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12:56 AM
I was not sure - would fit here?
Q: Family of almost disjoint subsets of $\mathbb{R}_+$ (where non-disjointness is bounded)

xyzzyzLet $\mathbb{R}_+ = [0, \infty)$. I'm looking for a family $\mathcal{U}$ of $2^\mathfrak{c}$ subsets of $\mathbb{R}_+$, such that any member of $\mathcal{U}$ is unbounded in $\mathbb{R}_+$, but the intersection of any two members of $\mathcal{U}$ is bounded. Does such family exists? It would als...

7 hours later…
8:03 AM
Q: What is best tag for "spot the mistake" questions?

Martin SleziakOccasionally we get a question of the form: "Look at this derivation/computation. Clearly, the result is wrong. Where is the mistake?" It is slightly different from typical solution-verification question. Namely here the OP knows that the solution is incorrect, so strictly speaking they do not a...

The above question was inspired by the following question. I added , but I was not sure whether some other tags would be suitable, too. I was considering .
Q: In what way is this limit calculation wrong?

henriqIs something wrong with the calculation below? $$ \begin{align} \lim_{x \to \infty} \frac{4x^2}{x-2} &= \lim_{x \to \infty} \frac{4x}{1-2/x} \\ & = \frac{(\lim_{x \to \infty} 4x)}{(\lim_{x \to \infty} 1-2/x)} \\ & = \frac{(\lim_{x \to \infty} 4x)}{1} \\ & = \lim_{x \to \infty} 4x \\ & = \infty. ...

(BTW I noticed that question from HNQ list.)
15 hours later…
11:01 PM
Q: Tag or communitiy wiki questions on proof techniques

user159517Would it be useful to have tags for common proof-techniques? I thought about this when reading a question like this: how to strictly prove $\sin x<x$ for $0<x<\frac{\pi}{2}$. Lots of inequalities of this type can be proved by writing them as $f(x) \geq 0$ for $x \in [a,b]$ for some real valued s...


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