론장이 될것이고 더 많은 사람이 연결될거라고 생각했었습니다. 그러나 10년이 지난 지금, 그런 역할을 하고 있나요? LLM에 대화하며 연구하는 것이 지금도 현실화되고 있는데, 사람과의 대화를 적극적으로 하는 시대가 멀어지고 기계와 대화하며 연구하며, LLM이 제시한 방향대로만 연구를 진행하는 미래가 되는 것에 대한 걱정이 있습니다.</p>

<p><span style="color: blue;">Q3. 라이덴 선언부터 벌써 여러 차례 이런 선언이 나오는데, 사회에 미치는 영향이 충분하다고 생각하시는지요.</span></p>

<p>이 부분은 아직 판단하기 이르다고 생각합니다. 원로 교수들은 성명서만 낼 것이 아니라, 정계와 산업계와 적극적으로 대화를 해야한다고 생각합니다. 특히 더 늦기 전에 한국도 정계와 많은 논의를 하여 자연과학이 위축되지 않는 방향을 잘 논의해야 한다고 생각합니다. 저를 비롯한 주니어들은 자신이 쓸모가 있음을 보이기 위해 애를 써야 할 시기입니다. 너그러운 마음을 가지고 후속세대를 위해 힘을 써주셨으면 좋겠습니다.</p>

<p><span style="color: blue;">Q4. 성명이 지적한 현재의 경쟁적 난제 풀이의 문제점에 동의하시는지요. 순기능도 충분히 크다고 느끼시는지요.</span></p>

<p>경쟁적 난제 풀이가 그간 수학사에서 많은 발전을 이끌어 왔다는 것은 부인할 수 없습니다. 그렇지만 저는 지금 산업계가 만들어낸 수학 연구흐름은 순기능보다 역기능이 많다고 생각합니다. 더 창의적인 생각, 다른 관점을 시도할 수 있는 긴 시간 동안 버틸 수 있는 문화에서 온다고 생각합니다. 그리고 독특한 관점을 수용할 수 있는 문화에서 온다고 생각합니다. LLM 기반 연구는 다양한 생각의 창발을 할 수 있는 여유를 주지 못하고, 진입단계에 있는 연구자들의 토양을 황폐화할 수 있다고 생각합니다.</p>

<p>저는 지금 논문을 하나 마무리하는 와중인데, 2주 전부터 수학 연구에서 AI를 한동안 쓰지 않기로 다짐하고 있었습니다. 물론 AI를 쓰면 빠른 속도로 쓸 수는 있겠지만, 사람이 읽었을 때 이 문제를 어떻게 바라보면 쉽게 계산할 수 있을지에 대한 고민을 더 하고 있던 와중이었고, 2주 지나 조금 더 간결하게 쉽게 이해할 수 있게 쓰는 방법을 찾을 수 있었습니다. 그러나 이런 식의 연구를 언제까지 진행할 수 있을지는 모르겠습니다. 이창호의 부득탐승에서 말한 것처럼 “뛰어들고 싶은 유혹이 강렬한 것을 외면하고 묵묵히 나의 길을 가는 것도 용기다.”라는 말을 되새기면서 앞으로 나아가려고 해도 흐름이 그렇지 못하다면 저도 따라가야하니까요.</p>

<p>이번 OpenAI가 나비에-스토크스 방정식 연구에 행한 것은 비판받아야 할 부분이 많습니다. 제가 편미분방정식 유체방정식 이론만 10년을 공부했는데, 올려놓은 논문의 세부적인 논법에 대한 설명이 이해가 안 될 정도이며, 이 연구를 시작할 수 있게 만든 아이디어를 만든 Cordoba와 Martinez-Zoroa는 표기법이 익숙치 않아 논문을 읽을 수가 없었다라고 논평을 했으며, 이번에 해설 강의를 한 Javier Gomez-Serrano도 논문의 아이디어를 이해라도 하기 위해 억지로 Claude에 대입해서 핵심만 추출할 정도로, 아직 한 명도 한 줄씩 읽을 엄두를 못내고 있습니다. 이건 수학자들의 역할이 아니라 지식을 생산한 곳의 책임이 더 필요합니다. 세상에 검증을 정말로 원하고, 수학의 발전에 진심으로 신경 쓸 모습이 있었다면, 이런 식으로 행해서는 절대로 안 된다고 생각합니다.</p>

<p>이는 밀레니엄 난제였던 푸앙카레 추측이 풀렸을 당시와는 전혀 다른 상황임을 강조하고 싶습니다. 페렐만은 짧은 시리즈의 논문에서 극도로 짧은 논법으로 핵심을 간결하게 하여 푸앙카레 추측을 해결했습니다. 그때 페렐만은 리처드 해밀턴이 푸앙카레의 추측을 풀기 위한 프로그램을 구상했는데, 마지막에 정말로 어려운 방향을 7년간 아무도 못했지만, 그가 새로운 기법을 도입해서 문제를 해결해냈습니다. 미국을 순회하며 문제의 해결책에 대한 강연을 했고, 그 아이디어가 어디서 왔는지 전문가가 이해할 수 있을 정도로 명확하게 설명했다고 알고 있습니다. 물론 뒤에 담긴 드라마들이 있긴 하지만, 테렌스 타오를 비롯한 수학자들이 독자적으로 그의 방법을 공부하고, 후속 클레이 연구소 보고에 따라 위원회가 구성되어 문제의 해법을 분석하여 페렐만의 아이디어에 독창성에 많은 기여를 주어 필즈메달상과 밀레니엄 상을 주려고 했습니다. 그리고 페렐만이 만들어낸 방법론은 후대에 사이먼 브렌들을 비롯한 여러 수학자가 그 방법론으로 여러 문제들을 해결하여 새로운 지평을 열었습니다.</p>

<p>그런데 이번 오픈AI가 연구한 걸 해설할 수 있는 사람은 기술적으로 어떻게 했는지를 설명할 수 있으면서, 수학적인 내용을 설명하지 못하는 촌극이 벌어졌습니다. 이게 무슨 신호를 줄 수 있는지 사회에 대한 영향력을 생각하지 않았던 것에 유감입니다.</p>

<p><span style="color: blue;">Q5. 만약 문제가 있다고 보신다면 어떤 해결이 전제돼야 할지요.</span></p>

<p>우선 현재의 평가 시스템, 저널 시스템을 개선할 수 있는 방안을 찾아야 합니다. 지금 논문이 과도하게 많이 생산되어 어떤 지식이 유의미하고 후대에게 전승될 것인지 생각하는 과정이 많이 약해지고 있다고 생각합니다. 더 우려되는 상황은 AI를 사용한 리뷰인데, 논문을 읽어보지도 않고 AI에 리뷰를 맡긴 것으로 보이는 레포트가 늘어난다는 제보가 들립니다. 이런 기본적인 연구 윤리를 위반하는 사람들에게 적절한 페널티를 주는 방안이 필요하다고 생각하는데, 어떻게 해야할지 모르겠습니다. 이러기 위해서는 평가시스템에 대한 개혁을 해야한다고 생각합니다.</p>

<p><span style="color: blue;">Q6. 이번 성명에는 지난주 나비에-스토크스 방정식 풀이 주장에 대한 윤리 논란과도 관련이 있어 보입니다. 관련해 하실 말씀이 있으실지요.</span></p>

<p>지금 OpenAI 공고문을 보고 AI에 그대로 입력해서 풀었다고 생각을 하는 사람들이 많은 것 같으나, 그렇지 않습니다. Buckmaster 성명문에도 기술되어 있듯이, 처음에는 프롬프트 엔지니어링을 안 했다고 하면서 말바꿨던 정황도 있는 상황입니다. 그리고 이 분야의 전문가중 한 분인 Javier Gomez-Serrano도 프롬프트를 어떻게 한 건지, 실험을 정확하게 어떻게 한 것인지 투명하게 공개하라고 밝힌 바가 있습니다. 이건 그냥 타이핑한다고 될 문제가 전혀 아닙니다.</p>

