What is the reason for the /private directory structure located at the root of an OSX system volume?  Why are /etc, /tmp, and /var symlinks to subdirectories of /private?  NOTE While writing my question, I discovered  which seems to address this issue.  I'm going to post my question anyway because it contains the terms that I searched for.  The other question/answer doesn't, prompting me to start writing this question in the first place.
Why is /tmp a symlink to /private/tmp on Mac OS X? In other words, why isn't /tmp just a regular directory, like on Linux or BSD? I understand how it works and I don't mind it, I'm just interested in the (historical?) reasoning behind it.
Does metric signature affect the stress energy tensor? If one were to derive the stress-energy tensor for a metric with $(+,-,-,-)$ signature would it be different from the stress-energy tensor derived from the same metric but with $(-,+,+,+)$ signature? I'm using Jabref to manage my Bibliography.  Sometimes, I put directly:     First Author et al.   when adding the article author's name in Jabref.  When compiling my .tex file, LaTeX doesn't recognize the et. al as more names. It takes it as a name/surname.  This is an example of a Bibliography entry in Jabref.  @ARTICLE{Wolf2003,     author = {Wolf, K.et al.},     title = {Compensation mechanism in tumor cell migration: mesenchymal–amoeboid     transition after blocking of pericellular proteolysis},     journal = {J. Cell Biol.},     year = {2003},     volume = {160},     pages = {267–277},    }   This is a .texMWE with the bib entry mentioned:  \documentclass[11pt]{book}   \usepackage{cite}   \bibliographystyle{unsrt} \begin{document}   Here is the bib entry mentioned\cite{Wolf2003}    \bibliography{bibfile}  \end{document}   Here's the output:   How can I solve this problem? How many of Trelawney's prophecies have come true? Throughout the Harry Potter series, Professor Trelawney makes many different prophecies and predictions. Although most of them are implied to be nonsense, often enough they still get fulfilled. Which ones have come true? Which ones have been proven false? Which ones are still possible?  How many of Trelawney's prophecies have come true?  I'm not asking if Divination in Harry Potter is real, or what it is. I am asking for a finite list of which of Trelawney's prophecies came true, and which ones didn't. Convert integers to written numbers Is there an efficient method of converting an integer into the written numbers, for example:  string Written = IntegerToWritten(21);   would return "Twenty One".  Is there any way of doing this that doesn't involve a massive look-up table? If all motion is relative, how does light have a finite speed? I've often heard that Einstein shattered the notion of absolute motion (i.e. all things move relative to one another) and that he established the speed of light as being absolute. That sounds paradoxical to me; I cannot understand how the two concepts can be reconciled.  Before going further, I'd like to say: 1) Over the years, I've seen many layman's explanations on these topics (including the nice YouTube video by Vsauce, ). I understand everything that's said (or, at least, I think I do). Just nothing I've found seems to address this apparent contradiction. 2) More recently, I've tried to find the answer on my own. That includes searching the posts on this site. Some come close (), but nothing I've been able to find seems address specifically what I'm asking.  Back to the question: Relativity shows us that there is no universal frame of reference by which to judge motion, so object A might be reckoned as moving at 10&nbsp;m/s relative to object B or as stationary relative to object C. This is fine for me. I can grasp that the universe has no intrinsic coordinate system, that we only think that way on Earth because we have the ground to move over.  Then there's the speed of light (in a vacuum). The speed of light is the ultimate "speed limit," it's often said. But if there is no universal frame of reference, how can there be any such speed? The very idea only make sense if there is a universal frame.   If one object is moving (uniformly) at 60%&nbsp;c and another object is also moving at 60%&nbsp;c, but in the exact opposite direct, then from the perspective of either one (if they could still see each other) the other would appear to violate that speed limit. All these spacetime bending consequences used to explain why nothing can move past this speed only seems to enshrine the concept that there is some ultimate speed standard. If there is only relative speed, then the concept of light having a specific speed in the vacuum should be a nonsensical one since it having speed (x m/s) would only make sense when measured against some other body.   Since I was very young, it has always sounded to me like motion is only mostly relative, that until you get close to the speed of light, the effects of an absolute frame of reference are negligible. Perhaps that there is an actual fabric of space which everything moves relative to, which is why there is something to expand between galaxies (faster than light can propagate) in the metric expansion of space. Growing up, I always thought this would just start makes sense with time. Now I'm up to a first year (college) level in physics, I even know basic calculus, yet I'm still hopelessly confused.  