apt-get update not working after vpn issue
What can I do if a repository/PPA does not have a Release file?
Help with Spivak Calculus Ch3 Problem 6a Yet again I find myself stuck on a Spivak question. This time it is simply the question that isn't clear to me. It states:  If $x_1, ..., x_n$ are distinct numbers, find a polynomial function $f_i$, of degree $n-1$ which is 1 at $x_i$ and 0 at $x_j$ for $j\neq i$. Hint: the product of all $(x-x_j)$ for $j\neq i$, is 0 at $x_j$ if $j\neq i$. This product is usually denoted by: $$\prod_{\begin{smallmatrix}{j=1}\\ {j\neq i} \end{smallmatrix}}^n(x-x_j)$$  To be honest I don't know where to begin. I understand how to create a polynomial equation for a given set of results but this is quite strange. I'm not sure exactly what the author is expecting.  The answer book shows:  $$f_i(x)={\prod_{\begin{smallmatrix}{j=1}\\ {j\neq i} \end{smallmatrix}}^n(x-x_j)}/{\prod_{\begin{smallmatrix}{j=1}\\ {j\neq i} \end{smallmatrix}}^n(x_i-x_j)}$$  Which I have expanded out just fine but don't know what to do with. Does a surjective ring homomorphism have to be surjective on the unit groups? How to resume baking fluid simulation? It happens sometimes that after finishing bake (e.g., for fluid simulation) we wish we could continue the simulation for two more seconds :(    How to use the cached bake to continue the simulation?  We played with the settings, but with no success. I am an Indian living in Italy and I am going to the UK for a leisurely family vacation for about 10 days. Please note, this application is not very straight forward. There are four applicants, one applicant is applying from India another two are applying from Singapore and I am applying from Italy. The checklist at the top has the statement  all documents must be in English translated documents must be certified  I got the proof of accommodation from my commune, but it is in Italian. Getting it translated, isn't such a big deal as the commune itself provides multi-lingual certificates. For the rest of the documents, this is an issue. Such as for &quot;Evidence of being in education&quot;, my university provides an online certificate for this purpose which is in Italian. Multiple acquaintances said that they provided their Italian house contract (in Italian) as proof of residency and no requirement came up for translation. Can anyone comment on how strict are they while enforcing the translational requirements of documents in respect to a short term visitor visa? Prove that some topology is not metrizable What good CAD programs are available? Hi Blender coders and artists.  I am updating one of my add-ons for Blender 2.8 and have run into some  issues finding the appropriate way to hide a collection that is added to my scene.  I want to deselect the eyeball on the toolbar with a python command in a script but I don't want to disable the collection in the view-port entirely as it is used as a collection in a particle system.   I just want to deselect the eyeball circled in green below.  Anyone know the python API for this? Is time dilation an illusion? It is said that we can verify time dilation by flying a very accurate clock on a fast jet or spaceship and prove that it registers less time than the clocks on earth. However, the clocks on earth would be moving relative to the clock on the spaceship, and since time always dilates and never goes faster regardless of the direction of relative motion,  the clocks on earth should register less time than the clock on the spaceship.  Is this true? Whenever there is a fast-moving object such as a rocket do all clocks on earth really become slow?  If the rocket with the clock landed after moving at relativistic speed, would its clock and the earth's clock again show the same time since during its travel both appeared slow to each other?  Or is all this just an illusion, ie. the clocks just appear to be slow to each other but in actually run at normal speed, and neither is behind when the rocket actually lands? Test condition in if command Any idea why echo statement is being executed in both scenarios?  Outputs it worked:  #!/bin/bash  rizwan='' if [ -n $rizwan ]; then   echo "it worked" fi   Replace -n with -z, and it outputs it worked when expecting no output:  #!/bin/bash  rizwan='' if [ -z $rizwan ]; then   echo "it worked" fi So, I thought I had a good understanding of this, but just ran a test (in response to a conversation where I disagreed with someone) and found that my understanding is flawed...  In as much detail as possible what exactly happens when I execute a file in my shell? What I mean is, if I type: ./somefile some arguments into my shell and press return (and somefile exists in the cwd, and I have read+execute permissions on somefile) then what happens under the hood?  