Can anyone tell me the meaning of the words Ign, Hit and Get in the first column of the output from apt-get update?
I had a bunch of errors in the output of sudo apt-get update:  duplicate entries and 404 not found errors.  Figured those out, I hope: I removed PPAs that didn't have any packages associated with them, then I removed out a duplicate entry in /etc/apt/sources.list.  It seems I have royally buggered it up.  Now most of the lines say Ign when I do sudo apt-get update.  How do I go about straightening out what I have screwed up?  I need to get rid of these Igns that are all over the place.  There are about 50% (eyeball guess) Igns!
Prove that $p \in \mathbb{R}[x]$ can be represented as a sum of squares of polynomials from $\mathbb{R}[x]$ I got a UK visa for one month (restricted validity). It expires on November 4. Pakistani citizens are eligible to apply for a Turkish e visa if they have a valid UK visa. I want to visit Istanbul for a couple of days - from October 31 to November 2. Would I be eligible to still apply for an e visa?   My visa is for single entry. It's valid from October 4 to November 4. I am a n00b to physics. What physics I know comes from high school and popular science books.  At school we were taught about atoms and what make up atoms, but we weren't actually told what the particles were!  So sure an atom has electrons orbiting around a nucleus made of protons and neutrons, but what exactly is an ?  And if we don't know, how can we fire them from guns, like they do in experiments ... etc  Any clarification on this would be great. Make links posted by users open in a new window Most of the time when I follow a user's link, I just want to see their site, look it over, then return to answer their question (not leave SO completely and not come back). Could we make the links users post open in a new window please?  EDIT: I originally wanted this implemented because it's what some other sites did, but I now definitely prefer SO's way. If I want to open a new tab, I middle-click/control-click (or whatever); if not, I just click. I'm in control of what happens. Would never want to go back now. Sometimes you see a video of a fan or a propeller spinning very fast, and the apparent rotation is distorted. The fan can appear to be moving in the opposite direction of rotation, or even stationary. This optical illusion is known as the wagon-wheel effect. If I understand correctly, this occurs because the camera framerate is slower than the frequency at which the fan makes one rev, so stroboscopic effects should be expected.   Does the wagon-wheel effect occur only in videos, or can we observe it just with the eye? Sci-fi book about a male entering a competition that he wins and gets recruited by millitary Nonzero $f \in C([0, 1])$ for which $\int_0^1 f(x)x^n dx = 0$ for all $n$ Quick question to anyone who has used this LaTeX template:    Any ideas on how to change the left margin to get more words onto one page? Page number position I am working on a long document in LaTeX with documentclass book. I need the page number to always be in the upper right corner of each page, even if that page is the first page of a chapter (right now on 1st pages of chapters, the page number is bottom-centered, on all other pages it's top-right).  I control the position of the page number with fancyhdr:  \usepackage{fancyhdr} \pagestyle{fancy} \lhead{} \chead{} \rhead{\thepage} \lfoot{} \cfoot{} \rfoot{} \renewcommand{\headrulewidth}{0pt}   Also, I don't know if the problem is related but my chapters do not start from the top of the page. There is a white area, then comes chapter X, then a newline with the chapter line. What I also want is the chapter to start from the top of the page.  The main question here is how I can get the page number to always appear in the upper right corner, I mention the thing with the chapter title position only in case that might be related. Should I use "who" or "that" when referring to an organisation? I generally use the rule of thumb of using who when referring to a person and that when referring to an object. Example:  Jim is someone who makes me smile. I was nearly knocked out by the ball that hit me.  But what about when we're talking about an organisation?  I am forever indebted to the charities who helped me. I am forever indebted to the charities that helped me.  The former seems somewhat warmer, if that makes sense, although the latter feels more correct. What should I use? And how about this:  I'm really happy with the insurance company who helped me with my claim. I can't stand them, they're the insurance company that ripped me off.  To me the former evokes a team of helpful people while the latter evokes a cold heartless corporate entity. Is this just a matter of style and so should go with my instincts, or should I aim for what is 'correct?' Why does chmod 777 -R / leave the system unusable? I'm only granting permission to all to do anything but why does the system crash by giving permissions only? I'm only modifying the permission not changing the files. I read news on the BBC (on its website) this morning. When I was reading the news I noticed the definite article the was missing in a sentence. As per my opinion, the reporter missed the article the. But I also thought that the reporter also had some point as he did not use the article there. So I just wanted to confirm so landed here to get some help on it.     On the website:      It also proclaimed the group's leader, XYZ  (name), as caliph and   "leader for Muslims everywhere".      As per my opinion it should have been:      It also proclaimed the group's leader, XYZ  (name), as the caliph and   "leader for Muslims everywhere".   