The point of an NS record is to tell client which name server will know for sure the actual IP address for a domain name. So for instance, the following query tells you that if you want to get an authoritative answer about facebook.com you must ask a.ns.facebook.com:   &gt; dig ns facebook.com                                                                                                                                       19:58:27  ; &lt;&lt;&gt;&gt; DiG 9.9.5-3ubuntu0.8-Ubuntu &lt;&lt;&gt;&gt; ns facebook.com ;; global options: +cmd ;; Got answer: ;; -&gt;&gt;HEADER&lt;&lt;- opcode: QUERY, status: NOERROR, id: 32063 ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0  ;; QUESTION SECTION: ;facebook.com.          IN  NS  ;; ANSWER SECTION: facebook.com.       65000   IN  NS  a.ns.facebook.com. facebook.com.       65000   IN  NS  b.ns.facebook.com.  ;; Query time: 13 msec ;; SERVER: 127.0.1.1#53(127.0.1.1) ;; WHEN: Sun Mar 20 19:58:40 CET 2016 ;; MSG SIZE  rcvd: 65   This seems cool and useful but I'm wondering why the ANSWER section contains the hostname and not IP of the authoritative source? Wouldn't it be easier for the client to get the actual IP address of the authoritative source and not the hostname?  I mean if it gets the hostname it will have to make another query to resolve this hostname into an IP and then ask this new IP about the initial facebook.com domain it was looking for. Isn't this inefficient?   I'd be interested in answer that points me to some paragraphs in some RFC that explains this problem.
This is a  about DNS glue records.   What exactly (but briefly) is a DNS glue record?  Why are they needed and how do they work?
How to recover a deleted NTFS partition with data Were these other people Chronicoms? We know that Enoch is a Chronicom, which is to say a sort of alien temporal observer.   When Enoch and his agents came and kidnapped       Coulson’s team,   for the purpose of sending them where they wanted; were these other agents also Chronicoms? I’m inclined to think they must have been (would Enoch have shared their advanced technology and goals, etc. with mere mortals), but on the other hand only one pod was mentioned. Unknown Column In Where Clause Logarithmic y-axis and restrict y to domain fails I'm trying to plot data with a logarithmic y-axis and restricting the y-data to a specified domain, but compilation fails for a reason I don't understand. This is the code:  \documentclass{standalone} \usepackage{pgfplots} \begin{document}% \begin{tikzpicture} \begin{axis}[ymode=log, restrict y to domain=1:6] \addplot coordinates {(0, 1.1e1) (1, 1.7e3) (2, 0.0e0) (2, 3.4e7) (4, 8.1e5)}; \end{axis} \end{tikzpicture} \end{document}   Running it results in an error message:  ! Missing number, treated as zero. &lt;to be read again&gt;                     i l.6 ..., 1.7e3) (2, 0.0e0) (2, 3.4e7) (4, 8.1e5)};   According to the pgfplots manual for version 1.5.1 (29 December 2011), page 272 (about restrict x/y/z to domain), For logarithmic axes, min and max are logs of the respective values. If I disable either the logarithmic y-axis or the domain-restriction, the code runs successfully and output is as expected (but not as desired).  Software versions:   pdfTeX, Version 3.1415926-2.3-1.40.12 (TeX Live 2011) (format=pdflatex 2012.5.30) pgfplots 2011/12/29 v1.5.1 (git show 1.5.1-4-g53e640f )  tikz 2010/10/13 v2.10 (rcs-revision 1.76).   What's going on? What am I doing wrong? Or is this a bug? Number of non-decreasing functions? Let $A = \{1,2,3,\dots,10\}$ and $B = \{1,2,3,\dots,20\}$. Find the number of non-decreasing functions from $A$ to $B$.  What  I tried: Number of non-decreasing functions = (Total functions) - (Number of decreasing functions) Total functions are $20^{10}$. And I think there are ${20 \choose 10}$ decreasing functions. Since you choose any $10$ codomain numbers and there's just one way for them to be arranged so that the resultant is a decreasing function. However my answer doesn't match. Where am I going wrong? How can I directly compute the non-decreasing functions like without subtracting from total? How much time is too much time playing educational computer games? I recently bought an iPad primarily for my 3-year-old daughter. I put nothing on it but educational apps and children's books. No YouTube, no Internet, no (non-educational) games. I've decided to let her use it as much as she wants, for now, and see how it goes. That was a few weeks ago.  So far she's been using the iPad maybe 2 to 5 hours each day. She still enjoys other activities -- playing outside, playing with dolls and blocks, interacting with friends, being read to, etc. And I think she might be learning a thing or two from the apps. Still, several hours a day seems like a lot. How do I know if it's too much?  I've searched the web, and there's lots of info on limiting TV time and video games, but I can't find any recommendations on limiting use if it's only educational games.  Relevant: App drawer icon gone from Cyanogenmod dock I have a Samsung Galaxy S2, running the latest CM10.1.  