I thought the answer was:   The shell make a syscall to exec, passing the path to somefile The kernel examines somefile and looks at  of the file to determine if it is a format the processor can handle If the magic number indicates that the file is in a format the processor can execute, then   a new process is created (with an entry in the process table) somefile is read/mapped to memory. A stack is created and execution jumps to the entry point of the code of somefile, with ARGV initialized to an array of the parameters (a char**, ["some","arguments"])  If the magic number is a  then exec() spawns a new process as above, but the executable used is the interpreter referenced by the shebang (e.g. /bin/bash or /bin/perl) and somefile is passed to STDIN If the file doesn't have a valid magic number, then an error like "invalid file (bad magic number): Exec format error" occurs   However someone told me that if the file is plain text, then the shell tries to execute the commands (as if I had typed bash somefile). I didn't believe this, but I just tried it, and it was correct. So I clearly have some misconceptions about what actually happens here, and would like to understand the mechanics.  What exactly happens when I execute a file in my shell? (in as much detail is reasonable...) Loading external GeoJSON file into Leaflet map? I would like to load a geoJSON (polygon) file into my leaflet map. I have seen examples where geoJSON is embedded into the javascript code but I can't find any examples showing how it is done with an external file.   &lt;head&gt;     &lt;meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no"&gt;     &lt;link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.5/leaflet.css" /&gt;     &lt;script src="usStates.geojson" type="text/javascript"&gt;&lt;/script&gt;     &lt;style&gt;         html, body, #map {             height: 100%;         }         body {             padding: 0;             margin: 0;         }     &lt;/style&gt; &lt;/head&gt;  &lt;body&gt;     &lt;div id="map" style="height: 100%"&lt;/div&gt;     &lt;script src="http://d3js.org/d3.v2.min.js?2.9.3"&gt;&lt;/script&gt;     &lt;script src="http://cdn.leafletjs.com/leaflet-0.5/leaflet.js"&gt;&lt;/script&gt;      &lt;script type="text/javascript"&gt;       var map = L.map('map').setView([38.57, -94.71], 4);      L.tileLayer('http://{s}.tile.cloudmade.com/9067860284bc491e92d2342cc51d47d9/998/256/{z}/{x}/{y}.png', {attribution: 'Map data &amp;copy; &lt;a href="http://openstreetmap.org"&gt;OpenStreetMap&lt;/a&gt; Imagery © &lt;a href="http://cloudmade.com"&gt;CloudMade&lt;/a&gt;'}).addTo(map);      var featureStyle = {         "color": "#ff7800",         "weight": 5,          "opacity": 0.2     };      L.geoJson(usStates).addTo(map);      &lt;/script&gt;  &lt;/body&gt; How do function pointers in C work? Feynman diagram for attractive forces How to create a meta-package that automatically installs other packages? I'd like to be able to create a package that doesnt contain any code or programs itself, but instead installs other packages that exist in the repositories onto a computer, sort of how the ubuntu-restricted-extras package does? I have been assigned this problem for homework:     Show that, if $a &lt; b + \epsilon$ for every  $\epsilon \gt 0$, then $a\le b$.   I have tried to go about this using Induction, but I don't know what the base case would be. It is obvious to me in my mind, but I don't know how to put it into mathematical terms on paper. any hints? Why the names Type 1, 2 error? What is the best choice for .NET inter-process communication? Should I use Named Pipes, or .NET Remoting to communicate with a running process on my machine? Asphericity of pseudo circle Let $S$ be de pseudo circle (see for instance ).  How can I compute its higher homotopy groups?  The question came up while trying construct a weak homotopy equivalence $X\to Y$ that does not admit an inverse. Taking $X=S^1$, $Y=S$ and $f$ as in the wikipedia page should work, but I was not able to work out a "simple" way of calculating $\pi_n(S)$ for $n&gt;1$. By "simple" I mean that it should not invoke a generalization of that I am trying to prove. I have several entries in my list of references that include of the order of 40 authors. Is there a way to make bibtex automatically reduce these lists to e.g. the first name + "et al."?  I don't want to edit the BibTeX entries manually and I cannot use biblatex. If at all possible I would also make as little changes as possible to the bibliography style.  There are similar questions, but none of those had a concise answer:       natbib e.g. seems to change only the reference within the text, but not the entry in the bibliography.  EDIT: I am using \bibliographystyle{unsrt} as style definition. How to find Windows 7 File Transfer History?