<p>OpenAI의 공고문에는 Cordoba, Martinez-Zoroa에 대한 언급이 어디에도 없습니다. 어디에서 아이디어가 시작되었는지 명확한 언급도 없고, 이 연구를 진행할 때 감독한 사람들이 누구인지도 모릅니다. 그리고 9월 1일에 Alpoge와 Buckmaster가 연구하고 있다는 소문을 듣고 ChatGPT의 내부 머신을 바탕으로 막대한 리소스를 동원해서 문제를 풀었습니다. 그리고 그 검증의 책임은 Lean 파일 올린 것으로 충분하다고 주장하고 넘긴 상태입니다. 더불어 제가 앞에서 말한 연구의 흐름들이 있는데, 이는 수리유체역학 연구의 배경들을 고려하면 절대로 빠질 수 없는 이름들입니다. 그러나 이 연구 결과에 대해서는 하나도 언급이 없다는 건, 이 실험을 감독한 사람이 이 분야의 전문가는 아니라는 걸 보여줍니다. 첫 드래프트에서는 아예 Cordoba, Martinez-Zoroa 자체는 언급도 되지 않았습니다. 그만큼 이 실험 과정에서 어디서 아이디어가 왔는지, 무엇에서 온 것인지 안에서조차도 인지 못했다는 겁니다. 제일 황당한 것은 이 논문의 말미에서 점성계수 rescaling하는 부분인데, 이건 수리유체역학 전문가라면 너무 당연한 것이라 설명조차 안하는 걸 채워넣은 겁니다. 논문을 마무리하는 단계에서 이걸 빼지도 않았다는 건, 수리유체역학 전문가가 전혀 없었다는 걸 반증하는 겁니다.</p>

<p><span style="color: blue;">Q7. 그 외에, 이번 선언에는 언급되지 않았지만 추가적으로 수학계가 인공지능과 관련해 고민해야 할 문제는 무엇일지요.</span></p>

<p>이번 선언문에서는 OpenAI의 윤리 문제에 대해서는 일부러 언급하진 않은 것 같습니다. 실험과정에서 고객의 데이터를 활용했을지도 모른다고 인정을 한 만큼, 과연 공개 과학의 발전이 과연 얼마나 이뤄질 수 있는지는 매우 우려스럽습니다. 수학 학회장, 특히 제가 미국에서 본 것 중 좋았던 것은 각자가 아직 완벽하지 않아도 어느 정도의 연구 결과를 들고와서 신뢰할 수 있는 사람들 앞에서 아이디어를 공유하며 더 좋은 방향으로 나아가는 모습을 볼 때였습니다. 수학에서도 이런 문화가 사라질 수도 있어 아깝습니다.</p>

<p>저는 지금은 LLM을 사용해서 수학 연구를 진행하진 않지만, LLM을 사용한 연구는 근 시대에는 피할 수 없는 흐름이 될 거라고 생각합니다. 더불어서 LLM을 사용하지 않으면서 연구를 진행한 사람들에 대한 존중이 언제까지 이뤄질 수 있을지에 대한 걱정도 있습니다. 현재 테크계가 수학 문제를 벤치마크로 삼아 상업적으로 자신의 모델을 홍보하는 전략은 수학 연구 분야를 황폐화시키는 상황을 만들고 있다고 생각합니다. 더불어서 이 LLM을 사용해서 각종 반례들을 생산해서 수학저널이 지금 심사할 수 없을 정도로 논문이 과도하게 만들어진 상황에 대한 고민을 해야하는 상황이라고 생각합니다. 저는 제 머리가 조금 퇴화되는 느낌도 있었지만, 이런 문제 때문에 잠시라도 LLM을 수학 연구에 활용하고 있지 않습니다.</p>

<p>지금 이 상황은 저는 오리알이 몸에 좋다고 오리알을 다 먹어서, 다음 오리알을 낳을 수 있는 오리를 다 죽이고 있는 상황이라고 생각합니다. Proof and Prompt를 비롯해서 국내에서도 수학자들과 다른 인접분야의 연구자들이 이 문제를 머리를 맞대어 토론하고 해결해야 한다고 생각합니다.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[I got a request to share an expert opinion through the Science Media Center Korea on ‘A Severe Misalignment of AI in Mathematics’ given at https://mathandai.org/.]]></summary></entry><entry><title type="html">My recent thought on generative AI to mathematics, changed my stand</title><link href="https://willkwon-math.kr/2026/08/28/declare.html" rel="alternate" type="text/html" title="My recent thought on generative AI to mathematics, changed my stand" /><published>2026-08-28T10:00:40+00:00</published><updated>2026-08-28T10:00:40+00:00</updated><id>https://willkwon-math.kr/2026/08/28/declare</id><content type="html" xml:base="https://willkwon-math.kr/2026/08/28/declare.html"><![CDATA[<p>As you could see in my previous post, I was relatively positive about generative AI for the potential discovery of mathematical results, and I do not hide the fact that I used generative AI (Gemini and Claude) sometimes to get some intuitions or background study, or to generate simulations for better presentations. Mostly, I have used generative AI so far to</p>

<ol>
  <li>prepare teaching materials to provide better learning experiences (historical survey);</li>
  <li>get some structural feedback first on an essay;</li>
  <li>understand basic research languages on different research areas;</li>
  <li>understand the nuances of English expression (break language barrier);</li>
  <li>feedback on my thoughts;</li>
  <li>find some good explanations or some proofs on mathematics related to my area (some lemma level)</li>
  <li>generate a numerical simulation (for presentation or to get initial intuition).</li>
</ol>

<p>Hence I had several good reasons so far to use generative AI as a researcher to expand my knowledge outside my realm, but I gradually changed my mind when I read OpenAI’s announcement on the ‘resolution’ of the 10 problems and kept reading arXiv posts on the declaration of AI usage in preprints these days by different authors. While authors’ declaration on AI use is ethical, it is too awkward for me to see why we mathematicians promote AI models, not just mention AI usage. That started to change my mind, and the problem is that it is gradually breaking down the mathematics community. Currently, we are in a flood of mathematics papers, and the journal system is breaking down.</p>

<p>I had several attempts to find a potential approach to solve a problem using generative AI. Some of them were good, and I liked it before, while I think that I can find a way to prove it without using AI. I declare that I did not get satisfactory results on this activity. Maybe I could do prompt engineering better but I did not want to do it. I liked how I could plot some numerical simulations via Claude code first, and gradually ask my colleague how I could interpret this. Furthermore, I could taste some research area that I had interested in (like computer assisted proof, numerical analysis).</p>

<p>However, after reading these articles, I had changed my mind and I think we need to focus more on the mathematics community.</p>

<ul>
  <li><a href="https://tasmin.substack.com/p/mathematicians-need-to-act?utm_campaign=post-expanded-share&amp;utm_medium=web">Tasmin Chu, Mathematicians need to act</a></li>
  <li><a href="https://arxiv.org/abs/2608.02859">Max Weinreich, the crisis of AI-generated mathematics</a></li>
  <li><a href="https://siliconreckoner.substack.com/p/theres-this-like-massive-exogenous">Michael Harris, “there’s this like massive exogenous force” haunting mathematics, No, the Leiden Declaration is not a “public cry for help!”
</a></li>
  <li><a href="https://ai-ethics.kr/ai-scientist/">Do we need to generate scientific knowledge fast and a lot? (Korean): 지식도 더 빨리, 많이 만들면 되지 않나요</a></li>
  <li><a href="https://ai-ethics.kr/education-in-the-age-of-ai-2026-06-22/">Where is education in the age of AI agent? (Korean): AI 행위자 시대에 교육은 어디에 서 있을까요</a></li>
</ul>

<p>My current stand aligns with the paragraph “What could an ethical model of using AI in mathematics look like?” in Tasmin’s article. We might need to discuss this matter more seriously. The education system is breaking down, and the journal system is breaking down. I believe that those are not good for the humanities and mathematics community.</p>

<p>I have used generative AI from multiple perspectives: schedule controller, data collection, generating numerical simulations, coding problems, literature surveys from different disciplines, and some historical texts that I cannot read in an article, say, French. All of those are for my convenience to track potential mistakes and to deliver key ideas in mathematics to a broader audience better. I believe that this is for better understanding to the audience.</p>

<p>However, we are facing lots of danger to our community’s safety. The purpose of mathematics is not to prove many theorems and solve problems. It is for better understanding how our world works and to find a better perspective on research problems. This also aligns with the reason that I recently worked on the Muskat problem and kinetic equations. For me, those problems will help to find a good perspective to understand our world.</p>

<p>I was gradually used to generative AI as an early adopter, so it is hard to cut it down at once. From now on, I will not use generative AI for my mathematics research unless we find a way to keep the mathematics community vibrant. I don’t know how many days I will keep this oath for long times yet. However, I think raising an issue would be important at this moment.</p>