I lost the app drawer icon on my Dock; I must have deleted it. The app drawer icon lets you go to the app list, and the widget list.  How do I get the app drawer icon back? The icon looks like a circle with 6 dots inside it. I have a website the seems to load very slowly. When I run a speed test on it I see there seems to be a 6 secound gap before the HTML loads. Images and JS scripts load very fast after that point.  You can see in the pic below the yellow 'wait time' bars:    This seems to be consistant no matter what the HTML content on the page is.  This site is using a CMS (ModX Revo) so HTML is actually stored in an SQL database and brought forth by PHP, but I've never experienced this issue before.  Would anyone know what is causing this and how I could speed it up? A classic exponential inequality: $x^y+y^x>1$ This is a classic problem, but I haven't seen it on the site before.     Suppose $x$ and $y$ are real numbers that both lie in the interval   $(0,1)$. Prove  $$x^y+y^x&gt;1.$$   The following spoiler box contains a hint that indicates the solution I know. Does anyone know a more natural solution?       Use Bernoulli's inequality to show $$x^y\ge \frac{x}{x+y}.$$   Edit: I recently learned the source is the 1996 French math olympiad. Can someone explained, as detailed as possible, the differences between the following types?  List List&lt;Object&gt; List&lt;?&gt;   Let me make this more specific. When would I want to use  // 1  public void CanYouGiveMeAnAnswer(List l) { }  // 2 public void CanYouGiveMeAnAnswer(List&lt;Object&gt; l) { }  // 3 public void CanYouGiveMeAnAnswer(List&lt;?&gt; l) { } How can I remove malicious spyware, malware, adware, viruses, trojans or rootkits from my PC? Why AUC =1 even classifier has misclassified half of the samples? I am using a classifier which returns probabilities. To calculate AUC, I am using pROC R-package. The output probabilities from classifier are:  probs=c(0.9865780, 0.9996340, 0.9516880, 0.9337157, 0.9778576, 0.8140116, 0.8971550, 0.8967585, 0.6322902, 0.7497237)   probs shows probability of being in class '1'. As shown, the classifier has classified all of samples in class '1'.  True label vector is:  truel=c(1, 1, 1, 1, 1, 0, 0, 0, 0, 0)   As shown, classifier has misclassified 5 samples. But, AUC is:  pROC::auc(truel, probs) Area under the curve: 1   Could you please explain to me why it happens? What are the differences between struct and class in C++? This question was .  Now I'd like to learn the differences between a struct and a class in C++. Please discuss the technical differences as well as reasons for choosing one or the other in OO design.  I'll start with an obvious difference:   If you don't specify public: or private:, members of a struct are public by default; members of a class are private by default.   I'm sure there are other differences to be found in the obscure corners of the C++ specification. How to process a multi column text file to get another multi column text file? I have a text file:  a   aa  aaa     b   bb  bbb     c   cc  ccc d   dd  ddd     e   ee  eee     f   ff  fff g   gg  ggg     h   hh  hhh     i   ii  iii j   jj  jjj   How can I process it and get a 2 column file like this:  a   aa aaa b bb  bbb c   cc ccc d dd  ddd e   ee eee f ff  fff g   gg ggg h hh  hhh i   ii iii j jj  jjj   Or a three column file like this:  a   aa  aaa b   bb  bbb c   cc  ccc d   dd  ddd e   ee  eee f   ff  fff g   gg  ggg h   hh  hhh i   ii  iii j   jj  jj   I prefer to get awk solution but other solutions are welcomed too. Can "Wow!" be a sentence? I have a PCB with documentation. In the documentation, there is referred to specific pins of several jumpers and connectors. On the PCB however, there isn't a label or so for which pin has what number. I need to figure out which pin has which number, so that I know the function of each physical pin.  I noticed all connectors have all pins with a rounded tin pad, whilst one pin (either the first or the last when counting from right to left) has a square tin pad:     Is it some kind of convention which number this pin has? After that, how to count the other pins? Drag-and-drop functionality no longer working after upgrade to 19.04 After upgrading from 18.04 to 19.04 (with a necessary upgrade to 18.10 between) on a Lenovo Yoga 11e, I can no longer drag and drop anything (ie, files, windows, etc.) with the touchpad.  I can, however, move things around using the touchscreen.  Whenever I attempt to do so with the mouse, though, sometimes it turns into a hand.  Whether or not it turns into the hand or remains a pointer, the icon will not move anymore.  IOW, as soon as I left-click, the pointer freezes in place until I release the touchpad. How do JavaScript closures work? How can I connect two different DC power sources together? How can I connecting two different DC power sources together? for example 15Vdc(5Amp) with 5Vdc(2Amp). I want to make one DC source (20Vdc,7Amp) by more powerful supplies. I can't create more than 4 partitions