Can I post questions while immediately giving an answer, when I think it is important enough to share?  I guess this is not the original spirit of Stack Exchange, though sometimes I think it would be good to have it saved somewhere. Also for myself in the case I might forget the answer...
I might want to answer my own question because:  I arrived at a solution before there were any other correct answers or I like mine better, can I still answer my own question?  I have a folder with lists of code snippets for things I always forget or get wrong, such as regular expressions for processing XML, common WinForms control idioms, etc. Is it considered poor etiquette for Stack Overflow to ask a question I already know the answer to, and then self answer, just so it gets recorded on the website?   Related:          For more information, see &quot;&quot; in the .
Binary search (bisection) in Python I have 256 colors working just fine in konsole,. I thought I'd give tmux a try because, unlike screen, it seems to support vi mode.  However I find that the colors of my prompt show up and this is most likely because I have a 256 color mode prompt. What do I need to do to get tmux to recognize all 256 colors? I installed kubuntu-desktop just to experiment with its interface.  Then I decided to remove and did the traditional apt-get purge and autoremove but it seems elements of kubuntu are still there. For example interface elements, scrollbars, bootscreen etc are still there.  Is there any method I can completely remove without installing a fresh copy of ubuntu? I'm trying to remember a film I saw years ago (1980's?).  The only part I clearly remember is a man and girl being bricked up alive (in a tower?) and escaping by turning his (magically large) coat or cloak into a rudimentary hang glider.  The film had a medieval sword/sorcery setting. $\delta$ differential notation Various textbooks that I am currently consulting (including Spacecraft Dynamics and Control An Introduction - Anton H.J. De Ruiter | Christopher J. Damaren | James R. Forbes Section 1.4, page 32) use $\delta$, not $d$ or $\partial$ to express an infinitesimal quantity. In the context of the reference text above, the symbol is used as part of a general definition for the derivative of a vector. Specifically, given   $$\mathbf{\vec{r}}=\mathcal{\vec{F^{T}_{1}}}\mathbf{\vec{r_{1}}}$$   where   $$\mathcal{\vec{F^{T}_{1}}}$$   is a vectrix   $$[\mathbf{\vec{x_1}} \phantom{s} \mathbf{\vec{y_1}} \phantom{s} \mathbf{\vec{z_1}}].$$  The time derivative of the vector is defined as   $$\dot{\mathbf{\vec{r}}}\triangleq \lim_{\delta t\to 0}\frac{\delta\mathbf{\vec{r}}}{\delta t}.$$  In this context, what is the difference between $\frac{\delta\mathbf{\vec{r}}}{\delta t}$ and $\frac{d \mathbf{\vec{r}}}{d t}$ ?  Note about thermodynamic use of $\delta$: My understanding is that $\delta$ is used in thermodynamic equations to express path dependence of a scalar quantity such as heat or work. What does it mean in the context of an abstract physical vector? Can I easily travel in Italy by bus/train without any prior reservation? I am planning a trip to Italy this coming January. My plan is to land by plane in Roma and then go to France by train/bus stopping in some Northern Italian cities on the way, enjoying the architecture, the atmosphere, the art and and the food.   I want to do it at my own pace, without heavy scheduling. Ideally, I would just decide which cities to visit, and take a train whenever I feel it. I often do this here in South Korea where I am living, taking advantage of the "standing seats" as it is called here, that is travelling (for a cheap price and no reservation) standing on the romm between two cars. From my experience, it is also doable in Taiwan (at least in some trains).  In France, regional trains usually does not need any reservation, so you can buy a ticket and take the train whenever you want.  Can I expect a similar system in Italy, that is a way to make short travels between close cities without reservation?   Example of "short travel": Pisa - Firenze. Any way to tell apart a CPU defect from a mainboard defect? This is problem #6 from Section 1.2 of Ash's Real Variables With Basic Metric Space Topology.   I am asked to show that it is impossible to list the rational numbers in increasing order.   