<p>My point of view seems naive since I have no better alternative. This new technology changes our life, and there is no turning back. However, refraining from alternative ideas dilutes the problem that we are facing. So we need to think about keeping us from potential dangers by finding issues and finding a way to keep our community.</p>

<p>I have several mixed feelings these days and some of my colleagues try to find a way to make it better. We will see very soon.</p>

<p>Add: 08/29 It is worth to read</p>
<ul>
  <li><a href="https://proofsandprompts.com/2026/08/14/a-viewpoint-on-the-ai-dissenter-viewpoint/">Giorgio Mangioni, A viewpoint on “The AI dissenter viewpoint”</a>.</li>
  <li><a href="https://proofsandprompts.com/2026/08/28/the-ai-assisted-mathematicians-dilemma/">Ruodu Wang, The AI-assisted mathematician’s dilemma</a></li>
  <li><a href="https://borretti.me/article/mathematics-without-mathematicians">Fernando Borretti, Mathematics Without Mathematicians</a></li>
  <li><a href="https://tasmin.substack.com/p/more-calls-to-action-for-the-mathematical">Tasmin Chu, More calls to action for the mathematical community</a></li>
</ul>

<p>I am more or less similar stand with Professor Duminil-Copin.</p>
<ul>
  <li><a href="https://proofsandprompts.com/2026/08/30/care-for-a-little-more-ai/">Hugo Duminil-Copin, Care for a little more AI?</a></li>
</ul>

<p>In definite future, if we find a better way, I am more similar position to</p>
<ul>
  <li><a href="https://birdsnfrogs.github.io/2026/09/12/Felix_qui_potuit_rerum_cognoscere_causas.html">Nestor guillen, Happy, those able to know the causes of things</a></li>
</ul>

<p>I am not fully against the potential possibility of using generative AI. However, the problem is how to find a way to keep our math research community vibrant. At least, I am glad that we have a forum to discuss in a lengthy way.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[As you could see in my previous post, I was relatively positive about generative AI for the potential discovery of mathematical results, and I do not hide the fact that I used generative AI (Gemini and Claude) sometimes to get some intuitions or background study, or to generate simulations for better presentations. Mostly, I have used generative AI so far to]]></summary></entry><entry><title type="html">Sarah Helen Whitman, who saved Edgar Allen Poe</title><link href="https://willkwon-math.kr/2026/03/08/woman.html" rel="alternate" type="text/html" title="Sarah Helen Whitman, who saved Edgar Allen Poe" /><published>2026-03-08T10:00:40+00:00</published><updated>2026-03-08T10:00:40+00:00</updated><id>https://willkwon-math.kr/2026/03/08/woman</id><content type="html" xml:base="https://willkwon-math.kr/2026/03/08/woman.html"><![CDATA[<p>An original version is Korean and is given in the <a href="https://brunch.co.kr/@skykite9/57">link</a>. The following translation is based on Claude with some minor modification.</p>

<p>Today, March 8th, is International Women’s Day. It originated in demonstration of the tens of thousands of textile workers who took to the streets of New York in 1908, though why March 8th specifically became the designated date remains unclear. It’s a history less than 120 years old, yet even the origins of how this day was established aren’t widely known.</p>

<p>This is a story from my time dating someone in Providence, someone I’m no longer in contact with. She loved horror movies, and she recommended Netflix’s “The Fall of the House of Usher” to me. I later discovered the story was written by Edgar Allan Poe, and it wasn’t until a year had passed that I learned how deeply connected Poe was to Providence.</p>

<p>After moving into my current apartment, I found that the library near my house was one where Edgar Allan Poe had once lectured, and it was the first time that I heard the name Sarah Helen Whitman as Poe’s lover. In her time, Whitman was a well-regarded literary critic, while Poe was a writer only beginning to gain recognition across America through his poem “The Raven”, just a year before his death. The two became engaged, but various circumstances led to the engagement being broken off, and Edgar died in the street a year later.</p>

<p>Poe did not achieve popular success until he was 36. American literature at the time was dominated by transcendentalism — figures like Ralph Waldo Emerson — and by Puritan-centered writing. His novels written around his thirties, “Ligeia” and “The Fall of the House of Usher”, went largely unnoticed in their day, and he could not sustain himself financially through fiction alone. But once “The Raven” brought him success, he began receiving invitations to speak at literary salons.</p>

<p>Frances Osgood, who had frequent exchanges with Poe, invited him to Providence. She intended to introduce him to Whitman, already a celebrated writer and literary critic in New England, but as the story goes, Edgar caught sight of Whitman standing in a rose garden from a distance and could not bring himself to speak to her. Yet Whitman had been reading his work four or five years before he became famous, and as a tribute to him, she wrote a Valentine’s Day poem praising his artistic sensibility.</p>

<p>Whitman was born and raised in Providence, and was the prominent literary figures of literature circles in New England in her era. She was close with Ralph Waldo Emerson and described herself as his disciple, so great was his influence on her. She corresponded with Margaret Fuller, who wrote what is considered one of the first works of feminist literature, and served as vice president of the Rhode Island Woman Suffrage Association.</p>

<p>She contributed more than 80 essays to newspapers. In 1849, Rufus Griswold, the most influential literary editor of the day, included Whitman as a representative American female poet in his anthology, even singling her out in his preface. Horace Greeley, founder of the New York Tribune, also sought her contributions, leaving no doubt that she was a prominent literary figure of her time.</p>

<p>When Edgar Allan Poe died in 1849, Griswold published an obituary in the newspaper under the pseudonym “Ludwig,” portraying Poe as a drunkard, a fraud, and a man of ruined character. Griswold had been designated as the editor of Poe’s posthumous works, ironically, by Poe himself, and the preface to Poe’s collected works contained a deeply distorted biography. From that point on, Whitman wrote a book in defense of Poe’s work, and after Griswold’s own death, she produced a masterful piece logically refuting all charges against Poe’s literary merit. Yet 160 years later, Whitman is remembered only as Edgar Poe’s former fiancée. What is spoken of are the letters they exchanged, their fateful meeting, and the turbulent dissolution of their engagement, while the 17 years she spent working to restore Poe’s reputation within American literary circles go largely unnoticed.</p>

<p>Edgar Poe and His Critics, written in 1860, reads even today as a work of remarkable logical precision, one that hardly feels 160 years old. It directly refutes Griswold’s 1849 exposé as a text filled with distorted facts and malicious assumptions. To accomplish this, Whitman gathered information from contemporaries who had known Poe, added her own critical insights, and argued methodically for why Poe’s work deserved serious attention.</p>

<p>Critics of the time praised his facility with language but refused to recognize the artistic merit of his work, unsurprising given that the prevailing moralism of Puritan culture made it nearly impossible for gothic horror fiction to find its light. <a href="https://www.eapoe.org/papers/misc1851/18600000.htm">In this essay</a>, Whitman articulates the value of such literature as “a product of deep inner experience and the projection of intense imagination,” writing with measured scholarly calm rooted in her personal memories. She squarely refutes the charge that Poe lacked moral sensibility by drawing on his past work as evidence, and writes with quiet empathy about the drinking that had led to their broken engagement, approaching it from his perspective.</p>

<p>In writing this, Whitman referred to herself as “one of the friends who remembers him,” crafting a precise and deliberate piece so that future generations might judge Poe’s genius fairly. The essay is also regarded as the first work to logically separate an author’s private life from the artistic integrity of their work, a distinction made before Oscar Wilde, and a full 80 years before Roland Barthes argued that a work’s meaning is completed in the moment a reader encounters it, regardless of the author’s intent.  It is a distinguished piece of writing that steps beyond the “biographical criticism” that dominated the era and argues, with clear logic, why Poe should not be undervalued.</p>

<p>In 1873, British John Ingram, outraged by Griswold’s false record, began a project to uncover the truth. As Ingram worked on a biography of Poe, he corresponded with Whitman. She provided him with Poe’s original letters and rare materials, and over five years they exchanged correspondence in which she explained and critiqued Poe’s literary theories and the circumstances of his life. Later, when Ingram realized that Whitman also corresponded with another biographer, he published another private letters as a news item, portraying Whitman in inappropriate way. She is said to have responded with a graceful critique of Ingram in the Providence Journal. The 75-year-old woman died of heart disease, complications, and ether addiction one month after writing that piece. Ingram’s biography would go on to establish Poe’s reputation in Europe as “America’s cursed genius.” Yet Whitman, whose contributions were among the greatest to that biography, is mentioned only as “Poe’s former fiancée.” The University of Virginia later commented that the collected letters contain “sharp and insightful discussions of Poe that biographers have not sufficiently utilized.” Mail correspondence can be seen in this <a href="https://www.eapoe.org/papers/misc1921/phrcv000.htm">link</a>.</p>

