How to purge previously only removed packages? I have a list of packages on my system, that were installed and removed again, but not purged, i.e. there are still a lot of conffiles etc. laying around.  The output of dpkg --get-selections | grep deinstall lists about 85 different packages which I don't need and want to be purged entirely.  So my short question, which I decided to finally ask after experimenting around has lead to , is:  How do I completely purge previously installed packages that are already removed?  Reinstalling and then purging is not an option, of course.
Can I purge configuration files after I've removed the package? I was doing a package removal with apt-get remove but then realized I should have done a --purge along with it to remove the configuration files.  Can I remove the packages configuration files easily or do I need to reinstall the package and then remove with a --purge?
What is the physical meaning of $\epsilon_0$? I've just been downvoted. How should I react? How to publish a GML file as a Web Feature Service (WFS)? This is, how I download various master branches from GitHub, and I aim to have a prettier script (and maybe more reliable?).  wget -P ~/ https://github.com/user/repository/archive/master.zip unzip ~/master.zip mv ~/*-master ~/dir-name   Can this be shorten to one line somehow, maybe with tar and pipe?  Please address issues of downloading directly to the home directory ~/ and having a certain name for the directory (mv really needed?). How are parameters evaluated for a Plot in Manipulate Pattern Match symbols that begin with same letter? What is the difference between range and xrange functions in Python 2.X? When to use single quotes, double quotes, and backticks in MySQL Adding layers to GeoPackage using PyQGIS How long was Luke Skywalker's training with Yoda? "Your python3 install is corrupted" I want to upgrade from Ubuntu 16.04.5 LTS to 18.04, so ran sudo do-release-upgrade. After downloading and extracting bionic.tar.gz I get:  Can not upgrade   Your python3 install is corrupted. Please fix the '/usr/bin/python3' symlink.   I saw  and so I did sudo ln -sf /usr/bin/python3.6 /usr/bin/python3 thinking that it would be a similar problem. But that didn't work (still same error message).  I have a few python versions:  $ ls /usr/lib | grep python python2.7 python3 python3.5 python3.6  $ update-alternatives --display python3 python3 - auto mode   link best version is /usr/bin/python3.6   link currently points to /usr/bin/python3.6   link python3 is /usr/bin/python3 /usr/bin/python3.5 - priority 1 /usr/bin/python3.6 - priority 2   How do I fix python3? Consider the following sentence:     The labour-intensive and time-intensive part starts tomorrow.   I want to write this without rewriting the word "intensive."  Is this the correct way to do it?     The labour- and time-intensive part starts tomorrow.   Note the hyphen hanging after the word labour. Or should there be no hyphen after labour? Can anyone point me to a reference that talks about this? How do I get the latest GIMP version available? I understand that there is a new version of the GIMP available, although it appears that the only way of doing this is by compiling from source :P  Is there another way of getting it, or if I have to compile can I do that through the terminal or better still; a GUI? How do you update an Excel file (Data Refresh and update formulas) WITHOUT opening the file? I have an Excel file that want to update and save automatically with out having to open it or manually interact with.  Manually, I open the file up and hit data refresh which goes and does a SQL query and then hit F9 for the formulas to update and then I just close/save.    (I then would mail the file out to people using a perl script or use SAS JMP to run some numbers/charts and also mail them out.  Basically I need to script some things which require the XLS file to be updated.) Why don't electromagnetic waves require a medium? As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing electric field is created at point Y and this repeating process is what creates EM waves, so therefore, it requires no medium. Is my understanding correct?  One thing that I'm surprised to know is that light is also called an electromagnetic wave.  Does this include light of any kind, for example: light from a bulb, a tube, and also from the Sun? How do they contain electric and magnetic fields? I am generating a fairly large index of .txt, .tex, and .pdf files. This process has worked for a long time, and the size of the index is not the issue. I have added logic to insert additional links in the index and now am running into:  TeX capacity exceeded, sorry [save size=80000]  Questions:  What are the typical causes of this kind of problem, and any suggestions on how to determine the cause of this. Can the save size be increased?  Of course any solution that just allows me to increase the save size would be preferable if it works, the first question is only important if the size can't be increased or I run into this problem again. Notes:  Generating smaller indices seems to work just fine, only when I attempt to generate the entire index do I run into problems, so coming up with a MWE will be difficult. I believe I have solved a famous open problem. How do I convince people in the field that I am not a crank? Using Integration By Parts results in 0 = 1 Solve the integral $\int_0^\infty x/(x^3+1) dx$ I'm new here!  The problem: integrate from zero to infinity x over the quantity x cubed plus one dx. I checked on wolfram alpha and the answer is that the indefinite integral is this:  $$\int \frac{x}{1+x^3} dx = \frac{1}{6}\left(\log(x^2-x+1)-2 \log(x+1)+2 \sqrt{3} \arctan((2 x-1)/\sqrt{3})\right)+\text{constant}$$  and the definite integral is this:  $$\int_0^\infty \frac{x}{1+x^3} dx = \frac{2 \pi}{3 \sqrt{3}}\approx 1.2092$$  I am trying to figure out all the steps in between. I see that there are logs, which are equivalent to the ln variant that i am more familiar with, which means it was integrating $1/x$ at some point; I also see an inverse tangent in there.  I started with long division to simplify and I got (which could be wrong because I am very tired right now) $x/(x^3+1) = x^2+ 1/(x^3+1)$ which seems to be a step in the right direction. Wolfram Alpha thinks I definitely did that step wrong. The two equations do not evaluate as equal.  Then I cheated and took the wolfram alpha factorization of $(x^3+1) = (x+1)(x^2-x+1)$...I probably should have known that but didn't offhand. Now it is looking like $x^2$ plus the partial fraction decomposition $1/(x^3+1) = A/(x+1)+(Bx+C)/(x^2-x+1)$. Am I heading in the right direction with this? At this point do I just plug in and crunch? Why this :$\sum\limits_{n=1}^\infty\frac1{n\sin n}$ is not harmonic series and is convergent? I'm confused how this series :$$\displaystyle \sum_{n=1}^\infty\frac1{n\sin n}$$ is a convergent series as wolfram show  and it's not harmonic series in the same time .  My question here is:  Why this :$$\displaystyle \sum_{n=1}^\infty\frac1{n\sin n}$$ is not harmonic series and is convergent ?