(Editing a file in the etc repertory ) Cannot edit /etc/sudoers file
How to modify an invalid '/etc/sudoers' file?
No reason for anyone to see pending close votes, except OP (and maybe people who already voted) How to get less spacing in math mode LaTeX commands like this:  Here again, four different simulations are run on networks of size  $C^{G} = 25 \times\ 25 = 625$, $C^{G} = 50 \times\ 50 = 2500$, $C^{G} = 250 \times\ 250 = 62500$, and $C^{G} = 500 \times\ 500 = 250000$...   When compiled generate the following:    The spacing in math mode really irritates me. There's too much white space around the equal sign, and the multiplication sign has more right padding than left padding. Is there any way to reduce this spacing? Submit Buttons on the Left or the Right? We have been puzzling over where to put the submit button, on the left or the right. In researching, we noticed that many sites put buttons on the bottom right in dialogue boxes, and on the bottom left in forms.  It makes sense: in a dialogue box it seems to denote finality, being in the endpoint of the window for left–right readers; in a form, the bottom right could be in a different position relative to the rest of the form if the window is resized.  It seems to be a convention, but I don't see anyone talking about this specific phenomenon in the following questions, nor the articles referenced therein:        So, is this level of button position optimization worth it if it creates an inconsistency in button placement? Is this a good way to go? Fontspec causes long underscores My collaborator added \usepackage[no-math]{fontspec} to a document we're working on. The result is that \_ underscores become v. long: cf. pictures below.   \documentclass{article} \usepackage[no-math]{fontspec} \pagestyle{empty}  \begin{document} \textrm{metric\_space} \end{document}   With fontspec:    Without fontspec:   The underscores are about twice as long with fontspec, and also much thinner. My question is, how do I get back to the original width? (Ideally I would like to preserve the thinness -- it looks much nicer than the original.)  In case someone asks, "why are you using \_?", the short answer is that I need to typeset identifiers involving an underscore. See  for an example in context. I'd be happy with using something other than \textrm, if it looks decent in the context of that example. Would a fast interstellar spaceship benefit from an aerodynamic shape? Some (generous) assumptions:   We have a spaceship that can reach a reasonable fraction of light speed. The ship is able to withstand the high energies of matter impacting at that speed.   Given the amount of matter in inter-stellar space, at high speed, would it encounter enough of it and frequently enough that an aerodynamic shape would significantly reduce its drag (and thus save fuel)? In Harry Potter and the Prisoner of Azkaban, Harry sneaks into The Three Broomsticks and overhears Madam Rosmerta, the Minister for Magic, and several Hogwarts teachers discuss his parents' death and the fact that the Potters were under the protection of the Fidelius Charm. Professor Flitwick explains the charm:     ‘An immensely complex spell,’ he said squeakily, ‘involving the magical concealment of a secret inside a single, living soul. The information is hidden inside the chosen person, or Secret-Keeper, and is henceforth impossible to find – unless, of course, the Secret-Keeper chooses to divulge it. As long as the Secret-Keeper refused to speak, You-Know-Who could search the village where Lily and James were staying for years and never find them, not even if he had his nose pressed against their sitting-room window!’   Prisoner of Azkaban - pages 152-153 - Bloomsbury - chapter 10, The Marauders Map   In Harry Potter and the Deathly Hallows, once Ron returns to Harry and Hermione after his and Harry's fight weeks earlier, he tells Harry and Hermione about the Taboo:     ‘NO!’ roared Ron, causing Harry to jump into the hedge and Hermione (nose buried in a book at the tent entrance) to scowl over at them. ‘Sorry,’ said Ron, wrenching Harry back out of the brambles, ‘but the name’s been jinxed, Harry, that’s how they track people! Using his name breaks protective enchantments, it causes some kind of magical disturbance – it’s how they found us in Tottenham Court Road!’   ‘Because we used his name?’   ‘Exactly! You’ve got to give them credit, it makes sense. It was only people who were serious about standing up to him, like Dumbledore, who ever dared use it. Now they’ve put a Taboo on it, anyone who says it is trackable – quick and easy way to find Order members! They nearly got Kingsley –’   Deathly Hallows - page 316 - Bloomsbury - chapter 20, Xenophilius Lovegood   So in hindsight the trio understands that it was the Taboo that caused the Death Eaters to find them at Tottenham Court Road, and then later, of course, they're caught by Snatchers because Harry says "Voldemort" out loud. However, the trio says "Voldemort" numerous times while they're staying at Grimmauld Place and Death Eaters appear and stake the place out (granted, it could be that the Death Eaters simply knew that Harry had inherited Grimmauld Place from Sirius after the Ministry examined Sirius's will). They cannot get inside the house, though. I'm completely unclear as to the status of Grimmauld Place and the Fidelius Charm -- the house was under the charm, but the Secret Keeper (Dumbledore) had died. Nevertheless, like eleventy-one people were privy to the secret by the time of Dumbledore's death, and I have never found a satisfactory answer (to me) to exactly how the Fidelius Charm works.   