Are black and white colours?
Is black a color or absence of color?
Given a hotkey, how can I find which program owns it? Does "corresponding author" carry an implied meaning? After reading the question , I got the impression that (at least in the writers' field) the "corresponding author" flag could carry an implied meaning, such as "did more work than the other authors", or "is a more senior author". Is it the case?  I am in mathematics, a field where we typically sort the authors alphabetically, and I've never given any importance to that role (apart from "this author is willing to answer a couple of extra e-mails, if needed"). Does excessive markup affect SEO? From official :     Due to a head injury, Cyclops is unable to shut off his optic blasts   at will and must therefore wear ruby quartz lenses to block the beams.   From the same page:     Cyclops possesses the mutant ability to project a beam of heatless   ruby-colored concussive force from his eyes, which act as   inter-dimensional apertures between this universe and another.   When his eyes are always blocked by ruby-colored beam of concussive force, how does he see? I've heard that Lubuntu consumes less resources than Ubuntu. Is it because of the fact that Lubuntu uses different desktop environment and window manager?  If so, would it be equivalent to install lubuntu-desktop on top of Ubuntu rather than doing a fresh install? Lebesgue integral uniform convergence Let $f_n, f \colon [a,b] \to \mathbb{R}.$ Show that, if $f_n \to f$ uniformly, then the Lebesgue integrals are equal, i.e. $\int f = \lim \int f_n$.  This is clearly true for continuous functions, but how do I handle the case of non-continuous functions? How to change the monitor's refresh rate? How do I change the monitor's refresh rate in Oneiric?   There is no option to do it in the Displays dialog now. By default it's 60Hz, but I need 75Hz on my monitor.  In previous releases there used to be such an option in the Displays dialog.  Edit - Half baked solution  The best I could do so far was:  xrandr -s 1280x1024 -r 75   This is perfect, but my problem is that it isn't permanent. It defaults back to 60 Hz after logging out and back in.  Perhaps this should go into some script and added to startup? I just don't know how to do that. Is there a word for a comment which makes no sense or adds nothing to the current discussion? I came across this problem and I believe Lagrange's theorem is the key to its solution.  The question is:     Let $p$ be an odd prime. Prove that there is some integer $x$ such that $x^2 \equiv −1 \pmod p$ if and only if $p \equiv 1 \pmod 4$.   I appreciate any help.  Thanks. Superman has been exploited by Poison Ivy in Hush, and he's definitely mad in Injustice. What about Batman? Has Batman ever had to be brought to justice/stopped/killed by his fellow superheroes? (That one time when Superman dreams of Batman snapping Joker's neck doesn't count)  Edit: The Dark Knight Returns doesn't count: Batman wasn't really mad, and he wasn't wrong either. $ac\equiv bc \pmod{\!m}\!\!\iff\!\! a\equiv b \pmod{\!\!\frac{m}{(c,m)}}$ [Euclid's Lemma, congruence form] I came across this theorem:   For all integers a,b,c and m&gt;0, if d = GCD(c,m) then a*c ≡ b*c (mod m) iff a ≡ b (mod m/d).  The =&gt;proof states this:  a*c ≡ b*c (mod m) =&gt; m|(a-b)*c                    =&gt; m/d | (a-b)*c/d                   =&gt; m/d | (a-b)                   =&gt; a ≡ b (mod m/d)   I don't understand how to go from step 2 to step 3. The proof states that this is possible because m/d and c/d are coprime. To me this means GCD(m/d, c/d) = 1 but how does this cancel out the whole term? What is the order when doing $x^{y^z}$ and why? What are 'return' pins? On a VGA connector, there are numerous 'ground' pins. Three of these are Red return, Green return and Blue return; But why does each color component have its own ground pin? How do I unit test code that includes a callout? This is a canonical question and answer developed by the community to help address common questions. If you've been directed here, or your question has been closed as a duplicate, please look through the resources here and use them to shape more specific questions. To browse all canonical questions and answers, including more unit test resources, navigate to the  tag.  How do I unit test code that includes a SOAP or REST-based callout, or indirectly calls code that makes a callout? I'm getting an error saying that callouts are not supported. General Relativity Equivalence Is Einsteins Equivalence theorem in General Relativity correct? It seems to me that it neglects the fact that gravitational acceleration depends upon separation distance squared, thus neglecting the effect of tidal forces.   For example, as I sit on earth, I experience the affect of earth's gravity; Although the acceleration on my head is slightly less than the acceleration acting on my feet. If I make the claim that my frame is equivalent to me being in a space ship traveling at g, doesn't that mean my whole body is accelerating at g uniformly? This is contrary to the previous statement though. Why does this PNG image on twitter look different when clicked? This morning on twitter there was a tweet with the text "click on this picture".  When picture is clicked, it's opened in wider viewer, but looks completely different.  I tried to analyze this picture in ACDSee, and I also tried uploading on Facebook, but it's happening only when embedded on twitter. I don't have much knowledge about graphics so please explain this to me. Why does this PNG image change only when clicked on Twitter?  Screenshots (left = before clicking; right = after clicking):     Here's the original . I have attempted a proof of this, but upon looking at my notes, I feel it might be incorrect: it is noticeably simpler than the one in my notes.  Proposition: any permutation in $S_n$ can be written as a product of disjoint cycles.  Proof (attempt): $s\in S_n$. Let $\langle s\rangle$ act on $X=\{1,\cdots,n\}$. Define $x\sim x'\iff x'\in\text{Orb}(x)$ for $x,x'\in X:$ this is clearly an equivalent relation, hence the orbits partition $X$. Each orbit corresponds a cycle in $s$, so we are done.  Does this hold, or have I missed something vital? Excuse my lack of knowledge and expertise in math,but to me it would came naturally that the cubic root of $-8$ would be $-2$ since $(-2)^3 = -8$.  But when I checked Wolfram Alpha for , real it tells me it doesn't exist.  I came to trust Wolfram Alpha so I thought I'd ask you guys, to explain the sense of that to me. Coming from a programming background, where should I start to learn web design? I'm a web developer mainly working in front end developing. My main fields are HTML5, CSS3 and Flash ActionScript 3.0.  Here in Iran, teamwork means nothing for most of the people, but I think it's the most important aspect of our work, especially in web design.   I have poor skills in graphic design and UI design. I always have to work with graphic designers for my websites. They are usually good and skilled designers. But they are all print designers and unfortunately they know nothing about the web and designing for it.  For example, one of the designers that I work with most of the time is a great designer and he won a couple awards for his logo and poster designs. However, he knows nothing about the web and most of my time is spent explaining to him how things work on the web, i.e. in what size he should work, using pixels instead of centimeters, and so on... After all he is a print designer, not a web designer. They often think everything is static and constant, not in motion.  So the best way to work around this is to improve my skills in graphical designing. I just want to be able to design good layouts, make good color selections, and etc for my websites. I do not want to design illustrations and do heavy graphical works. Just design websites with no Photoshop illustrations like posters and etc.  What do you do for your graphic works, and if you do them yourself, which books or references do you suggest I read? Where should I start? Why would I need a firewall if my server is well configured?