whenever I run :   sudo apt-get update   I get this message below:   W: The repository 'cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1) xenial Release' does not have a Release file.  N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.  N: See apt-secure(8) manpage for repository creation and user configuration details.  W: The repository 'ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu xenial Release' does not have a Release file.  N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.  N: See apt-secure(8) manpage for repository creation and user configuration details.  E: Failed to fetch cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)/dists/xenial/main/binary-amd64/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs  E: Failed to fetch cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)/dists/xenial/main/binary-i386/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs  E: Failed to fetch ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found  E: Failed to fetch ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found  E: Some index files failed to download. They have been ignored, or old ones used instead.   I used    sudo nano /etc/apt/sources.list   and comment or remove lines that include cdrom. eg:  deb cdrom:[Ubuntu-Server 16.04 LTS Xenial Xerus - Release amd64 (20160420.3)]/ xenial main restricted&gt;   I was be able to remove it. when I ran sudo apt-get update , got the error message below.  W: The repository 'http://ppa.launchpad.net/ubuntu-on-rails/ppa/ubuntu xenial Release' does not have a Release file.  N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.  N: See apt-secure(8) manpage for repository creation and user configuration details.  E: Failed to fetch http://ppa.launchpad.net/ubuntu-on-rails/ppa/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found  E: Some index files failed to download. They have been ignored, or old ones used instead.   could anyone shed some light on this please ? Thanks a million in advance.
PPA seems to be constantly offline. Whenever I use sudo apt-get update, this error is shown:  W: Failed to fetch http://ppa.launchpad.net/ 404  Not Found   How do I fix these errors?
Worf was seen still wearing the red colours on Star Trek Nemesis. Was he still a strategic operations officer, or did he become tactical officer again despite wearing red colours? When typesetting URLs in LaTeX using the url package, they are set in a mono space font by default. While I just accepted that as a fact for a long time, I am now starting to wonder why?  In Browsers, for example, the URL in the address bar is also not monospace. It does not make the link more readable, in my opinion rather on the contrary. The only explanation I can come up with is that it sets the link apart from the remeaining text. But honestly, even that sometimes looks a bit obstrusive.  So is the reasons really just to set links apart from the text? I have a group $G$ with $p^2$ elements, where $p$ is a prime number. Some (potentially) useful preliminary information I have is that there are exactly $p+1$ subgroups with $p$ elements, and with that I was able to show $G$ has a normal subgroup $N$ with $p$ elements.   My problem is showing that $G$ is abelian, and I would be glad if someone could show me how.   I had two potential approaches in mind and I would prefer if one of these were used (especially the second one).   First: The center $Z(G)$ is a normal subgroup of $G$ so by Langrange's theorem, if $Z(G)$ has anything other than the identity, it's size is either $p$ or $p^2$. If $p^2$ then $Z(G)=G$ and we are done. If $Z(G)=p$ then the quotient group of $G$ factored out by $Z(G)$ has $p$ elements, so it is cylic and I can prove from there that this implies $G$ is abelian. So can we show theres something other than the identity in the center of $G$?  Second: I list out the elements of some other subgroup $H$ with $p$ elements such that the intersection of $H$ and $N$ is only the identity (if any more, due to prime order the intersected elements would generate the entire subgroups). Let $N$ be generated by $a$ and $H$ be generated by $b$. We can show $NK= G$, i.e every element in G can be wrriten like $a^k b^l $. So for this method, we just need to show $ab=ba$ (remember, these are not general elements in the set, but the generators of $N$ and $H$).   Do any of these methods seem viable? I understand one can give very strong theorems using Sylow theorems and related facts, but I am looking for an elementary solution (no Sylow theorems, facts about p-groups, centrailzers) but definitions of centres and normalizers is fine. Auto incrementing field based on groups within feature class? I am needing to auto increment a field based on groups within a feature class. I have 8 plots within a given polygon and I need to assign them an ID from 1-8 for each set of plots within each polygon. The polygon would have its own unique ID number to be used to group the plots.  