Hi I have followed the vimtutor and finished it. After that when I am using vim editor it create backup file as follows  filename.xxx~   does any one know why its create that file and how can I stop that.
I've found that while using Vim on Windows Vim saves the file, a .ext.swp file that's deleted on closing the Vim window and a .ext~ file.   I assume the .ext.swp file is a session backup in case Vim crashes. What's the purpose of the .ext~ file however? Is this a permanent backup file? It's annoying as I'd like to copy all the files I'm working on to my host, without these duplicates. How can I turn this off or, if it's there for a good reason, hide the files?
If I take a sponge and place it in a shallow dish of water (i.e. water level is lower than height of sponge), it absorbs water until the sponge is wet, including a portion of the sponge above the water level. In other words, it seems the sponge pulls some water from the bath up into itself, doing work, and the water gains some gravitational potential energy.  Where does the energy required to do this work come from? My suspicion is that the answer involves physical and/or chemical bonds between the water and the sponge, or possibly the change in the surface area to volume ratio of the water. 'A / One / At least one student entered the room.' Are these the same? (truth-conditionally) I just wonder if the two following sentences are truth-conditionally the same. Sentence 1 essentially means there existed a student who entered the room, and this situation includes two, three or more students entering the room. Hence, I believe these two sentences are truth-conditionally the same. Are they?        A student entered the room.   At least one student entered the room.      How about        One student entered the room      I gather this is different, as sentence 3 only means one student, not more and not fewer?  Any and all insights would be welcome. How can we get rid of misspelled and unused (or "zombie") tags? During the re-tagging of questions, tags sometimes become orphaned from existing questions.  Are these zombie tags ever removed from the ?  What if a tag is misspelled and needs to be removed? How do we get rid of it? SQL Server 2014 - Strange SP behavior during compilation Rearranging display order of attribute table fields using QGIS? My employer didn't send me W-2 for December 2015. In fact, he told me that I wasn't on payroll for the two months(Dec/Jan) I worked for them so I am not sure whether he will be able to generate W-2 for me or not. I am wondering should I call IRS and inform them about the same, and probably they will call the employer? Or should I report my December 2015 earnings as Miscellaneous and report to IRS while filing taxes? Or what other options do I have? I am a non resident alien on F-1 Visa. My employer also has not paid me full salary as promised, which I am discussing with him.  Also, I got paid by check in January month for my December payment, so I am wondering does this apply for 2015 tax filing as I got paid in January 2016? Colors from a computer vs. colors from visible spectrum of sunlight Observation:  So, I know that all computer screens are able to project many different colors by varying how they display the RGB (Red, Green, Blue) pixels.  Question  What's the difference between say, yellow light (575 nm) from sunlight vs. the same yellow light that's displayed on the computer screen? Aren't they different? Is our brains mixing together the RGB lights together and its being interpreted as yellow light or is yellow light the same (575 nm) light that comes from sunlight actually hits our eyes?  Relationship between Fourier Series and light?  1) So I know that in Fourier Series, you have basis functions, sines and cosines that make up any other function depending on the coefficients that are in front of the sines and cosines terms.  2) I know that RGB colors on a screen are the "basis" for all the other colors that a computer screen makes up and the intensity of each of the RGB are like the "coefficients". So, am I making the correct relationship here? I have come across this .  Has anyone tried anything similar or does it work for you? Can you tell if an email customer / user enters is correct &amp; exists? If you activated a free upgrade to Windows 10 or bought and activated   Windows 10 from the Microsoft Store, you have a digital license for   your device. This means you can reinstall the same edition of Windows   10 that your device has a digital license for without entering a   product key. During reinstallation, if you’re asked to enter a product   key, you can skip this step. Windows 10 will automatically activate   online after the installation is complete.   source:   Does MS digital license 'fingerprint' hardware information  during the free upgrade / activation and store it (at Microsoft) , so that the next re-install queries MS for the fingerprint and activates Windows 10?  Thought the disk drive may change, I expect that none of the other fingerprinted hardware will change. Good books on complex numbers I searched on this site but I found posts asking for books on complex analysis which I guess is not what I want.   I want a book on problems concerning with roots of unity, argand plane, exponential form, inequalities etc. Some examples : , , .  I don't think these types of problems are covered in a analysis book but I don't know. I think I want a book on algebra of complex numbers.   Are these topics covered in analysis book ? If not, please suggests some books on this topic. I guess my question is bit vague, sorry for that. :).      As suggested in the comments I would like to have books similar to . I'm trying to remember information about a series of three books I read in the early 1980's (first book could have been published in the 1970's). The book featured a character who was a scientific creation of some sort. It was (initially, I believe) an assassin, and had the ultimate getaway scheme; with effort, it could change its body, becoming about 10 years younger and switching sex. It changed 4 or 5 times in the first book, coming down from a senior citizen to someone in their teens or twenties; in the second and third books, it changed once per book (by the last book, it was a child or a young teenager).  