EDIT:  Thank you to whoever suggested this may be a duplicate of . It and others are very much related and at least partially answer my question. Unfortunately, explaining that distances become shorter and time becomes slower as a way to stop you from exceeding the speed of light does not explain how that speed is not an absolute.  By my reckoning, if all speed is relative, then no matter how fast you go light should always race away from you at the same apparent speed. I.e. there should be no speed limit. For there to be a speed which you cannot exceed or you would catch up (and make time irrelevant) requires the very concept of some external speed by which light can travel and nothing else can reach - thus my logical paradox continues unabated. Prove that $f$ has a fixed point . Is there any elegant way to show that $\mathbb Q(\sqrt[3]{2}, w)=\mathbb Q(\sqrt[3]{2}+w)$, where $w=e^{i\frac{2\pi}{3}}$.  I was thinking to show that $ 9+9 x+3 x^3+6 x^4+3 x^5+x^6$ is the minimal polynomial of $\sqrt[3]{2}+w$, but checking irreducibility seems a bit tedious. How to really clear the terminal? I can issue the clear command or press Ctrl + L to clear the current Ubuntu terminal, but this just shifts previous output upwards and if you use mouse scroll or PgUP and PgDown keys it's hard to distinguish where the output of previous command ends and output of current command begins.  Is there a way to really clear the terminal so I won't see previous command results? How to set up a wi-fi hotspot with an Ubuntu laptop (access point mode)? I've read , and carefully followed the instructions provided. I am sure the wireless card in my laptop supports going into wireless access point mode. But unfortunately, when I use the following command to start hostapd service it throws an error:   $ sudo service hostapd stop  Starting advanced IEEE 802.11 management hostapd                      [fail]    The instructions mentioned above said this could possibly be because my wireless card does not support the g mode, and provided the wiki of hostapd. But what is g mode? I tried to switch to a, or b mode, but it just didn't work.  Can anyone help with this or recommend a tool like connectify in windows ?  ps. I am using Ubuntu 12.04, 32 bit. I have an ADSL wired network, and I want to share it by setting my laptop into a WiFi hotspot with  my windows phone. Node Package Manager got corrupted in some way, now it cannot be installed Why some dragon claw doors do not open? Why is the relationship between atomic number and density not linear? Sometimes (old) comments break the parser, so it would be nice to view their code to check what was (actually) supposed to be there. Is there any way to view a comment's source just like the source link in a post's revision?  edit Another application for this would be the ability to better quote comments in an answer without having to re-markdown them. I need to process a large file, around 400K lines and 200 M. But sometimes I have to process from bottom up. How can I use iterator (yield return) here? Basically I don't like to load everything in memory. I know it is more efficient to use iterator in .NET. Find Nearby Accounts migration to Google Maps API v3 How to upgrade Git on Ubuntu Hardy? Unit testing void methods? What is the best way to unit test a method that doesn't return anything? Specifically in c#.  What I am really trying to test is a method that takes a log file and parses it for specific strings. The strings are then inserted into a database. Nothing that hasn't been done before but being VERY new to TDD I am wondering if it is possible to test this or is it something that doesn't really get tested. Overall reputation scores are headed nowhere but up.  Pretty soon there will be thousands of mods.  What to do?  Thoughts on possibilities:   Thousands of mods is fine.  Carry on. Adjust the threshold values for high-level SO privileges. Do a straight-up inflation adjustment.  You had x rep, then at the turn of the year we applied the Consumer Rep Index to all scores, now you have (x / inflation) rep. Implement a rep decay mechanism, so that inactivity sheds some of the overall rep that's built up. I have a form with a lot of controls on it.  How can I detect when the mouse leaves the form?  I've tried wiring up a MouseLeave event for every single control and the form, but that does not work because those events fire all the time as the mouse passes over controls.  Is there a way that actually works.? What can you say about $f$ and $g$ in the case that $fg$ is 1) Injective, 2) Surjective - Cohn - Classic Algebra Page 15 Question: Are my proofs below valid?   In both cases we are using: $f:A\to B, g: B\to C$  Notation of your type converted: $(g\circ f)(x)=g(f(x))=xfg$    If $fg$ is injective what can be said about $f$ and $g$?  If $fg$ is injective then $f$ is injective:  Proof:  $(x_1fg = x_2fg \implies x_1=x_2)$  $x_1fg=x_2fg$ is clearly true when $x_1f=x_2f$  Which requires $x_1=x_2$, hence $f$ is injective.  If $f$ were not injective, then $x_1fg\ne x_2fg$  $\blacksquare$    If $fg$ is surjective what can be said about $f$ and $g$?  If $fg$ is surjective then $g$ is surjective:  Proof:  $(\forall c\in C)(\exists a\in A) |( a(fg))=c$  This means for $g$ every element must have had been mapped to. How can this be proved Mathematically?  well $(af)g=c$ is surjective, hence $(af)=(b\in B)$ and $bg=c$  $(\forall c\in g)(\exists b\in B)|(bg=c)$  Hence $g$ is surjective.  $\blacksquare$