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Jun
27
answered Non-example for vector space
Jun
27
answered Can ∂x and ∂y in a derivate be seen as ∂ times x or ∂ times y?
Jun
18
comment Why are we defining the norms on certain vector spaces the way they are?
You're right; I've removed that norm (it's a vector norm, but not a matrix norm). Your alternative is the operator-1-norm, therefore it's not a good idea to call it an $\infty$ norm.
Jun
18
revised Why are we defining the norms on certain vector spaces the way they are?
Removed incorrect norm
Jun
18
answered How to generate a random number between 1 and 10 with a six-sided die?
Jun
17
awarded  linear-algebra
Jun
8
comment Open and Closed Sets?
Constant functions are entire functions. But for constant functions and non-empty $S$, $K$ contains a single element, and is thus closed in $\mathbb R$ and discrete in $\mathbb C$, but open neither in $\mathbb R$ nor $\mathbb C$. Moreover, the empty set is an open bounded subset of $\mathbb C$, and for $S=\emptyset$ also $K=\emptyset$, which is both open and closed in $\mathbb R$, and open and discrete in $\mathbb C$. Your answer is correct in the case that $f$ is not constant and $S$ is not empty.
Jun
8
answered Imitating smaller Rubik's cubes with bigger ones.
Jun
8
comment What is the smallest unknown natural number?
Obviously it's the answer to the question "What is the smallest unknown natural number?" The answer to this question is unknown, by definition, and it is known to be a natural number, also by definition. And while in general, for two unknown numbers you cannot say which one is smaller, for this specific problem we know, again by definition, that it is the smallest.
May
18
awarded  Notable Question
May
16
comment Properties of Intersection of Sets
@GregoryGrant: I know what $2^A$ means, basically because I learned it here on math.SE. Before that, I didn't (but I definitely knew what a power set is, and knew the notation $P(A)$ for it).
May
16
comment Properties of Intersection of Sets
@GregoryGrant: Then you would think wrong.
May
16
comment Properties of Intersection of Sets
@GregoryGrant: Not necessarily more people, just another set of people.
May
16
revised Vector Spaces: Redundant Axiom?
added 5 characters in body
May
15
comment What function satisfies $f(x)+f(−x)=f(x^2)$?
Actually the question doesn't specify the domain. So also the function $f:\{-1,1\}\to\{0,1\}$ with $f(-1)=0$ and $f(1)=1$ satisfies the given requirements.
May
15
comment Notation problem in integration: write $dx$ or ${\mathrm{d}}x$?
@ChristianBlatter: What's wrong with $\sin n\pi$? I'm no mathematician, and I don't see anything wrong with it.
May
15
answered What are the “building blocks” of a vector?
May
15
reviewed Reject Interior of closed ball
May
15
revised Riemann's genus???
Marked quote as such
May
14
revised Graphing a parabola
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