Reputation
4,625
Next tag badge:
30/100 score
28/20 answers
Badges
9 36
Newest
 Explainer
Impact
~51k people reached

Jan
22
awarded  Revival
Jan
22
answered Is there a metric space where 2 + 2 = 5?
Jan
22
awarded  Revival
Jan
18
comment Definition of topological space: Is Ω equal to the powerset of X?
@leftaroundabout The indiscrete/trivial topology also is in some sense "behaving as a plain old set". Both are adjoints to the forgetful functor that forgets about topological structure: ncatlab.org/nlab/show/discrete+and+codiscrete+topology
Jan
16
comment Why are sets like $\{x \in \mathbb{Q}|-\pi < x < \pi\}$ both closed and open in $\mathbb{Q}$?
@FemaleTank, There are two different topologies being discussed. One is "balls contain all the real numbers they should", but the other, the one in which the set is both open and closed, is "we only include the rational numbers in any considerations".
Jan
16
revised Is there a relationship between isometry as defined on metric spaces and those on vector spaces?
changed tag from vector space isomorphism to category theory, as that seems to an agreed topic
Jan
16
answered Is there a relationship between isometry as defined on metric spaces and those on vector spaces?
Jan
16
comment Notation of the second derivative - Where does the d go?
@IwillnotexistIdonotexist First, it destroys the nice "multiplication" of factors of the form $\frac{\partial}{\partial x}$ by saying something like "$\partial\partial=\partial^2$ on top, but $(\partial x)(\partial y)=\partial xy$ on bottom". More importantly, IMO, is the fact that, in general: $\frac{\partial}{\partial x}$ and $\frac{\partial}{\partial y}$ don't commute, but $x$ and $y$ do. So to use the notation you proposed would require that $\partial xy$ in a denominator can't be replaced with $\partial yx$, even though in all other real-anaylsis contexts $xy\to yx$ would be fine.
Jan
16
comment Notation of the second derivative - Where does the d go?
@IwillnotexistIdonotexist I don't think I've seen a multivariable calculus book that does that. I've only seen books write things like $\partial x\partial y$ in the denominator, and I believe for good reason.
Jan
14
comment Having $\pi$ fingers and count
Your question is more or less answered at math.stackexchange.com/questions/1465617/…
Jan
13
comment Trouble with Discrete Math proof
Certainly, $A>B>0$ always implies $A>0$. But does that mean it can't also imply $A\le0$?
Jan
13
comment Trouble with Discrete Math proof
The statement given in the problem is true, not false. Justin has written the reason why in a comment in his question.
Jan
13
comment Trouble with Discrete Math proof
Daniel, you may want to reread the whole statement. @Justin, that's not quite the contrapositive.
Jan
13
comment Trouble with Discrete Math proof
Have you tried sketching a graph of $n$ and $n^2+1$?
Jan
12
revised What's between the finite and the infinite?
added infinity tag
Jan
11
comment Definition: Mathematical way to define the “left” and the “right”
@TonyK, it was definitely Feynman. Do a search for the text: Extend your right hand,” you say, to which the alien responds, “What is right
Jan
6
comment Terminology for a game in which Black and White have the same “probability” to win
of course, that's a fine definition of nonpartisan, and applies here. If this were English.SE, I wouldn't have said anything; I just wanted to warn people interested in the mathematical study of these games that that word in particular may lead to confusion.
Jan
6
comment Terminology for a game in which Black and White have the same “probability” to win
Nonpartisan might be confused for the technical terms "impartial" or "not partizan" in combinatorial game theory.
Jan
6
answered Terminology for a game in which Black and White have the same “probability” to win
Jan
3
comment A map from $(0,1)$ to $(0,1)$ such that the image of every open interval in $(0,1)$ is $(0,1)$
This reminds me a lot of Conway's base 13 function.