Source link: MySQL ERROR 1045 (28000): Access denied for user 'bill'@'localhost' (using password: YES) "Friendly" terminal color names in shell scripts? I'm aware of libraries in languages such as Ruby and Javascript to make colorizing your terminal scripts easier by using color names like "red".  But is there something like this for shell scripts in Bash, or Ksh, or whatever? If $x>0$, $\,x^{1/n}$ tends to $1$ as $n\to\infty$ I am looking for a proof possibly using the sandwich theorem and/or Bernoulli's inequality for proving the following statement:  If $x&gt;0$ then $x^{1/n}$ tends to $1$. Is there any way to script Windows 10's "color filter" feature programmatically? What is the "last" data that get's backed up, when running pg_dump on a live server? I'm wondering: If I start doing a pg_dump of a very large database (it would take hours), that is still running actively receiving writes, what is then the last data that goes into the backup? Is it:   The data as-it-was, at the point in time where the pg_dump command was initiated. The last changes that it encountered at some point where it was dumping that individual record. Something else.   Bonus question: If I'm trying to dump a database as part of trying to rescue it from corrupt data, will it then make any difference whether I use the directory format or the custom format? MCMC in a frequentist setting I have been trying to get a sense of the different problems in frequentist settings where MCMC is used. I am familiar that MCMC (or Monte Carlo) is used in fitting GLMMs and in maybe Monte Carlo EM algorithms. Are there more frequentist problems where MCMC is used? (PHP) Is handling a form submission on the same page more/less/equally good as handling on a separate page? RGB and CMYK: Why both? Any of you who have at least little experience with graphic design software, photography or professional printing, must have -almost undoubtedly- have gone through this: 'the struggle' of RGB and CMYK colour spaces.  Now, there are many questions regarding matters of 'which should I choose', 'what is what' and converting problems, but that's not really what I'm after here.  As a graphic designer with only a couple of years of experience, I still have this struggle from time, and find the whole CMYK/RGB choosing/converting/saving situation quite confusing, to say the least. I do know that RGB is meant for digital end purposes, and CMYK is suitable for printing.  I have always been wondering about the neccesity of this whole thing. So, my question is: why are there these two colour profiles, instead of just having one?   Wouldn't it be a lot easier if printers or software could convert any RGB file to a CMYK printing document instead? I'm pretty sure it does already exist, by the way, because printing an RGB file sometimes simply prints the right colours for me. Alas, not always (doesn't seem to be related to the printer of software I print from).    I have gone trough some RGB vs. CMYK-related questions and found this, a.o., (), an answer of user DKuntz2 (thanks DKuntz2):     RGB is a light-based theory. All colors begin with black "darkness",   to which different color "lights" are added to produce visible colors.   RGB "maxes" at white, which is the equivalent of having all "lights"   on at full brightness (red, green, blue).      CMYK is a color-based theory. All colors start with white "paper", to   which different color "inks" are added to produce output colors. CMYK   "maxes" at black, at which point all "inks" are applied at 100% (cyan,   magenta, yellow, black).   Not sure if this is entirely right, though, because some people disagreed with DKuntz2:     I disagree. With RGB you start with black - the absence of light; with   CMYK you start with white paper.   – e100  Although this does clarify the differences fairly well, I still don't see the point of the two colour profiles(/spaces)    Side question: What happens when you work in an RGB document in photoshop, then press ctrl+y? Photoshop says the document is RGB/8/CMYK, but it can't be both. Right?  EDIT:  Big thanks for the answers, the (current) three below are very informative and interesting. I understand the whole thing a bit better, although it's all very complicated and in-depth to me. Especially when I read about terms like colour models, colour profiles, colour spaces, colour spectra and gamut all one after another.  As much as I would like to accept an answer as the desired one, I feel that my question in the core isn't fully answered yet. What I would really like to emphasize is what I asked about earlier: Wouldn't it be a lot easier if printers or software could convert any RGB file to a CMYK printing document instead?. As Alan Gilbertson explained, the reason is - if I understand correctly - basically a 'lost-in-translation' thing that makes the conversion not 100% accurate, and the colours to possibly be a bit distorted.  However, I still don't see how the solution cannot be an automated conversion done by a printer. Should be possible with modern technology; if you can convert RGB to CMYK in Photoshop, why can't a printer do the exact same for you? As was also said in the answers, the slightest differences in colours and colour spaces, can not be seen by the human eye. And that's what it all comes down to: what we want to see. Be it on a screen or on a sheet of paper.  The fact that this question has three very long answers, or even moreso the fact that there are so many questions about these two colour models (I now know the right term, yay) kind of proves that this is way more complicated than it should be.