<p>The moment when Poe could not bring himself to speak to Whitman tends to be flattened into a simple narrative, which he didn’t approach her because she was beautiful. It is true that Poe later wrote her love letters, but at that time he was a writer only belatedly beginning to receive attention, while Whitman was already a central figure in New England’s literary social world. Yet Ingram referred to the remarkable Edgar Poe and His Critics, the very essay that made his biography of Poe possible, merely as “a charming little book.”</p>

<p>I believe this story deserves to be more widely known. To read Whitman’s 17 years of advocacy after Poe’s death as nothing more than an affectionate tribute to a last love is, I think, to diminish the full arc of her life. Seventeen years of struggle cannot be reduced to love alone. It seems to me that she used every resource available to her, as an intellectual, to defend what she believed was genuine literary value. Without Whitman’s efforts, that singular gothic fiction might well have been forgotten, which might lost to the moral solemnity of antebellum America, or swept away in the aftermath of the Civil War. I find myself wondering how this story could be shaped into something for wider audiences, and who would love it — and then I remember: today is International Women’s Day.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[An original version is Korean and is given in the link. The following translation is based on Claude with some minor modification.]]></summary></entry><entry><title type="html">Some announcement on AI: saying from Feynman, Laozi, and Larson</title><link href="https://willkwon-math.kr/2026/01/09/war.html" rel="alternate" type="text/html" title="Some announcement on AI: saying from Feynman, Laozi, and Larson" /><published>2026-01-09T10:00:40+00:00</published><updated>2026-01-09T10:00:40+00:00</updated><id>https://willkwon-math.kr/2026/01/09/war</id><content type="html" xml:base="https://willkwon-math.kr/2026/01/09/war.html"><![CDATA[<p>A Korean translation is given in the <a href="https://brunch.co.kr/@skykite9/47">link</a>. English is the original version.
This note is a draft for announcement in the following semester class.</p>

<p>Due to recent advances in generative AI, it is highly tempting to use it to solve a homework problem. Of course, I understand that you might feel it is easy to achieve a better score with AI, requiring less effort, but you also feel you are letting your brain outsource, becoming less competent than before. I think this is one of the environmental challenges we face because TikTok or YouTube Shorts weaken your concentration over time, and the weakened middle education due to COVID-19. I am also highly influenced by YouTube Shorts and Instagram Reels these days, and it is not that easy to deviate from them! I also understand that it is hard to concentrate on something more than before because there are so many tempting things that you could easily deviate from the path that you had to walk.</p>

<p>However, as a member of the teaching staff, it is my responsibility to help you get out of these trends and become who you want to be. As I talk with other students, this is not my own thinking, but you keep thinking about those concerns. I also feel that way after I use generative AI these days. I also actively use those when I want to sharpen my logic or seek some initial background, but I always double-check by reading some concrete references.</p>

<p>After ChatGPT launched, many students turned to generative AI to help them solve homework. It is totally okay to use generative AI to help your learning process, but it is not desirable to rely on those tools by letting your brain do the work for those computers. Your brain deserves to work. You should be aware of yourself, what you know, and what you don’t know. The point here is that active learning is more important than before.</p>

<p>I want to bring a famous quote from Richard Feynman: “The first principle is that you must not fool yourself, and you are the easiest person to fool. It is highly possible that you could say something that you don’t know. I found those in the advent of AI and in YouTube’s algorithm selection, which can lead to incorrect information or knowledge that is not easy to understand on that learning curve, and will give a misconception. Hence, it is more important than ever that you distinguish whether I really understand the key content or not. This lesson can also be found in an old saying from the Chinese philosopher Laozi: “To know that you do not know is the highest wisdom. To not know that you do not know is a disease. Only when one recognizes the disease as a disease can one be free from it”. In this age of AI, ‘pretending to know’ has become an easy trap to fall into, but it is a trap that prevents true growth.</p>

<p>In the last semester, I found that some students submitted homework they did not understand; for instance, imagine that elementary school students calculated the area of a triangle using calculus. This kind of logical fallacy makes it clear that the brain was not engaged. To protect the integrity of our learning community, I had to report those cases as academic misconduct. Please understand that our evaluations now depend heavily on in-person assessment; if you don’t understand the topic in your heart, you cannot pass or earn a satisfactory score if you rely solely on generative AI.</p>

<p>I know many of you have excelled in everything you have done so far. That’s why you’re here. Learning process is painful, and I am here to help you get through those difficulties. Failure will guide you to get a correct intuition to solve a problem, and discussion will lead to another big intellectual leap. I once spent three years struggling with a problem. I spent months stuck, feeling small as I watched others prove brilliant results. When I told my mentor, “It’s not working,” he gave me the most important lesson of my life. He said, “That’s good news. If it were easy, it wouldn’t be worth your time”. Failure wasn’t a waste of time. It was the process of sharpening my intuition. I still remember the moment of breakthrough. I was on a crowded metro when suddenly an abstract idea became a vivid image in my head, so I pulled out my notebook and began scribbling against the train door. That sudden flash of beauty is a human privilege that no AI can ever experience or give to you.</p>

<p>In the end, I want to ask you: what makes you distinct from generative AI? Many brilliant stories emerged from a unique idea rooted in life experiences. Frankenstein by Mary Shelley, The Fall of the House of Usher by Edgar Allan Poe, and Hamlet by Shakespeare (although the motivation is debated, the novel or movie Hamnet (2025) could offer an interesting theory) can be born from unique life experiences. Using generative AI alone will yield an average idea that is indistinguishable from any other. Mathematics is an art that captures phenomena in a rigorous, concise, and logical language. Great mathematics comes from a desire to solve or answer mysterious questions.</p>

<p>Throughout this course, I hope that you will learn something from mathematics that will help you answer those questions on your own.  Jonathan Larson, who wrote the famous Broadway musical “Rent,” said, “The opposite of war is not peace; it’s creation.” Of course, his life was to struggle against his diseases as well as financial stuff. However, we are in a war for our attention, fighting against algorithms and the temptation of shortcuts. Being quiet or passive brings an illusion of peace, and actually, peace does not solely exist. The creation is achieved by actively engaging your brain to build something that belongs only to you. I hope that this mathematics course will give you a good experience after you leave Brown.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[A Korean translation is given in the link. English is the original version. This note is a draft for announcement in the following semester class.]]></summary></entry><entry><title type="html">Art of Academic Writing: my perspective</title><link href="https://willkwon-math.kr/2025/12/06/AIwriting.html" rel="alternate" type="text/html" title="Art of Academic Writing: my perspective" /><published>2025-12-06T10:00:40+00:00</published><updated>2025-12-06T10:00:40+00:00</updated><id>https://willkwon-math.kr/2025/12/06/AIwriting</id><content type="html" xml:base="https://willkwon-math.kr/2025/12/06/AIwriting.html"><![CDATA[<p>I wrote it in <a href="https://brunch.co.kr/@skykite9/35">Korean first</a> and I rewrote it in English.</p>

<p>I cannot remember where I saw the link (probably Facebook or LinkedIn). Someone made a toolkit for writing a paper that checks references and writing at the same time. While I agree that AI could greatly shape one’s point of view, I am highly skeptical of relying on generative AI to write a paper.</p>

<p>Writing a mathematics paper is a writing between poetry and a novel. It needs to be concise, like poetry, and explained well so the reader can understand the problem’s key difficulty. Although mathematics research paper is nonfiction, it needs a sort of elegance in elaborating the logic and it should contain some logical thinking so that people can be touched.</p>

<p>Many of the great papers that I read were in that category. For instance, the famous <a href="https://arxiv.org/abs/0904.2760">Landau damping paper</a> by Mouhot and Villani clearly explains why this problem is important and elaborates on its key difficulties. Also, they explain the whole strategy for managing all difficulties. Another reason that I like this paper is that it appreciates people who discuss the problem with them. Creating a new language to explain the mysterious phenomenon can be achieved through fruitful discussions with people, not from a single brilliant mind. Moreover, this paper also explains potential different directions so that future researchers can get some benefit.</p>