While I know it is possible to list a finite subset of the rational numbers in increasing order, I was wondering if the reason for the impossibility in this case is because there is no least element of $\mathbb{Q}$?   I mean, it's possible to impose an ordering on $\mathbb{Q}$ (correct me if I'm wrong, but it seems possible to compare any two rationals).  But the set $\mathbb{Q}$ is of course, a subset of itself, and the Well-Ordering Principle says that a set $S$ is Well-Ordered only if any subset of $S$ contains a minimal element. Since $\mathbb{Q}$ does not contain a minimal element, it does not appear that it is a Well-Ordered set.   Is this the correct idea as to why it's impossible? If not, could somebody explain to me what the correct idea is and a strategy for proving it?  Thank you ahead of time. I'm struggling with the following question;     For every graph $G$ such that $K_3 \not\subseteq G$ (i.e. $G$ does not contain a triangle), prove that $\chi(G) \leq 2\sqrt{n} +1$ (where $\chi(G)$ denotes the chromatic number).   Any hints? I really cannot see the connection between the triangle-free nature of $G$ and a chromatic number being bounded above by $O(\sqrt{n})$. Large text files load not working on android Since the last update (v1.0.85), I am getting all the question pages blank on the Android app. For those who are confused with the image, I'm using RtL (Right-to-Left) layout.        If I scroll down (quite a bit) I can see the question. But even then I cannot see the question title, the related comments or answers.         App Version: 1.0.85 Device Manufacturer: LGE Device Model: LG-D620   OS Version: 5.0.2 (152541901f156) The kernel and range of the powers of a self-adjoint operator Portable Ruby on Rails environment I got myself a new 8 gig USB key and I'm looking for a decent solution to have a portable RoR environment to learn on. I did the google on it and found a few possibilities, but I'm curious to hear some real life experiences and opinions. Thanks! What do wizard children do before attending Hogwarts? Most of the wand-carriers that come from a non-Muggle family seem fairly uneducated when it comes to interacting with Muggles.  This implies that they don't go to any type of Muggle school before entering into their education at Hogwarts (or whichever Wizarding school they go to), or else they would at least understand some Muggle culture.  What do children from magical families do before going to Hogwarts if they don't go to a traditional school?  Is there any evidence that they're homeschooled? Difference between 'max distance' and 'radius' in Physics.SphereCastAll Why is logistic regression a linear classifier? Since we are using the logistic function to transform a linear combination of the input into a non-linear output, how can logistic regression be considered a linear classifier?  Linear regression is just like a neural network without the hidden layer, so why are neural networks considered non-linear classifiers and logistic regression is linear? Why has Steve Nash moved to the LA Lakers in sign-and-trade deal? Congratulations to Steve Nash on his move to Lakers !  His contract with the Suns has expired so I don't understand why he moved in a sign-and-trade deal.    Why resign and move in trade? Why didn't the Lakers sign Nash without any trade? Why do some people answer in comments? Why do some people post comments that are actually answers to the question? Wouldn't posting an answer be better? I have Blender 2.79 on my Windows 7 system.    I want to install 2.8, but I'm completing some courses which use 2.79.  If I install 2.8, will it automatically replace 2.79?  Will they interfere with one another?  Thanks. Is $\mathbb{R}$ a subset of $\mathbb{R}^2$? Is it correct to say that $\mathbb{R}$ is a subset of $\mathbb{R}^2$? Or, put more generally, given $n,m\in\mathbb{N}$, $n&lt;m$, is $\mathbb{R}^n$ a subset of $\mathbb{R}^m$?  Also, strictly related to that: what is then the "relationship" between the set $\{(x,0)\in\mathbb{R}^2,x\in\mathbb{R}\}\subset\mathbb{R}^2$ and $\mathbb{R}$? Do they coincide (I would say no)? As vector spaces, do they have the same dimension (I would say yes)?  If you could give me a reference book for this kind of stuff, I would really appreciate it.  Thank you very much in advance.  (Please correct the tags if they are not appropriate)