Would Voldemort's Taboo spell be able to trump the Fidelius Charm?  &#9733; I'm looking for a canon-based answer (Harry Potter novels, the three supplemental books, JKR interviews, and Pottermore) and do not prefer an answer from the HP Wikia or the Wikipedia. (Originally  by AJAY.)  What is the geometric, physical, or other meaning of the third derivative of a function at a point?  If you have interesting things to say about the meaning of the first and second derivatives, please do so. How do I delete multiple rows in Entity Framework (without foreach) What is used in the 12.10 full disk encryption? It is an usual practice that any quantum field theory starts with a suitable Lagrangian density. It has been proved enormously successful. I understand, it automatically ensures valuable symmetries of physics to be preserved. But nevertheless the question about the generality of this approach keeps coming to my mind. My question is how one can be sure that this approach has to be always right and fruitful. Isn't it possible, at least from the mathematical point of view that a future theory of physics does not subscribe to this approach? Let us view our deleted comments If moderators can view , can we see comments we've deleted? We can see our deleted answers, but why not our deleted comments? Experimental observation of matter/antimatter in the universe Why do we use the base form of verbs instead of the past form in past tense questions? Infinite Series: Fibonacci/ $2^n$ I presented the following problem to some of my students recently (from Senior Mathematical Challenge- edited by Gardiner)  In the Fibonacci sequence $1, 1, 2, 3, 5, 8, 13, 21, 34, 55,\ldots$ each term after the first two is the sum of the two previous terms. What is the sum to infinity of the series: $$\frac{1}{2} + \frac{1}{4}+ \frac{2}{8} + \frac{3}{16} + \frac{5}{32} +\frac{8}{64} + \frac{13}{128} +\frac{21}{256} +\frac{34}{512}+ \frac{55}{1024} + \cdots$$  Now, I solved this using an infinite geometric matrix series (incorporating the matrix version of the relation $a_n= \frac{a_{n-1}}{2}+ \frac{a_{n-2}}{4}$), and my students, after much hinting on my part, googled the necessary string to stumble across Binet's formula (which allows one to split the series into two simple, if rather messy, geometrics). Both of these are good methods, but neither really seems plausible for a challenge set for 15-18 year olds under exam conditions. So how is one supposed to do it? I have a method that I would like to call.  However, I'm looking for a clean, simple way to kill it or force it to return if it is taking too long to execute.  I'm using Java.  to illustrate:  logger.info("sequentially executing all batches..."); for (TestExecutor executor : builder.getExecutors()) { logger.info("executing batch..."); executor.execute(); }   I figure the TestExecutor class should implement Callable and continue in that direction.  But all i want to be able to do is stop executor.execute() if it's taking too long.  Suggestions...?  EDIT  Many of the suggestions received assume that the method being executed that takes a long time contains some kind of loop and that a variable could periodically be checked. However, this is not the case.  So something that won't necessarily be clean and that will just stop the execution whereever it is is acceptable. Why can't light escape from a classical black hole? How to run/use popcorn-time? I got popcorn time installed using this link:    But I have no clue how to use or run Popcorn time.  Do I open my torrent client and download a movie and then it gets going? or do I have to open it? If I have to open it, how do I do that, I opened the dash and tried clicking on it but nothing happened. Please help me!! :D Conditional expectation on more than one sigma-algebra The number of different ways to choose $k$ out of $n$ unique items The number of different ways to choose $k$ out of $n$ unique items:   Without repetition and without order-significance: $\binom{n}{k}=\frac{n!}{k!(n-k)!}$ Without repetition and with order-significance: $\binom{n}{k}\times k!=\frac{n!}{(n-k)!}$ With repetition and with order-significance: $n^k$ With repetition and without order-significance: $?$   Thank you! Prove that $\binom{m+n}{m}=\sum\limits_{i=0}^m \binom{m}{i}\binom{n}{i}$ I need to proof this following equality :  $$\binom{m+n}{m}=\sum_{i=0}^m \left(\binom{m}{i}\binom{n}{i}\right)$$  This is what I did combinatoric proof:  Left : subset with $m$ members from $m+n$  Right : $\binom{m}{i} \rightarrow$ The number of subsets in set $m$ could also be written as $2^m$ AND $\binom{n}{i} \rightarrow$ the number of subsets with $m$ members from set $n$  In case $ n \leq m \implies \binom{n}{i}=2^n$  So this is what I came up with I still can't see why those expression are equal.  Any ideas? Thanks.