<p>I also like the fundamental paper due to J. Leray written in 1934, <a href="https://arxiv.org/abs/1604.02484">Sur le mouvement d’un liquide visqueux emplissant l’espace</a>. It explains many efforts by engineers, physicists, and mathematicians to understand the motion of viscous fluids. After Navier introduced the model, J. Leray sought to justify it by introducing a new framework. This is now called the theory of weak solutions. In this paper, he proved the global existence of turbulent solutions (now it is called the Leray-Hopf weak solution). To show this, he invented a revolutionary idea to construct a weak solution. Not only for constructing this solution, but he also investigated a limitation of this solution by introducing an epoch of regularity. While this paper was written 90 years ago, I can see how he thought about this problem, and his perspective amuses me. Modern PDE theory did not deviate that much from this paper.</p>

<p>I heard that someone created a review website for an AI paper from Stanford. If the user uploads the paper as a PDF, the AI will evaluate it and provide feedback. <a href="https://paperreview.ai">Link</a></p>

<p>It seems this tool was created because publishing a paper on AI is too competitive. I don’t know how to think. I believe that humankind chose to be destructive. Now we have lost lots of critical thinking, and many writings have become homogeneous.</p>

<p>90% of research papers will be forgotten. Many people will not listen to how to write a good paper in the extreme era of publish-or-perish.</p>

<p>Now I kept thinking how to write a good article to touch the reader. That’s why I kept reading literature these days to get some idea.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[I wrote it in Korean first and I rewrote it in English.]]></summary></entry><entry><title type="html">College Education in the advent of Generative AI</title><link href="https://willkwon-math.kr/2025/11/27/AI.html" rel="alternate" type="text/html" title="College Education in the advent of Generative AI" /><published>2025-11-27T21:00:40+00:00</published><updated>2025-11-27T21:00:40+00:00</updated><id>https://willkwon-math.kr/2025/11/27/AI</id><content type="html" xml:base="https://willkwon-math.kr/2025/11/27/AI.html"><![CDATA[<p>The original article is written in Korean by myself <a href="https://brunch.co.kr/@skykite9/33">Link</a>. I put the translation generated by Claude.
I polished some word choice which generative AI cannot translate properly.</p>

<p>I will try to rewrite this article in the future within December.</p>

<p>Since ChatGPT emerged three years ago, GenAI has made remarkable progress and has deeply influenced at least university education. I believe fundamental changes in the traditional education system are necessary, but there doesn’t seem to be much discussion about what direction we should take. In this essay, I want to organize my thoughts on the direction university-level education should pursue.</p>

<p>Let’s imagine writing a novel based on the emotion of fear. I tried it with Gemini. I entered the prompt: “I want to write a horror novel. What suggestions would you make for initial settings or a draft?” Gemini replied that the main character should be an ordinary person readers can empathize with, and when they face an abnormal horror situation, readers should also feel fear. Additionally, I should give the main character a fatal weakness or flaw. Finally, I must define the object of fear, and the object of fear (monster, ghost, curse, etc.), but I should not be described in detail.</p>

<p>The first answer AI produces from a prompt is, as expected, average and predictably structured. However, works that transcend their era—novels that people still read 200 years later—don’t fit the structure Gemini suggested. Around 1817, at Byron’s villa, while Percy Shelley and Claire Clairmont were trying to break the monotony of rainy days, the idea came up to write horror stories. Mary struggled to write a novel because of a lack of inspiration, but eventually wrote one after an interesting dream. It was called “Walking Dream,” now known as Frankenstein. Though written 200 years ago, it’s the first science fiction novel, and rather than being analyzed merely as fantasy, it’s a novel beloved to this day for raising many questions, adapted into plays and, recently, into films.</p>

<p>While we could speak of this novel’s originality in many ways, taking the theme of “horror” and extracting “the primal emotions of pain and loneliness when a new life form created by science and technology is abandoned at birth, struggles in that abandonment, tries to assimilate into society but isn’t accepted because of its appearance”. This is the discovery of subject matter that transcends average knowledge and thinking. I believe this became a great novel that continues to raise many questions today, thanks to Mary Shelley’s life journey.</p>

<p>Current mathematics education at universities has a structure of introducing definitions, proving them, advancing through examples, checking one’s knowledge, and moving forward by solving practice problems as assignments. Incidentally, this educational composition became established about 70 years ago; in the past, students read without practice problems, understanding between the lines of the text and creating their own examples. However, with the universalization of university education and the development of engineering, the need to solve concrete practical problems emerged, and I understand that this led to the establishment of current teaching methods. However, the birth of generative AI is shaking the foundation of this long-standing educational system. The practice-problem method of evaluating students turns out to be ineffective and it becomes problematic. In other words, the foundation of the educational system, knowledge verification and proficiency evaluation through homework, has been shaken.</p>

<p>So how should we solve this problem? We must now always assume AI usage. Therefore, I think attempting to block it entirely is an idea that goes against the times. While there are negative effects, education’s goal should be to maximize positive impacts and enable future generations to develop better ideas. GenAI is a new era’s search tool. Documents written in French or Russian are now more accessible, and when preparing classes, I can quickly research unfamiliar historical contexts, so I can deliver lectures that are more engaging for students. When writing papers and studying other papers, GenAI helps roughly grasp core ideas and kindly explains parts that are so basic I’m afraid to ask about, filling knowledge gaps. Despite these advantages, insisting only on past systems is no different from arguing that we should return to calculator-era exams because computers ruin students.</p>

<p>How was Mary Shelley able to write such a novel? Mary had intellectual soil that allowed access to much knowledge, studying literature and science by reading many books in her library under her open-minded father and mother, and she could write a novel inspired by Galvanism, which was popular in the late 18th century. With Galvani’s successful experiment of moving dead animal muscles using electricity, she could conceive the idea of creating life with electricity for Frankenstein’s birth. Additionally, she could write such a novel thanks to her husband, Percy Shelley’s, support. In 1800, women’s status was significantly lower than it is now, making it difficult to publish novels under one’s own name. Having someone who can support you gives great strength in taking on new challenges.</p>

<p>So how should university education proceed? We need to care more about students and stop viewing them merely as objects of evaluation. To do this, we need an era that pays more attention to students, especially those with a passion for learning, by focusing on how students can acquire new perspectives and understand more effectively. We must remind students who simply use AI to get answers and grades that they’re wasting their time. If they use knowledge not taught in class, they should be severely punished, but we shouldn’t discourage the attitude of trying to learn new knowledge by using AI to write their answers more perfectly.</p>

<p>However, as a practical matter, in the case of basic mathematics courses, it’s true that if these courses are shaken, there will be great difficulty in digesting other science and engineering classes. For this reason, for basic courses only, it may be necessary to change the system to periodic problem-solving assignments, build basic stamina through handwriting, and evaluate through quizzes. Additionally, during that process, AI supports repetitive learning, and instructors use the saved time to provide customized guidance to where students are stuck. This is the direction university education should head in the next 10 years. Now we need to focus on how we can teach those who could ask a daring question.</p>

<p>Since students in American universities are absent so often, I don’t know how to solve this. However, universities must now pay more attention not to the simple transmission of knowledge, but to the role of laying intellectual groundwork so that new imagination can unfold.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[The original article is written in Korean by myself Link. I put the translation generated by Claude. I polished some word choice which generative AI cannot translate properly.]]></summary></entry><entry><title type="html">Blashcke-Santalo inequality and Aleksandrov estimates</title><link href="https://willkwon-math.kr/2025/10/23/Alexandrov.html" rel="alternate" type="text/html" title="Blashcke-Santalo inequality and Aleksandrov estimates" /><published>2025-10-23T10:00:40+00:00</published><updated>2025-10-23T10:00:40+00:00</updated><id>https://willkwon-math.kr/2025/10/23/Alexandrov</id><content type="html" xml:base="https://willkwon-math.kr/2025/10/23/Alexandrov.html"><![CDATA[<p>Yesterday, while I am attending ICERM conference on <a href="&quot;https://icerm.brown.edu/program/hot_topics_workshop/htw-25-fdt&quot;">fluid dynamics and turbluence</a>, I learned from <a href="&quot;https://www.ndguillen.com/&quot;">Nestor</a> that there is another way to look at the Aleksandrov maximum principle via convex geometry.
I appreciate his passion for sharing this knowledge with me.</p>

