Today I tried to upgrade my Ubuntu version from 17.04 to 18.04 following , but this didn't work:   $ sudo apt-get update Ign.:1 http://pl.archive.ubuntu.com/ubuntu bonic InRelease Ign.:2 http://pl.archive.ubuntu.com/ubuntu bonic-updates InRelease Ign.:3 http://pl.archive.ubuntu.com/ubuntu bonic-backports InRelease Ign.:4 http://pl.archive.ubuntu.com/ubuntu bonic Release Ign.:5 http://security.ubuntu.com/ubuntu bonic-security InRelease Ign.:6 http://pl.archive.ubuntu.com/ubuntu bonic-updates Release ...   I followed all steps, but sudo apt-get update gives me these errors. How can I revert these changes to first update to Artful and then Bionic?
Recently I have installed an older version of Ubuntu on my old machine. Whenever I try to install any software, I get an error saying it couldn't be found:  $ sudo apt-get install vlc Reading package lists... Done                Building dependency tree        Reading state information... Done     E: Couldn't find package vlc
Where do I place my own .sty or .cls files, to make them available to all my .tex files? I know how to define a package or a class, but how do I make it available (to myself) at all times?  Say I have the package file commonstuff.sty (or myprettyclass.cls), that I want to be able to include in any .tex file I create on my computer. Where do I put it? Do I need to run some installer on it, or is it enough to keep it in a certain folder?  Note: I know I can just place it in the same folder as the .tex file, but that's not what I'm after here. I'm looking for a way to "install" the package centrally on my computer. Technique for finding the nth term I'm a trainee teacher and I need to pass a skills test in maths, but I'm having trouble in this particular area of algebra in finding the nth term of any sequence. I've been given a series of questions to answer one of them is:  Find the nth term of the sequence 3, 8, 15, 24.  I not only need to know the answer but more importantly the technique. This is GCSE level. Why is "cupboard" pronounced with a silent "p"? 9 rows is just way too small by default. Is this a text-editor for ants? I have a list with a people column called AssignedTo.  I'm making a rest call:  .../_api/web/Lists/GetByTitle('listname')/Items?$expand=AssignedTo&amp;$select=*,AssignedTo/Title   Which is successfully returning the name of the person the item was assigned to. I'm trying to get other user information like email or their user id.  Most tutorials online show how to expand ID and Title (Name) and  I found a list of these properties that can be expanded:   ID FirstName LastName Title Department SipAddress   And those all work. But I can't find the email and or the login ID. I've tried $select=AssignedTo/LoginName and several other variations on that, but they all return that the field is not valid. I was hoping $select=AssignedTo/* would expand all the fields, but that doesn't rework either.  Anyone know if the above are the only fields that can be expanded off a people column? JavaScript + Unicode regexes How can I use Unicode-aware regular expressions in JavaScript?  For example, there should be something akin to \w that can match any code-point in Letters or Marks category (not just the ASCII ones), and hopefully have filters like [[P*]] for punctuation, etc. Evaluating $\int_{0}^{\frac{\pi}{2}}\frac{\sqrt{\sin x}}{\sqrt{\sin x}+\sqrt{\cos x}}\, \mathrm{d}x$ What's the difference between terms 'link function' and 'canonical link function'? Also, are there any (theoretical) advantages of using one over the other?  For example, a binary response variable can be modeled using many link functions such as logit, probit, etc. But, logit here is considered the "canonical" link function. show that if $n\geq1$, $(1+{1\over n})^n<(1+{1\over n+1})^{n+1}$ Let $f,g:X\to Y$ be maps of spaces such that $f\simeq g$. Is it true that the mapping cones $\operatorname{cone}(f)$ and $\operatorname{cone}(g)$ are homotopy equivalent?  Can we write down an explicit homotopy equivalence? It ought not to be too hard to get a map $\operatorname{cone}(f)\to \operatorname{cone}(g)$ from the existence of a homotopy $H:X\times I\to Y$, but I haven't been able to find a sensible candidate, despite trying for quite a while. Find the limit if it exists of $S_{n+1} = \frac{1}{2}(S_n +\frac{A}{S_n})$ How to deal with factors with rare levels in cross-validation? Suppose in a regression analysis in R, I have a factor type independent variable with 3 levels in my train dataset. But in the test data set that same factor variable has 5 levels. Therefore I can not predict the response values for test dataset. What should be done in this case? I can't seem to edit and save config files in the root system (eg: /etc/dhcp/dhcpd.config); it just says "permission denied" or the save option is blocked in the text editor.  I'm pretty sure I'm a root user, but how do I make sure? If I am a root user, how do I fix this? Display current layout (language code/country flag) in keyboard indicator Just upgraded from 10.04 to 10.10, and the keyboard indicator applet no longer displays the two-letter country code for the active layout.  This is terrible. Is this the default behaviour? Anyone using two layouts can't tell which language they're in.  I can't seem to find the setting for this, it used to be in the preferences for keyboard layout.  Update 1: In case this wasn't obvious - I have two keyboard layouts - English and Hebrew. I just upgraded form 10.04, where the country code (USA/IL) was displayed, overlaid on the flag.  Now all I get is a vague keyboard icon, and can't find the settings for this.  Update 2: this seems to be a , and is now back in Maverick Recently I have learned how to draw simple stuff with TikZ. I really like it. Now I wonder if it is possible to draw with TikZ on a image. Instead of pasting a image in Illustrator and adding some vectors to point something in the picture I would like to do it using TikZ. Is it possible?   For example, on a picture of a computer (PNG,etc) I would like to draw some arrows and labels saying "Keyboard", "Monitor", etc. Does anyone know what song plays at about ? I was reading a book and this sentence seemed a little odd to me:     At approximately 19.45 hours the two men rose, stretched and yawned. They picked up their gear and stood at the door, ...   What does the first part mean? If it's the exact time, shouldn't it be 19:45? And if it's duration, shouldn't it be "After 19.45 hours"?  (The story here happens at an airbase, if it's of any relevance)    Edit: The book I've quoted is this:   by John Creed.   The author is Irish and the text is set in northern England/Ireland. Why should I avoid multiple inheritance in C++? Is it a good concept to use multiple inheritance or can I do other things instead? How to obtain and use the .bbl file in my tex document for ArXiv submission? When testing the following code:  from osgeo import gdal import json   def read_file(filename):     f = gdal.VSIFOpenL(filename, "rb")     if f is None:         return None     content = gdal.VSIFReadL(1, 10000, f).decode('UTF-8')     gdal.VSIFCloseL(f)     return content   gdal.VectorTranslate('out.json', """{   "type": "FeatureCollection",   "features": [       { "type": "Feature", "geometry": { "type": "Polygon", "coordinates": "coordinates":[[[-188.56933593749997,61.58549218152362],[-173.9794921875,61.58549218152362],[-173.9794921875,66.00015035652659],[-188.56933593749997,66.00015035652659],[-188.56933593749997,61.58549218152362]]] } },   ] }""", format = 'GeoJSON', layerCreationOptions = ['RFC7946=YES', 'WRITE_BBOX=YES'])  got = read_file('/vsimem/out.json') gdal.Unlink('/vsimem/out.json')  print json.loads(got)   from this , the file out.json is empty. The folder is with all permissions for writing allowed. When testing the method gdal.OpenEx, is possible to load an object, but still the method gdal.VectorTranslate returns an empty geojson when trying to pass this new loaded object as a srcDS object. Any hint on solving this issue?