Unexpected result converting list to array
List.Add seems to be duplicating entries. What's wrong?
Why do people have darker skin in sunnier climates? Checking the way to stop duplicate names - validation rules or triggers It is given in a question that $\vec x+\vec a=(\vec a\cdot \vec x)\vec b$ and it is stated that $\vec a$, $\vec b$ and $\vec x$ are vectors.  It is also stated that $\vec a\cdot \vec b\ne 1$.  The question asks to express $\vec x$ in term $\vec a$ and $\vec b$.  How do you this? I edited my mesh changing the number of vertices after adding shapekeys, and it get totally messed up when the shapekeys are on. Is there a way to solve this problem without remake the shapekeys all again!? Capital letters in "Theorem", "Conjecture" etc This is my first post and as you can probably guess I am a mathematician so I have no clue about grammar. I am writing a mathematical document at the moment and I would appreciate some advice on my usage of capital letters. Can somebody please confirm if the following are correct?  1) "We know by T​heorem 4.6.1 that..."   2) "the following c​onjecture, due to..."  3) In order to prove the "Mckay-Stevens $k$-covering C​onjecture, once needs to show that..."  I'm particularly confused about 3).  Many thanks for any help Graphing y=x^2 and y=x I want to draw the region bounded by y=x^2 and y=x. Any ideas? I was hoping this would be somewhat simple. I've tried used a similar, with \begin{axis}..\end{axis}, but it doesn't like that. Did I not declare a package or something?   Also, if I wanted to show the solid this region creates by rotating it about the x-axis, is there a way to did this in latex? (If you had cal 2, think volume of a solid rotated about ...). Biblatex: Don't show n.d. when no year is given How does faster than light travel violate causality? Let's say I have two planets that are one hundred thousand lightyears away from each other. I and my immortal friend on the other planet want to communicate, with a strong laser and a tachyon communication device.  I record a message on the tachyon communication device and release the message at exactly the same time as I activate the laser, both of which are directed to the other planet which is one hundred thousand lightyears away. Say it is the year 0 for both of us at the time I did this.  If tachyons existed, then the message would arrive to my friend before the photons in the laser. It would arrive, say, a thousand years earlier. From my vantage point, that message will arrive to her at year 99,999; the same would be true for my friend's vantage point. However, she will only see the laser at year 100,000.  So since she got the message at year 99,999, she immediately sends me a reply back going through the same procedure as I did. She records a message and releases it at the same time as the laser. The tachyons will arrive 1,000 years earlier than the laser, so for me, I will receive the message at year 199,998. I will receive the laser, however, at year 199,999.  It seems to me that communication this way does not violate causality. I will still have received the message after I had sent it.   If tachyons truly violated causality, though, I realize it should arrive at year -1 for her, and so she can reply to me at year -2, which would mess me up by year 0 as I will ask her how she knew I was planning on sending her a message before I sent it. I could send her a different message, which she would end up receiving at year -1, and will end up confusing her as she would have received one message asking her out, and the other asking her how did she know I was asking her out. She then decides I am crazy and sends me a message at year -2 that she does not want to date me, and so she will have both turned me down and entertained me before I have even asked her out.  On the other hand, let's go back to year 0 and add a third device to our list: an Alcubierre drive. After I send out the message and the laser, I get impatient and do not feel like waiting 99,999 years, so I get on my Alcubierre drive spaceship and arrive on her planet at the same year 0. My friend is not in her office, so I leave a note to her also immortal secretary saying I dropped by and that she should expect a message for her in year 99,999.  I then get back on my Alcubierre drive and land back on my planet, still on year 0. Meanwhile, the tachyons and photons I sent out are still racing to arrive to her. By year 99,999, she receives the message just as I Alcubierre drive back to her, and I pick her up for dinner.  But the point of my question is, it seems to me that just going faster than light, if that alone was what you had, would not violate causality. It must be something else. I understand time dilation and that things with mass cannot travel at the speed of light, but using the Alcubierre drive, hypothetically speaking, I was still able to outpace the photons while also having mass. It still did not produce causality problems. Alcubierre drives are also valid solutions to GR.  It seems circular to me to say that what makes traveling faster than light violate causality is because it violates causality (if faster than light communication was divorced from causality problems, then the causality problem would cause itself -- thereby violating causality and, hence, we would scrap it and conclude that there is no causality problem after all).  What is it that I am missing? If someone could help me out, that would be excellent. I've been itching to ask my friend out for a few millenia now. :) How to avoid the wrinkle at the poles of the UV sphere? What are best practices for managing SSH keys in a team? I work with small teams (&lt;10) of developers and admins with the following characteristics:   Most members of the team have >1 personal computer, most of which are portable Team members have access to 10-50 servers, usually with sudo   I think this is pretty typical for most startups and small- to mid-size corporate IT groups.  