<p>In my previous blog post, <a href="&quot;https://willkwon-math.kr/2022/07/31/Amax&quot;">Aleksandrov estimate</a> plays an important role in regularity theory for equations in nondivergence form or fully nonlinear equations. For simplicity, we consider a convex function $h:D\rightarrow\mathbb{R}$ defined on a convex body $D$ satisfying $h=0$ on $\partial D$. Furthermore, we assume that the center of mass of $D$ is the origin. A classical Aleksandrov estimate is that</p>
<div>
\begin{equation}
\Vert h \Vert_{L^\infty(D)} \leq C_d|D|^{1/d}|\nabla h(D)|
\end{equation}
for some constant $C_d&gt;0$.
</div>

<div>
There is an interesting connection with Blashcke-Santalo inequality and this estimate. To state this, let us define the polar dual
\begin{equation*}
D^*=\{x\in\mathbb{R}^d : x\cdot y \leq 1\quad \text{for all } y \in D\}.
\end{equation*}
In 1939, Mahler proved that 
\begin{equation*}
4^n (n!)^{-2}\leq  |D| |D^*|\leq 4^n.
\end{equation*}
Later, Santalo proved that the upper bound has a precise geometric bound
\begin{equation*}
|D| |D^*|\leq |B_d|^2,
\end{equation*}
where $B_d$ is the $d$-dimensional unit ball. The inequality becomes equality when $D=B_d$. After this work, several interesting improvements were made to determine the precise lower bound for $|D| |D^*|$. I do not have a clear picture of how researchers could obtain optimal estimates by using the geometry of Banach spaces (this is slightly unclear to me). Bourgan-Milman proved the following estimate, which is now called Blashcke-Santalo inequality.
</div>

<p>ongoing….</p>]]></content><author><name></name></author><summary type="html"><![CDATA[Yesterday, while I am attending ICERM conference on fluid dynamics and turbluence, I learned from Nestor that there is another way to look at the Aleksandrov maximum principle via convex geometry. I appreciate his passion for sharing this knowledge with me.]]></summary></entry><entry><title type="html">Smoothing estimate for heat equation with compactly supported initial data</title><link href="https://willkwon-math.kr/2025/01/09/smoothing.html" rel="alternate" type="text/html" title="Smoothing estimate for heat equation with compactly supported initial data" /><published>2025-01-09T21:00:40+00:00</published><updated>2025-01-09T21:00:40+00:00</updated><id>https://willkwon-math.kr/2025/01/09/smoothing</id><content type="html" xml:base="https://willkwon-math.kr/2025/01/09/smoothing.html"><![CDATA[<p>Today, I learned from <a href="https://www.math.ucdavis.edu/~sameer/">Sammer</a> the following technique in the <a href="https://scgp.stonybrook.edu/archives/44203">winter school</a> held at Stony Brook University. For beginner, I decide to give a detailed proof as possible I can (although some argument can be omitted in a professional level). The motivation of this calculation can be found in the recent paper due to <a href="https://arxiv.org/pdf/2405.19233">Bedrossian-He-Iyer-Wang</a>.</p>

<div>
Let us consider 
\begin{equation}
\partial_t u- u_{xx}=0\quad \text{in } (0,\infty)\times \mathbb{R},\quad u=u_0\quad \text{on } \{t=0\}\times \mathbb{R}.
\end{equation}
It is well-known that if $u_0 \in L^2(\mathbb{R})$, then the solution $u$ is instantaneously smooth for $t&gt;0$. However, the solution does not have good norm control in derivatives. However, if we assume that the initial data has a compact support, say $\mathrm{supp}\, u_0 \subset (-1/4,1/4)$, then we can show that 
$$ u\in L^{\infty}(0,\infty;L^{2}((-2,2)^c). $$
</div>

<div>
To show this, we first recall the global estimate for the heat equation:
\begin{equation}
\int_{\mathbb{R}}|u(t,x)|^2\,{dx}+2\int_0^t \int_{\mathbb{R}} |\partial_x u(t,x)|^2 \,dx=\int_{\mathbb{R}} |u_0(x)|^2 \,dx.
\end{equation}
</div>

<div>
Choose a cut-off function $\chi$ so that $\chi=1$ in $(-1,1)$ and $\chi=0$ outside $(-2,2)$. For $h\neq 0$, define $u_h(t,x) = (u(t,x+h)-u(t,x))/h$. Then $u_h$ satisfies 
$$ \partial_t (u_h)-(u_h)_{xx}=0\quad \text{in } (0,\infty)\times \mathbb{R},\quad u_h=(u_0)_h\quad \text{on } \{t=0\}\times \mathbb{R}. 
$$
</div>

<div>
Choose $\chi$ so that $0\leq \chi\leq 1$, $\chi=0$ in $(-1,1)$, and $\chi=1$ on $(-2,2)^c$. Multiplying $u_h \chi$ and taking integration by part, we get 
\begin{equation}
\begin{aligned}
&amp;\frac{1}{2}\int_{\mathbb{R}} |u_h(t)|^2 \chi \,dx + \int_0^t \int_{\mathbb{R}} |\partial_x (u_h)|^2 \chi \,dx ds \\
&amp;=\frac{1}{2}\int_0^t \int_{\mathbb{R}} |u_h|^2 \chi'' \,dxds+\frac{1}{2}\int_{\mathbb{R}} |u_h(0)|^2 \chi\,dx.
\end{aligned}
\end{equation}
For sufficiently small $h$, we note that $u_h(0,x)\chi(x)=0$ since $\mathrm{supp}\, u_0 \subset (-1,1)$ and $\chi=0$ on $(-1,1)$. Hence it follows that
$$ \frac{1}{2}\int_{\mathbb{R}} |u_h(0)|^2 \chi\,dx=0.$$
Hence by a method of finite difference, we get 
$$ \int_{\mathbb{R}} |u_x|^2 \chi \,dx+\int_0^t \int_{\mathbb{R}} |\partial_{xx} u|^2 \chi \,dxds \leq C \int_0^t \int_{\mathbb{R}} |u_x|^2|\chi''| \,d{x}ds. $$
Moreover, it follows from the energy estimate that 
$$ \int_{\mathbb{R}} |u_x(t)|^2 \chi \,dx+\int_0^t \int_{\mathbb{R}} |\partial_{xx} u|^2 \chi \,dxds \leq C \int_{\mathbb{R}} |u_0|^2 \,d{x}. $$
Hence it follows that $u \in L^\infty((0,\infty);H^1((-2,2)^c))$. Then by induction, we can further show that $u\in L^\infty ((0,\infty);H^k((-3,3)^c))$ for any $k$. 
</div>

<div>
In fact, we can obtain better smoothing estimate. It belongs to Gevrey $1/s$-class $G^s$ for $0&lt;s&lt;1$ outside $(-1/2,1/2)$. Choose the following parameters 
$$ x_1 = \frac{3}{8},\quad x_{n+1}=x_n+\frac{c_\sigma}{n^{1+\sigma}},\quad y_n = x_n + \frac{c_\sigma}{100 n^{1+\sigma}},$$
where the constant $c_\sigma$ is chosen so that $c_\sigma \sum_{n=1}^\infty \frac{1}{n^{1+\sigma}}&lt;1/8$. Define $\chi_n$ so that $\chi_n(y)=0$ for $-x_n&lt;y&lt;x_n$, and $\chi_n(y)=1$ for $\{-\infty&lt;y&lt;-y_n\}\cup \{y_n&lt;y&lt;\infty\}$ for $n\geq 1$. Then note that 
$$ \bigcap _{n=1}^\infty \{x_n=1\}\supset \left(-\infty,-\frac{1}{2}\right)\cup\left(\frac{1}{2},\infty\right),$$
$$ \mathrm{supp}\, (\nabla^k \chi_{n+1})\subset \{\chi_n=1\},$$
and 
$$ |\partial_x^j \chi_n|\leq C n^{j(1+\sigma)} \chi_{n-1}.$$
Following a similar argument, we get 
$$ \frac{d}{dt}\int_{\mathbb{R}} |\partial_x^{n+1} u|^2 \chi_{n+1}^2 dy + 2\int_{\mathbb{R}} |\partial_x^{n+2} u|^2 \chi_{n+1}^2 dy=\int_{\mathbb{R}} |\partial_x^{n+1} u|^2 \partial_x^2 (\chi_{n+1}^2)\,dx.$$
We will show that 
$$ \sum_{n=0}^\infty \left(\frac{1}{n!}\right)^{2/s} \Vert{\partial_x^n u}\Vert_{L^2}^2&lt;\infty.$$
</div>