I assume it would be an alteration of this:  rec=0 def autoIncrement():  global rec  pStart = 1   pInterval = 1   if (rec == 0):    rec = pStart   else:    rec = rec + pInterval   return rec Why is Apache executing .php.html files as PHP? I have an odd problem...I'm using a documentation generator which generates a lot of output like docs/foo.php.html. It's XHTML, and thus contains &lt;?xml...&gt; tags at the beginning of file. The problem is, Apache has somehow decided to run it through the PHP interpreter, even though ".php" appears in the middle of the filename, and not at the end. This, in turn, triggers a PHP error, because it sees "&lt;?" as the command to start executing PHP code, and immediately gets confused by the "xml..." which follows it.  How do I configure Apache to ONLY execute .php files and not .php.html files? The string "php.html" does not appear explicitly anywhere in my Apache config files. There is a line "AddHandler php5-script .php", but I don't see how that would also include ".php.html" files. How delete an application that is bundled with macOS? Backstory:   I am running macOS Sierra and use TextEdit a lot. The problem is that I hate the Versions save schema that causes the universal Save As shortcut of CmdShiftS to instead create a copy of the document. I also hate how Auto-Save makes permanent changes to documents I don't want to modify when I'm tentatively modifying a work-in-progress. Since the introduction of these nuisance features in Lion I have always backed up and then replaced TextEdit.app with the legacy 1.6 version from Snow Leopard.  The problem:  Today when I tried to delete TextEdit.app from my Applications folder using this Terminal command  sudo rm -rf /Applications/TextEdit.app   I got this error  rm: TextEdit.app: Operation not permitted   I was surprised to find that I can't kill it, even with sudo.  How can I actually get rid of an application that is bundled with macOS?  What I've tried so far:  I followed the instructions in , but it didn't work. I also read , which almost accomplishes the same solution by means of disabling Versions and Auto-Save, but then I don't get the benefit of legacy TextEdit's temporary backup saving feature. See the part in the answer stating "This effectively disables the old-style, pre-Lion autosaving completely".   So I think deleting the newer TextEdit v1.12 and replacing it with the legacy v1.6 is still the best option, however I can't get my system to delete it. Any help appreciated. Alien invasion movie, giant robot aliens with long legs capturing people So I saw this movie about 10 years ago, when I was about 5 years old. Since I was really young, my memory of it isn't really that great.   I think it may have been an alien invasion movie, but the only scene I remember is that there were these giant robot-alien things:   I think they had several long legs. They had a big glass dome on top of them They would grab civilians and drop them in their glass dome.   That's all I remember. If you could please help me out, that would be great.   Again, I was about 5 years old when I watched it, so my memory of it isn't that great, but I hope you know what I'm talking about. Thanks so much :) how to change the distance between tick mark and tick label According to the , /opt is for "the installation of add-on application software packages".  /usr/local is "for use by the system administrator when installing software locally".  These use cases seem pretty similar.  Software not included with distributions usually is configured by default to install in either /usr/local or /opt with no particular rhyme or reason as to which they chose.  Is there some difference I'm missing, or do both do the same thing, but exist for historical reasons? I had opened a terminal to install macchanger via sudo apt-get install -y macchanger, and then entered my password. It stated that macchanger was already the newest version, so I typed clear and then ran:  sudo ifconfig eth0 down   which is when this error message appeared:  eth0 ERROR while getting interface flags: no such device   This is a laptop and I am connected via ethernet cable.  How can I resolve this, so that I can run macchanger?    