What are the best practices for managing SSH keys in a team like this?  Should you share a single key for the whole team?  Should each person have their own key on a shared account ("ubuntu" on every server)?  Separate accounts?  Should each team member keep a separate key for each of their laptop or desktop computers? Monotone functions and non-vanishing of derivative Why the principal value of complex number argument is taken within $(-\pi,\pi]?$ Why the principal value of complex number argument is taken within $(-\pi,\pi]?$ What is the harm in considering similar other intervals like $[0,2\pi)$ for the purpose? Enable Wireless Monitor mode for traffic sniffing I need to sniff all the wifi traffic that I can capture using wireshark in Ubuntu. My wireless interface is named as eth1 in the interfaces list. When I select that interface in Wireshark and start new sniff, I got following error;    As  thread says, I tried to installed the mentioned driver but I got an error in installation saying that that driver is not supported by my device. After that I tried the second answer in the same thread and run following command to enable monitor mode in my wireless card.  echo 1 &gt; /proc/brcm_monitor0   Then I saw a new Ethernet interface (not a wireless interface ) called prism0 in wireshark interface list. I couldn't start a sniff using that interface using monitor mode because in that interface settings, monitor mode check box has been disabled.  I have installed a broadcom wireless driver in Additional Drivers as follows:    Is there an error listing my Wifi interface as eth1 rather than wlan0 in the interfaces list? How can I start my wireless interface in monitor mode for sniffing?   Thank you. Declare local variables as late as possible or at the nearest curly brace they belong? What is Hawking radiation and how does it cause a black hole to evaporate? My understanding is that  isn't really radiated from a black hole, but rather occurs when a particle anti-particle pair spontaneously pop into existence, and before they can annihilate each other, the antiparticle gets sucked into the black hole while the particle escapes. In this way it appears that matter has escaped the black hole because it has lost some mass and that amount of mass is now zipping away from it.  Is this correct? If so, wouldn't it be equally likely that the particle be trapped in the black hole and the antiparticle go zipping away, appearing as if the black hole is spontaneously growing and emitting antimatter?  How is it that this process can become unbalanced and cause a black hole to eventually emerge from its event horizon and evaporate into cosmic soup over eons? Why doesn't backpropagation work when you initialize the weights the same value? Why doesn't backpropagation work when you initialize all the weight the same value (say 0.5), but works fine when given random numbers?   Shouldn't the algorithm calculate the error and work from there, despite the fact that the weights are initially the same? Most people spend part of each day standing, and if they have normal anatomy their heads are over their heels in this position.  Even sitting or lying down, the head is higher than the heels (if not over the heels).  Yet the phrase "head over heels" is used in ways implying it is an unusual situation.  How did such usage come to be, and why does it persist?  Why is the more obvious "heels over head" not used? Why won't the location of the light affect the direction of the shadows? So I'm new to blender, and I've been working on a project with a tutorial. (some of you might know this)   I was going through quite smoothly until I noticed that no matter where I place my light, the rendered version appears the same. (directly above the objects) I tried different types of lighting, different brightnesses, (light is currently at around 4.000 brightness) nothing works. But if I delete the light, it becomes dark and grainy. (I checked on the side bar, there are no other light sources or objects..)  Even if I put the light source under my objects, the rendered version appears the same.  Am I doing something wrong? Why can't I change the direction of the light?        Uh.. Since I'm not allowed to post more than 2 links, I'll just post extra info here (also replying to @bertmoog)  I tried changing the light types, but they all do nothing (except for Sun, of course, and Hemi, which is interpreted as Sun for some reason) The brightness is set on 4.200, color set to white, shadows enabled, etc. But it still won't do anything. As you can see, nothing appears in the preview.    EDIT: I found that by rotating the sun to point where I want it to, it works almost like normal point lighting (sorta). This pretty much solves my problem, but still, why won't the other lighting modes work? What causes the dimensions of a star increase when its hydrogen fuel is exhausted? Children's fantasy series with a symbol consisting of a circle divided into quarters I read this book series as a kid back in the late 1970s, so it's an old series - and my memories are similarly old, and vague.   I know it's a fantasy series. I think there are 4 books in the series. Or perhaps 7.  There's a central boy character who has to get a collection of magical objects (every fantasy needs a quest!), each of which represents a different magical 'element': wood, stone, fire, etc. I definitely remember there was a wooden object. He lives in our normal world. The whole series takes place "here &amp; now". I have a feeling he's a "chosen" person of some kind... But, the strongest memory I have is of a symbol: a circle which is divided into quarters (a vertical bar and a horizontal bar).  I know it's vague, but does anyone recognise this?