Hi I'm from Vietnam. I'm a grade $10$ students that likes to participate in Math Competition.

Bored by the simplicity of the subject Math at school, I decided to seek hard problems that requires a lot of thinking on here.

I mostly use "we" in my question and answer because using "I" or "you" feels weird for me.

My definition of $\mathbb{N}$ is $\mathbb{N}=\{0\}\cup\mathbb{Z}^+$, however in most answer I just type the full $\{0\}\cup\mathbb{Z}^+$.

I haven't learn anything about Group theory or Category theory.

I usually edit my questions, answers several time right after posting it because lack of information.

If you see me posting an answer and delete it after a few minutes, that's me when I try to post a proper answer while being sleepy, or I got pissed off by the downvotes.

I'm currently studying, or gaming, or eating, or sleeping.

2/24/2025: 1000 reputation.

3/28/2025: First ever gold badge "Fanatic".

4/25/2025: First ever tag badge "integration".

12/24/2025: 10k reputation.

My best work so far.