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visits member for 3 years, 5 months
seen 23 hours ago

Apr
14
comment Max and Min using Lagrange Multipliers
$2x$$\mbox{}$ $\ $
Apr
10
answered Book on combinatorial identities
Apr
7
reviewed Leave Open Understanding the Empty set and set theory via proof
Apr
7
comment Understanding the Empty set and set theory via proof
Well, $x-Y$ consists of all elements of $X$ that are not in $Y$. Which of these are also in $Y$?
Apr
7
reviewed Approve suggested edit on Understanding the Empty set and set theory via proof
Apr
7
answered What is bi-infinite matrix?
Apr
6
reviewed Approve suggested edit on Equation with multiplication of a matrix by a column vector
Apr
3
answered how to complete arbitrary basis knowing 2 orthonormal vectors of Rd (d > 2)
Apr
2
comment how to complete arbitrary basis knowing 2 orthonormal vectors of Rd (d > 2)
Theoretically? Then it doesn't matter, completion exists. Practically? Choose random vectors. Anyway: Not suited here, better for math.SE.
Mar
29
comment Why multiply first?
@Frank Not quite. While creating mathematics one should take care that no contradictions are produced. For example one can not just make up some arbitrary distributive law for addition and multiplication. The rule that "multiplication comes first" indeed is a choice as "addition comes first" would also have no weird consequences.
Mar
27
comment Is the Dirac Delta “Function” really a function?
Ah I see. You meant that the individual perception of $\delta$ and $\infty$ may be "exactly the same"… It was not meant as a statement about the mathematical role of either of the two, right?
Mar
27
comment Borel sets and measurability
Isn't there a problem with the null sets? Subsets of null sets should also be null sets and especially measurable but there could be non-measureable subsets of Borel null sets?
Mar
27
comment Is the Dirac Delta “Function” really a function?
Huh? In what exact sense could this be?
Mar
27
reviewed Approve suggested edit on graph-theory tag wiki excerpt
Mar
24
comment Why does $\sqrt[\leftroot{-2}\uproot{2}b]{x^a} = x^{a/b}$ and what does it mean?
"I could prove all sorts of things if you can design rules by myself." Beware! Take good care that your rules do not lead to contradiction. The way one defines $x^{a/b}$ is a sensible and meaningful one. If you come up with another meaningful way, let us know. Also: If you want to generalize $n!$ to non-integer $n$ you have indeed more sensible possibilities (not just the $\Gamma$-function).
Mar
1
awarded  Custodian
Mar
1
reviewed Approve suggested edit on Incorrect calculation? (Statistics homework)
Feb
20
comment Prove that $\sup f(x) \leq \inf g(y)$
That's the wrong round…
Feb
19
answered computation of subdifferential
Feb
3
reviewed Leave Open Prove that for two sets A and B if there is a bijection from A to B, then there is a bijection from pow(A) to pow(B)