<div>
Note that 
$$  \partial_y^2 (\chi_{n+1}^2)\leq C (n+1)^{2(1+\sigma)}\chi_n^2.$$
So it follows that 
\begin{equation}
\begin{aligned}
&amp;\int_{\mathbb{R}}|\partial_x^{n+1} u(t)|^2 \chi_{n+1}^2 d{x}+\int_0^t \int_{\mathbb{R}}|\partial_x^{n+2}u|^2 \chi_{n+1}^2 dxds\\
&amp;\leq C(n+1)^{2(1+\sigma)}\int_0^t \int_{\mathbb{R}}|\partial_x^{n+1}u|^2 \chi_n^2 dxds.
\end{aligned}
\end{equation}
 Since $\sigma&lt;1/s-1$, it follows that
\begin{equation}
\begin{aligned}
&amp;\left(\frac{1}{(n+1)!}\right)^{2/s}\int_{\mathbb{R}}|\partial_x^{n+1} u(t)|^2 \chi_{n+1}^2 d{x}+\left(\frac{1}{(n+1)!}\right)^{2/s}\int_0^t \int_{\mathbb{R}}|\partial_x^{n+2}u|^2 \chi_{n+1}^2 dxds\\
&amp;\leq C\left(\frac{1}{n!}\right)^{2/s}\int_0^t \int_{\mathbb{R}}|\partial_x^{n+1}u|^2 \chi_n^2 dxds.
\end{aligned}
\end{equation} 
</div>

<div>
If we set 
\begin{equation}
\begin{aligned}
a_n &amp;=\int_{\mathbb{R}}|\partial_x^{n} u(t)|^2 \chi_{n}^2 d{x},\\
b_n &amp;=\int_0^t\int_{\mathbb{R}}|\partial_x^{n+1} u|^2 \chi_{n+1}^2 d{x}ds,
\end{aligned}
\end{equation} 
then by induction, we have 
$$ b_n \leq C^n (n!)^{2(1+\sigma)}\Vert b_0\Vert_{L^2} $$
and so 
$$ \sum_{n=0}^\infty \left(\frac{1}{(n+1)!}\right)^{2/s}a_{n+1} \leq \Vert{b_0}\Vert_{L^2} \sum_{n=0}^\infty C^n \left(\frac{1}{n!} \right)^{2/s-2(1+\sigma)} .$$
Since $2/s-2(1+\sigma)&gt;0$, the series converges. This implies that 
$$ \sum_{n=0}^\infty \left(\frac{1}{n!}\right)^{2/s}\int_{(-1/2,1/2)^c} |\partial_x^n u(t)|^2 dx&lt;\infty.$$
Hence $u$ belongs to $L^\infty(0,\infty;G^{s}((-1/2,1/2)^c))$. 
</div>

<p>As we can see, the above argument does not work if $s=1$.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[Today, I learned from Sammer the following technique in the winter school held at Stony Brook University. For beginner, I decide to give a detailed proof as possible I can (although some argument can be omitted in a professional level). The motivation of this calculation can be found in the recent paper due to Bedrossian-He-Iyer-Wang.]]></summary></entry><entry><title type="html">Lower bound for $L^2$ norm of second-order polynomials on a ball</title><link href="https://willkwon-math.kr/2024/10/05/estimate-integral.html" rel="alternate" type="text/html" title="Lower bound for $L^2$ norm of second-order polynomials on a ball" /><published>2024-10-05T10:00:40+00:00</published><updated>2024-10-05T10:00:40+00:00</updated><id>https://willkwon-math.kr/2024/10/05/estimate-integral</id><content type="html" xml:base="https://willkwon-math.kr/2024/10/05/estimate-integral.html"><![CDATA[<p>The following calculation seems quite elementary but it is a bit hard to find it anywhere. However, I need to do it because of new paper.</p>

<div>
Set 
$$  \phi(r,X_0)=\sup_{t\in (t_0-r^2,t_0)} \frac{c}{r^2}\left(\frac{1}{|B_r|}\int_{B_r(x_0)} |u(t,x)-q_{X_0,r}(x)|^2 \,d{x}\right)^{1/2} $$
for some $q_{X_0,r}(x)=a_{X_0,r}+ b_{X_0,r} \cdot (x-x_0) + (x-x_0)^T C_{X_0,r}(x-x_0)$. 
  </div>

<p>If we take</p>
<div>
\begin{equation}
\begin{aligned}
 q_{X_0,r}-q_{X_0,\kappa r} &amp;= (a_{X_0,r}-a_{X_0,\kappa r}) + (b_{X_0,r}-b_{X_0,\kappa r})\cdot (x-x_0)\\
 &amp;\quad+ (x-x_0)^T (C_{X_0,r}-C_{X_0,\kappa r})(x-x_0),
\end{aligned} 
\end{equation}
</div>
<p>then a change of variable reduces the problem into</p>
<div>
$$ \frac{c}{r^2} \left(\frac{1}{|B_r|}\int_{B_r(x_0)} |q(x)|^2 \,d{x}\right)^{1/2}=\frac{c}{r^{d/2+2}} \left(\int_{B_r}\left|a+b\cdot y + y^T Ay\right|^2 \,d{y}\right)^{1/2}. $$  
</div>
<p>Let</p>
<div>
$$  q(x)=a+ b\cdot x + x^T A x. $$
</div>
<p>Then we claim that</p>
<div>
$$ \frac{c}{r^2}\left(\frac{1}{|B_r|}\int_{B_r} |q(x)|^2 \,d{x}\right)^{1/2}\geq c |A|.$$
</div>
<p>Note that</p>
<div>
\begin{equation}
\begin{aligned}
\left|a+b\cdot y + y^T Ay\right|^2&amp;=a^2 + (b\cdot y)^2 +|y^T A y|^2 \\
&amp;\quad+2 a (b\cdot y) + 2a(y^T Ay)+2(b\cdot y) y^T A y.
\end{aligned} 
\end{equation}
Using polar coordinates and oddness of $(b\cdot y)$ and $2(b\cdot y)y^T Ay$, we have 
\begin{equation}
\begin{aligned}
&amp;\int_{B_r} |a + b\cdot y + y^T A y|^2 \,d{y}\\
&amp;=\int_{B_r} a^2 +(b\cdot y)^2 +|y^T Ay|^2 + 2a(y^T Ay)\,d{y}\\
&amp;=\int_{\mathbb{S}^{d-1}}\int_0^r \left(a^2 + \rho^2(b\cdot \omega)^2+\rho^4 |\omega^T A \omega|^2 +2a\rho^2(\omega^T A \omega)\right) \rho^{d-1}d\rho d\sigma(\omega)\\
&amp;=\int_{\mathbb{S}^{d-1}} \frac{a^2}{d}r^d+\frac{(b\cdot \omega)^2}{d+2} r^{d+2}+\frac{|\omega^T A\omega|^2}{d+4}r^{d+4}+\frac{2a(\omega^T A\omega)}{d+2}r^{d+2} d\sigma(\omega).
\end{aligned} 
\end{equation}
</div>

<p>By Young’s inequality, we have</p>
<div>
$$ |a(\omega^T A\omega)r^{d+2}| \leq \varepsilon a^2 r^d +\frac{1}{4\varepsilon} (\omega^T A\omega)^2r^{d+4}$$
</div>
<p>for any $\varepsilon&gt;0$. This implies that</p>
<div>
\begin{equation}
\begin{aligned}
&amp;\int_{B_r} |a + b\cdot y + y^T A y|^2 \,d{y}\\
&amp;\geq \int_{\mathbb{S}^{d-1}} \left(\frac{1}{d}-\frac{2\varepsilon}{d+2}\right)a^2 r^d +\frac{(b\cdot \omega)^2}{d+2}r^{d+2}\,d{\sigma(\omega)}\\
&amp;\quad+ \int_{\mathbb{S}^{d-1}} \left(\frac{1}{d+4}-\frac{1}{2\varepsilon(d+2)}\right)(\omega^T A\omega)^2 r^{d+4} d\sigma(\omega).
\end{aligned} 
\end{equation}
</div>
<p>We can choose $\varepsilon&gt;0$ so that the numbers in parenthesis become positive numbers since $d(d+4)&lt;(d+2)^2$. This implies that</p>
<div>
\begin{equation}
\begin{aligned}
\fint_{B_r} |a+b\cdot y +y^T A y|^2 \,d{y}&amp;\geq cr^4 \int_{\mathbb{S}^{d-1}} (\omega^T A\omega)^2 \,d{\sigma(\omega)}.
\end{aligned} 
\end{equation}
</div>

