Hanul Jeon

South Korea

http://hanuljeon95.github.io

I am Hanul Jeon. I am currently (6 May 2020) an MSc student at Seoul National University. Contact me via e-mail or my Twitter account if you want to say something to me. (My e-mail address is available on my website.)

If you find any grammatical errors or suspicious facts from my comments or answers, please let me know.

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Can we prove the existence of $A\cup B$ without the union axiom?

set-theory axioms asked Sep 19, 2013 at 5:35

math.stackexchange.com

15 votes

If polynomial with rational number is injective on rationals then it is injective on reals?

polynomials asked Jul 5, 2013 at 1:11

math.stackexchange.com

12 votes

Is the existence of double complement of a set provable in Intuitionistic ZF?

set-theory lo.logic constructive-mathematics asked Apr 3, 2018 at 11:39

mathoverflow.net

11 votes

How to prove the Milner-Rado Paradox?

set-theory ordinals asked Jul 10, 2013 at 4:57

math.stackexchange.com

10 votes

Set theory determined by $V_\alpha$ for limit ordinals $\alpha>\omega$

set-theory lo.logic asked Jan 17, 2022 at 1:22

mathoverflow.net

9 votes

Can we have a 'universal class' for elementary embeddings $j\colon V\to V$

set-theory lo.logic large-cardinals asked Jan 19 at 4:55

mathoverflow.net

9 votes

The relation between $\Pi_1$-Foundation and $\Sigma_1$-Foundation over Kripke-Platek set theory

set-theory lo.logic asked Mar 25 at 22:44

mathoverflow.net

9 votes

The cardinality of the set of all linear order types over $\omega$ is $2^{\aleph_0}+\aleph_1$ in ZF+AD?

set-theory asked Apr 19, 2014 at 2:22

math.stackexchange.com

9 votes

How much choice follows from the existence of derangement?

set-theory axiom-of-choice asked Apr 29, 2020 at 8:40

math.stackexchange.com

9 votes

Well-foundedness of cardinals and the axiom of choice

set-theory cardinals axiom-of-choice asked Jan 31, 2016 at 11:43

math.stackexchange.com

Top Answers

which is larger number? $\sqrt{7}-\sqrt{6}$ or $\sqrt{6}-\sqrt{5}$

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Convergence of Ratio Test implies Convergence of the Root Test

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The series $\sum_{n=1}^{+\infty}\frac{1}{1^2+2^2+\cdots+n^2}.$

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Does $\bigcap_{n=1}^{+\infty}(-\frac{1}{n},\frac{1}{n}) = \varnothing$?

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Is the function $ f(x,y)=\frac{xy}{x^{2}+y^{2}}$ where $f(0,0)$ is defined to be $0$ continuous?

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Calculating the limit $\lim((n!)^{1/n})$

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An inequality $\,\, (1+1/n)^n<3-1/n \,$using mathematical induction

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Without the Axiom of Choice, does every infinite field contain a countably infinite subfield?

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Does the sequence $1,-1,1,1,-1,1,1,1,-1,1,1,1,1,-1,1,1,1,1,1,-1,\ldots$ have a closed form?

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Every compact metric space is complete

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Prove or disprove that $\int_a^b |f(x)|\ \mathrm{d}x\geq \big | \int_a^b f(x)\ \mathrm{d}x\big| $

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$3x^2 ≡ 9 \pmod{13}$

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In what sense is $\sf ZFC$ "stronger" than Peano arithmetic?

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If $G$ has no proper subgroup, then $G$ is cyclic of prime order

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Translation of "The joy of learning" by Hironaka

mathoverflow.net

Bounded sequence with divergent Cesaro means

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Prove that $[0,1]$ is not a compact subset of $\mathbb{R}$ with the lower limit topology, i.e. open sets are of the form $[a,b)$.

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Prove that $n^2 + n +1$ is not divisible by $5$ for any $n$

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Does there exist any surjective group homomorphism from $(\mathbb R^* , .)$ onto $(\mathbb Q^* , .)$?

math.stackexchange.com

Is axiom of constructibility $V = L$ consistent with Tarski–Grothendieck set theory?

mathoverflow.net

Does $A\times A\cong B\times B$ imply $A\cong B$?

math.stackexchange.com

Prove $\int_0^{\infty } \frac{1}{\sqrt{6 x^3+6 x+9}} \, dx=\int_0^{\infty } \frac{1}{\sqrt{9 x^3+4 x+4}} \, dx$

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Does cancellation property imply invertibility?

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Evaluating $\lim\limits_{n\to \infty}\left\{(1+\frac{1}{n})(1+\frac{2}{n})\dots(1+\frac{n}{n})\right\}^{\frac{1}{n}}$

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Find a subset of $\mathbb{R}^2$ that is path connected but is locally connected at none of its points.

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Show this metric generates the product topology on $X$

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Suppose $(a_n)$ is a sequence such that $a_n=\frac{1!+2!+\cdots+n!}{n!}$. Show that $\lim{a_n}=1$

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Constructing a subset of an uncountable set which is neither countable nor co-countable

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Proving $\mathbb{Q} \times \mathbb{Z_2} \ncong \mathbb{Q}$

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if $(ab)^{3}=e\Rightarrow(ba)^{3}=e$, this is true?

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