The first book was title something like "The Morph..." where whatever the word was that started with "Morph" was this creature. No recollection of the author's name, or the titles of the other two books.  I think the cover of the first book was predominantly yellow, with black silhouettes representing the character at the four ages seen in the book, and a black title. And/or, the book might have been published by DAW (all their books at the time had yellow spines with black letters). If $A$ commutes with $B$ and $B$ commutes with $C$, then $A$ commutes with $C$ How do I format a backslash as code with backticks in comments? I'm trying to write a single backslash in a comment as code formatted by backtick. Like this:  `\`   but it escapes the backtick and doesn't close the "inline code block".  I've read  but couldn't figure out.  How do I format a single backslash in comment as code? Suppose we have a set  $S=\{a,b\}.$ Obviously, the total number of binary operations on $S$ is the number of all the pairs such that $$*(a,b)=a \, \text{or}  \, b,$$ which gives  $ 2 \cdot 2 \cdot 2 \cdot 2=2^4$ possible ones. Is there a way to find which of these $16$ binary operations are associative without writing all the operation matrices and checking it by hand? Multiple disks vs single disk on virtualized environment We're planning to install a SQL Server on this physical architecture:  A hyper-v cluster based on windows server 2019 A cluster shared volume where all VMs live A full-flash SAN that contains the CSV  I've always read that is a common best practice to have multiple disks for data files, log files, temp db files ect... But that best practice is referred to a bare-bone installation. So, what I'm asking is: what are the actual benefits of doing so on the above described architecture (if any)? Asking days badges A couple of months ago, I suggested a set of badges for . The responses were... mixed. The  can be summarized:  In practice, all this would do is encourage people to ask yet more stupid, worthless questions and we have quite enough of that as it is.  We believe that one of the main things holding back many of our beta sites is that when people have questions they aren't in the habit of asking on the site. Even our flagship site, Stack Overflow, doesn't get many questions from its most knowledgeable users. Perhaps they don't have questions, but far more likely they find answers without needing to ask. Our subtle bias against asking (questions =&gt; clueless) means we lose out on what might be our best source of excellent questions. So we went back to the drawing board and designed a badge set that should not encourage worthless questions:  Asked a well-received question on X separate days, and maintained a positive question record.  In order to award badges, we need to define our terms:  positive question record   (total questions - negative questions - closed - deleted)/total questions &gt;= 0.5  It triple counts a question that is downvoted, closed, and deleted. If you ask one that hits that trifecta, you'll need to ask three better questions to dig yourself out. My own record of asking does not meet the criteria:   (44 - 0 - 12 - 12)/44 = 0.4545...  My  looks a lot better; I had a bunch of questions from the beta period that have been subsequently (and rightfully) deleted. With care, I could bring my record into positive territory with 4 questions. The takeaway is that people can't sweep past indiscretions under the rug by deleting them. And they can recover from a bad start as long as they don't ask more bad questions.  well-received question on X separate days A well-received question is one that's open, not deleted, and has a score &gt; 0. If you ask at least one well-received question in a  and none of your questions that day are deleted, downvoted, or closed, you get one more day of credit toward the badge. Whenever the badge criteria is checked, previous asking days are re-evaluated so that there's an incentive to fix downvoted and/or closed questions. The no-deleted-questions criteria is to prevent people from asking several questions at once and deleting any that aren't upvoted or answered to ask another day. (Though this is a losing strategy in the long run.)   My proposed badge names and levels:  Asked a well-received question on 5 separate days, and maintained a positive question record.  Asked a well-received question on 30 separate days, and maintained a positive question record.  Asked a well-received question on 100 separate days, and maintained a positive question record. In addition, since some outstanding individuals ask on more than 100 days, the gold badge may be awarded multiple times. Over on English, Oishi-sama (now a ) would have a remarkable . Bronze and silver badges are only awarded once. We've decided to hold off on multiple awards for now. See the . Neither the names nor the levels nor even the descriptions are set in stone. Please play around with  to get an idea of how the badge works using our public data. Since the query does not account for deleted questions, it's a bit more generous than the actual badges would be. This version of the badge set should encourage a habit of well-received questions over time and encourage people to fix poorly received questions.  I'd like to express my gratitude to the Parenting community for participating in our . Does a linear operator obeying Leibniz rule imply it is a differential operator? If $q$ is coprime to $a$ then $a\mid nq-1,\,$ so $q$ is invertible mod $a$ I think the following is true:  If $q$ is coprime to $a$ then $a\mid (nq-1)$ for some $n\in\mathbb Z$.  I have started to first reducing $n\in\mathbb Z$ to $n\in\{1,\ldots,a-1\}$ and then considering all the cases $q = ka + j$ for $j=1,2,3,\ldots,a-1$. I stopped at $j=3$ and found that this is kinda messy. Does anyone have an elegant proof for this (maybe using some results from number theory)?  [Note: question has been generalized from prime $q\nmid a$ to $\,q$ coprime to $a$] Proving that a normal, abelian subgroup of G is in the center of G if |G/N| and |Aut(N)| are relatively prime. How to prove that $L=${$a^p$: p is prime} isn't regular? I tried using pumping lemma or finding infinite equivalence classes, but I didn't succeed.  It's clear to me that there is no automata that accepts this language, but I just can't formally prove that this language isn't regular.  How can you prove it?