<p>On the other hand, note that</p>
<div>
$$ \int_{\mathbb{S}^{d-1}} \omega_i \omega_j \omega_k \omega_l \,d{\sigma(\omega)}=\begin{cases}
1 &amp;\quad \text{if } (i,j)=(k,l)\\
0 &amp;\quad \text{otherwise}.
\end{cases}
$$
</div>

<p>Hence it follows that</p>
<div>
$$
\int_{\mathbb{S}^{d-1}} (\omega^T A\omega)^2 \,d{\sigma(\omega)} =\int_{\mathbb{S}^{d-1}} (\omega_i A_{ij} \omega_j)(\omega_k A_{kl} \omega_l) \,d{\sigma(\omega)}\geq c\sum_{i,j} A_{ij}^2.
$$
</div>
<p>This implies the desired result.</p>]]></content><author><name></name></author><summary type="html"><![CDATA[The following calculation seems quite elementary but it is a bit hard to find it anywhere. However, I need to do it because of new paper. Set $$ \phi(r,X_0)=\sup_{t\in (t_0-r^2,t_0)} \frac{c}{r^2}\left(\frac{1}{|B_r|}\int_{B_r(x_0)} |u(t,x)-q_{X_0,r}(x)|^2 \,d{x}\right)^{1/2} $$ for some $q_{X_0,r}(x)=a_{X_0,r}+ b_{X_0,r} \cdot (x-x_0) + (x-x_0)^T C_{X_0,r}(x-x_0)$.]]></summary></entry><entry><title type="html">Poincare inequality on weighted spaces</title><link href="https://willkwon-math.kr/2023/07/04/Poincare.html" rel="alternate" type="text/html" title="Poincare inequality on weighted spaces" /><published>2023-07-04T10:00:40+00:00</published><updated>2023-07-04T10:00:40+00:00</updated><id>https://willkwon-math.kr/2023/07/04/Poincare</id><content type="html" xml:base="https://willkwon-math.kr/2023/07/04/Poincare.html"><![CDATA[<div>
In this note, we prove Poincar\'e-Sobolev inequality in weighted spaces. Such inequality was first observed by Fabes-Kenig-Serapioni and later simplified by Chiarenza-Frasca.

<blockquote><strong>Theorem.</strong>
Let $1&lt;p&lt;\infty$, $w\in A_p$, and $R&gt;0$. Then there exists a constant $N=N(d,p,[w]_{A_p})&gt;0$ such that 
$$ \left(\frac{1}{w(B_R)} \int_{B_R} |u|^p w dx \right)^{1/p}\leq NR \left(\frac{1}{w(B_R)} \int_{B_R} |\nabla u|^p w dx \right)^{1/p}$$
for all $u\in C_0^\infty(B_R)$. Here $A_p$ denotes the Muckenhoupt $p$-admissible weight. 
</blockquote>
In this note, we follow the proof of Chiarenza-Frasca. The idea follows from an idea of Hedberg. It suffices to show that 
$$ \left(\frac{1}{w(B_R)} \int_{B_R} |I u|^p w dx \right)^{1/p}\leq NR \left(\frac{1}{w(B_R)} \int_{B_R} |u|^p w dx \right)^{1/p},$$
where $I f$ denotes the Riesz potential of order $1$:
$$
  I f(x)=c \int_{\mathbb{R}^d} \frac{f(y)}{|x-y|^{d-1}}dy.
$$
Decompose 
$$   If(x)=I_\varepsilon + II_{\varepsilon},$$
where 
$$
    I_\varepsilon =c\int_{|x-y|&lt;\varepsilon} \frac{1}{|x-y|^{d-1}} f(y)dy 
$$
and
$$
    II_\varepsilon =c\int_{|x-y|\geq \varepsilon} \frac{1}{|x-y|^{d-1}} f(y)dy.
$$

On the one hand, we decompose the integrand into dyadic shell to estimate that
\begin{align}
|I_\varepsilon|&amp;\leq \sum_{j=0}^\infty \int_{\varepsilon 2^{-j-1} \leq |x-y|\leq \varepsilon 2^{-j}} \frac{|f(y)|}{|x-y|^{d-1}}dy\\
&amp;\approx \frac{\varepsilon 2^{-j}}{(\varepsilon 2^{-j})^d}\sum_{j=0}^\infty \int_{|x-y|\leq \varepsilon 2^{-j}} |f(y)| dy\\
&amp;\leq N \varepsilon Mf(x) \sum_{j=0}^\infty 2^{-j}\\
&amp;\leq N \varepsilon Mf(x).
\end{align}

On the other hand, it follows from Holder's inequality that 
\begin{align}
II_\varepsilon&amp;\leq \Vert f \Vert_{L_{p,w}(B_R)} \left(\int_{\{|x-y|&gt;\varepsilon\}\cap B_R} |x-y|^{(1-d)p'} w^{-1/(p-1)}dy\right)^{1/p'}.
\end{align}

By reverse Holder property of $A_p$ weight, there exists $1&lt;q&lt;p$ and $d&gt;p/q$ so that $w\in A_q$. Hence it follows that 
$$
II_\varepsilon (x)\leq c \Vert f \Vert_{L_{p,w}(B_R)}\left(\int_{B_R} w^{-1/(q-1)} dy\right)^{(q-1)/p} \varepsilon^{1-dq/p}.
$$
Hence we get 
$$
If(x)\leq N \varepsilon M f(x) + N \Vert f \Vert_{L_{p,w}(B_R)} \left(\int_{B_R} w^{-1/(q-1)} dy\right)^{(q-1)/p} \varepsilon^{1-dq/p}.
$$
Now we minimize with respect to $\varepsilon$ to get 
$$ If(x)\leq N[Mf(x)]^{1-p/nq} \Vert f \Vert_{L_{p,w}(B_R)}^{p/dq} \left(\int_{B_R} w^{-1/(q-1)} \right)^{(q-1)/dq}.
$$
By taking $L_{p,w}(B_R)$-norm to get 
$$
   \Vert I f \Vert_{L_{pk,w}(B_R)} \leq N \Vert f \Vert_{L_{p,w}(B_R)} \left(\int_{B_R} w^{-1/(q-1)} dy \right)^{(q-1)/dq},
$$
where $k=dq/(dq-p)$. Then we have 
\begin{align}
&amp;\left(\frac{1}{w(B_R)} \int_{B_R} |If|^{pk} w dx \right)^{1/{pk}}\\
&amp; \leq N\left(\frac{1}{w(B_R)} \int_{B_R} |f|^p w dx \right)^{1/p} w(B_R)^{\frac{1}{p}\left(1-\frac{1}{k}\right)} \left(\int_{B_R} w^{-\frac{1}{q-1}} dx \right)^{(q-1)/dq}.
\end{align}

By $A_q$-condition, we have 
\begin{align}
&amp;w(B_R)^{\frac{1}{p}\left(1-\frac{1}{k}\right)} \left(\int_{B_R} w^{-\frac{1}{q-1}} dx \right)^{(q-1)/dq}\\
&amp;=|B_R|^{\frac{1}{dq}}|B_R|^{\frac{q-1}{dq}}\left(\frac{1}{|B_R|} \int_{B_R} w dx \right)^{\frac{1}{dq}} \left( \frac{1}{|B_R|} \int_{B_R} w^{-\frac{1}{q-1}} dx \right)^{\frac{q-1}{dq}}\\
&amp;\leq NR [w]_{A_q}^{1/(dq)}.
\end{align}
This implies that 
\begin{align}
\left(\frac{1}{w(B_R)} \int_{B_R} |If|^{pk} w dx \right)^{1/{pk}}&amp;\leq N R \left(\frac{1}{w(B_R)} \int_{B_R} |f|^{p} w dx \right)^{1/{p}}.
\end{align}
Then the desired result follows from Jensen's inequality.
 

</div>]]></content><author><name></name></author><summary type="html"><![CDATA[In this note, we prove Poincar\'e-Sobolev inequality in weighted spaces. Such inequality was first observed by Fabes-Kenig-Serapioni and later simplified by Chiarenza-Frasca.]]></summary></entry></feed>