How to reference list elements when originally initialized like [None] * N?
List of lists changes reflected across sublists unexpectedly
Find the limit if it exists of $S_{n+1} = \frac{1}{2}(S_n +\frac{A}{S_n})$ Determining if a file is a hard link or symbolic link? I'm creating a shell script that would take a filename/path to a file and determine if the file is a symbolic link or a hard link.   The only thing is, I don't know how to see if they are a hard link. I created 2 files, one a hard link and one a symbolic link, to use as a test file. But how would I determine if a file is a hard link or symbolic within a shell script?   Also, how would I find the destination partition of a symbolic link? So let's say I have a file that links to a different partition, how would I find the path to that original file? How do I enable the "Universe" repository? How do I get to the Universe Repository in supported versions of Ubuntu? When $f(x+1)-f(x)=f'(x)$, what are the solutions for $f(x)$? The question is:     When $f(x+1)-f(x)=f'(x)$, what are the solutions for $f(x)$?   The most obvious solution is a linear function of the form $f(x)=ax+b$. Is this the only solution?  Edit  I should add that $f:\mathbb R\to\mathbb R$ to the question. What would be an appropriate opposite of "exceed"? What is the difference between "used space", "size" and "size on disk"? There is only one partition for both system files and personal data, which is C:. The other two partitions are for boot and for recovery.  Now I have two different reports on the size of C: on my Windows 7:   by clicking the property of C:, it shows 59.4 GB for "used space"; by selecting all contents (I have setup to view all hidden files and directories) under C: and viewing their property, it shows 46.9 GB for "size" and 47.6 GB for "size on disk".   Here are my questions:   I was wondering why the two reports are not the same, and where the difference comes? in the second way, why "size" and "size on disk" are different? What do they mean actually? What is the difference between them and "used space" in the first way?   Thanks in advance! What do "." and ".." mean when in a folder? when I used ls -a to view hidden files in folder there were 2 hidden files created by default what is the significance of this two files . and ..?  ls -a   Produces  .  .. What is $i^i$ and $(i^i)^i$ What is $i^i$ and $(i^i)^i$. I fond some answers  but is there a clearer explanation of this? Maybe something help me to understand. So I know the basic gist is that fusion power's main issue is sustaining the fusion. I also know that there are two methods. The Torus method and the laser method. The torus magnetically contains plasma and heats it with radiation and accelerates the plasma around to make strong enough collisions that protons fuse. The laser method uses 192 lasers and focuses it on tiny frozen hydrogen pellets and aims to initiate fusion each time pellets are dropped.  The though struck me when we could sorta combine the two designs together. The torus doesn't have to worry about making fusion happen at a specific location but it has issues in that the plasma is unevenly heated and leaks. On the other hand, the laser design is extremely complicated in the level of precision needed and would have to repeat this for every pellet. This lead me to think to make something precise and contained at the same time.  I see that particle colliders are able to direct two beams of protons and have them collide at a specific spot with a very precise energy. Couldn't we tune the energy of the two beams of protons to the energy required for them to fuse? We have the ability to smash them into bits, surely we have the ability to have them fuse. (I'm thinking about the type of collider that circles two beams in opposite directions)  It would be at much lower energies than normal colliders and would be very precise and it would be possible to fuse at a specific location that has greater leeway because for protons that missed collision, they'd just circle around again! Thus protons would efficiently be used and very little would be wasted. There wouldn't be problems of plasma leakage because we are focusing them in a thin tight beam.   It seems that this idea has girth, or I feel this way at least, can someone back me up by offering some calculations on how to calculate the efficiency? How would I go about calculating the two circling beams of protons and at what specific velocity would be needed? etc. Is there going to be a process around hellbanning? Given , I must say I think the idea (making that user's content visible to only them) is a good one.  However, the people in whose hands that power will be placed terrify me.  Jeff is saying that he doesn't like that bans can degenerate into meta-discussions about the fairness of banning, and in that respect I agree with him. But the meta-discussions do accomplish one thing -- they get more than one person to look at the ban and weigh in on what they think.  This isn't that I don't trust moderators (or, indeed, diamond moderators), but I don't trust any one single human being with an irrevocable and complete banhammer, where there's no potential to dispute things. (And if the user doesn't know they're banned, there's no potential for dispute)  Basically, I'd sleep a lot more soundly at night knowing that if one of these "enhanced bans" are put into place, that at least two people have looked at the "problem child", and only after more than one person has signed off on such a ban, does that go into effect. I don't care exactly what that process is, but I don't want to have to worry about pissing off a moderator and getting banned as a result.  We all get pissed off here -- it's part of any community. But "the nuclear option(s)" need(s) to be decided upon by someone with a cool head, not someone who's pissed off. Convergence of Ratio Test implies Convergence of the Root Test Is there a quick way to get the control that's under the mouse? I need to find the control under the mouse, within an event of another control.  I could start with GetTopLevel and iterate down using GetChildAtPoint, but is there a quicker way? How to draw good arrows explaining parts of equation? Given Newton's third law, why are things capable of moving? Given Newton's third law, why is there motion at all? Should not all forces even themselves out, so nothing moves at all? When I push a table using my finger, the table applies the same force onto my finger like my finger does on the table just with an opposing direction, nothing happens except that I feel the opposing force. But why can I push a box on a table by applying force ($F=ma$) on one side, obviously outbalancing the force the box has on my finger and at the same time outbalancing the friction the box has on the table? I obviously have the greater mass and acceleration as for example the matchbox on the table and thusly I can move it, but shouldn't the third law prevent that from even happening? Shouldn't the matchbox just accommodate to said force and applying the same force to me in opposing direction? What techniques have been used to repeat geometry or other detail to the infinite horizon? Lost access to sudo sudo: unable to resolve host   I think I need to edit the /etc/hosts file to make an entry for 127.0.1.1 PC name.  But how can I do that if I can't access sudo? It seems to have gone since I updated to 13.10.  I have tried nano, which still doesn't work. I've tried to setup an autologin, but that isn't possible, because my home is encrypted. What are the reasons for this?  PS. Here I have described my problem: . I just reinstalled my Ubuntu system with 11.10, but ran into a problem when I tried to install Gimp 2.7.  I always get unmet dependencies (it's german, so I can't tell you the exact english translation):     Needs gimp-data (&lt;= 2.6.11-z) but 2.7.3-2011082002~oo should be installed   I already read the follow post, but the answers didn't really help me.  When I type in     sudo apt-get install gimp=2.6   it just says that there is no version 2.6 found. I get the same with 2.7.  I really need Gimp. But installing Gimp 2.6 isn't possible as well.  When I remove the repos for 2.7, I still get the same error. New navigation doesn't appear to alert of question changes when watching a tag I am watching the  tag on Stack Overflow. My filter looks like this:    I do not receive notification of new questions. Previously I'd get notifications like this:    This notification does work when watching the  page of Meta.   Are notifications only active for a certain set of filter options? If so, what are they? If not, can we get them back when watching pages other than the main page? When ever I need to kill a background process I do ps -e | grep &lt;process_name&gt;  Which prints something like this 1766 ? 00:00:13 conky , Then I use the process ID to kill it like so kill 1766 .   Is there any way I can simplify this ? Make it quicker ? reduce the amount of typing ?