So I used ifconfig -a and I'm looking but seeing no mention of  eth0  The interfaces that are showing top to bottom are:  enp58s0f1 lo tun0 UNSPEC wlp59s0   The only reference to ethernet is the MAC and also txqueuelen   Does this help in figuring what I need to do to get this sorted? Did something change in the behavior of blocking users' votes if they don't have sufficient rep to vote? I've just noticed that if you try to vote without having a privilege to vote, you're greeted with such message:        So, that's interesting. Does it mean that if I gain 125 (or 15, in case I'm upvoting not having 15 reps) rep on that site, my "suggested" vote goes public and until then it would be recorded as it's done with anon feedback?  And until this change, the votes weren't recorded as anonymous, or has the new message saying that it acts as feedback been added just to not upset users? Is there a Term to describe the relationship between two people when they share an Alma Mater?  For example; Neil Armstrong is an alumnus of Purdue University. I am an alumnus of Purdue University. Both Neil and I are alumni of Purdue University, which is to say we share an alma mater. So, I'm looking for a term to describe my relationship to to Neil with out needing to explicitly reference the university. Is co-alumni a real term? Is it appropriate to say that Neil and I are co-alumni? Is there something better? Further, is there a way to specifically describe the relationship between two people from the same graduating class?  Thank You in advance! Can anyone tell me the name of these sentences? Commutator of two normal subgroups with trivial intersections So I tried looking everywhere but I'm really lost with this proof. I need to to show that:  Let $H$, $K$ be normal subgroups of a group $G$, satisfying $H\cap K = \{e\}$. Let $h\in H$, $k \in K$. (a) Prove that the commutator $w = hkh^{-1}k^{−1}$ satisfies $w \in H$ and $w \in K$. Then conclude that $w = e$ (b) Prove that $hk = kh$, for all $h \in H$, $k \in K$. Best way to return multiple values from a function? What is the best practice re: API Version of your Apex Classes? I'm in the process of pushing some updates to some code I originally wrote 12-18 months ago, and the API Version is between 27.0 and 29.0  I know this is to protect the integrity of the test classes you've built (in case they have changed some things) but is there a best practice around either leaving these alone or trying to keep them up-to-date (maybe just once a year instead of at each release)? comma delineation of consecutive endnotes Consecutive footnotes can be separated by commas by invocation of the multiple option of the  package:    \documentclass{article} \usepackage[multiple]{footmisc} \begin{document} Comma delineation of consecutive footnotes fails upon conversion to endnotes% \footnote{First note.}% \footnote{Second note.}.% \end{document}   This comma delineation fails, however, if footnotes are converted to endnotes using the  package:    \documentclass{article} \usepackage{endnotes} \let\footnote=\endnote \usepackage[multiple]{footmisc} \begin{document} Comma delineation of consecutive footnotes fails upon conversion to endnotes% \footnote{First note.}% \footnote{Second note.}.% \theendnotes \end{document}   How can one preserve automated comma delineation of consecutive endnotes? Yesterday I had 3,606 reputation but today I have 3,592.  My profile shows that I lost 6 reputation when a user was removed, but that would put me on 3,600 - 8 reputation has magically disappeared.  Adding up all of my reputation does work out at 3,591 (I'm assuming by default new users have 1 rep, so that would make sense).  Somewhere a reputation change since yesterday isn't being displayed. I don't know what this would be for, but -8 would lead me to believe that someone removed their up-vote on an answer I'd posted which already had a down-vote (could it be from that deleted user?).  I don't know if this is a bug or if there is simply a delay between reputation updating, but I figured it was worth reporting.    Sadly I cannot prove that I had 3,606 reputation yesterday. Why does cout print char arrays differently from other arrays? I'm using C++ to understand how exactly pointers work. I have this piece of code using arrays, which I'm using just to understand how the equivalent works with pointers.  int main() {         int arr[10] = {1,2,3};         char arr2[10] = {'c','i','a','o','\0'};     cout &lt;&lt; arr &lt;&lt; endl;     cout &lt;&lt; arr2 &lt;&lt; endl; }   However when I run this, arr outputs the address of the first element of the array of ints (as expected) but arr2 doesn't output the address of the first element of the array of chars; it actually prints "ciao".  What is it that I'm missing or that I haven't learned yet about this? Last activity name still missing from migrated question