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How can I prove  from first principles that $0!$ is equal to $1$? Trying to keep track of the updates to all the great, user-developed add-ons is fairly frustrating (at least for me). Is there currently a centralized resource where all these amazing add-ons are kept and updated in one location?  If there isn't such a resource, would it be possible to have blender query the collection of installed add-ins and then iterate through on-line references looking at version #'s for add-ins?  Since, as far as I know, it hasn't been done...I have to ask if there are any major flaws in the concept. Of course, in my dream scenario, there would be a "voting" front-end that would allow users to see what the most popular and useful add-ons are and where you don't have to read pages (and pages) of threads. Run a command without making me wait Extract date from a variable in a different format Let me explain you the problem   $ date +%c -d "$d" Tue 31 Dec 2013 01:13:06 PM CET $ date +'Today is %F' -d "$d" Today is 2013-12-31   This solution corresponds to current date.  But I have one variable which stores date other than current date  $Prev_date="Wed Dec 25 06:35:02 EST 2013"    I am looking for solution to read this date as 2013-12-25 and store it in a variable.  I have tried this:  a=`date --date=$Prev_date '+%y/%m/d'` echo $a   It's giving this error:  date: illegal option -- date=Wed usage: date [-u] mmddHHMM[[cc]yy][.SS] date [-u] [+format] date -a [-]sss[.fff] What is an uninterruptible process? Sometimes whenever I write a program in Linux and it crashes due to a bug of some sort, it will become an uninterruptible process and continue running forever until I restart my computer (even if I log out).  My questions are:   What causes a process to become uninterruptible? How do I stop that from happening? This is probably a dumb question, but is there any way to interrupt it without restarting my computer? Infinite group with only two conjugacy classes Strange problem with BibTeX sorting How to access a usb flash drive from the terminal? I only have access to the command line. I need to backup my data (on the user folder) to a pen (USB DOK).    How can I mount a flash drive manually? What should be the copy command? Is Gauss's law wrong, or is it possible that $\int_s{\vec E} \cdot d\vec{s}=0$ does not imply $\vec E = 0$? This is a question from David J Griffith's Introduction to Electrodynamics.      A specified charge density $\sigma(\theta)=k\cos(\theta) $ is glued over the surface of a spherical shell of radius $R$. Find the resulting potential inside and outside the sphere.   The question was solved using legendre polynomials and the final answer for potential inside the sphere was : $V(r,\theta) = \frac{kr}{3\epsilon_0}cos\theta$  This final answer is confusing because The Electric field inside the sphere is coming out to be dependent on $r$ and $\theta$ whereas electric field inside a shell, no matter what the charge distribution is outside, is $zero$ from gauss's law.      my doubts:         why is the electric field inside non zero?    Can gauss's law explain this, or does it fail here?      Since solving using ordinary surface integral gave me the same result and since the. divergence inside the shell is $zero$, I concluded that legendre polynomials and gauss's law in differential form are correct. So the problem should be with the integral form of gauss's law : $\int_s{\vec E}.d\vec{s} = \frac{q}{\epsilon_0}$  The answer I got for this doubt is that  "since the charges are glued to the surface, and not evenly distributed, electric field inside need not be zero. "     This is not convincing because proof of gauss's law does not expect the charges to be free to move. presence of an exrernal force that would hold the charges in place does not change the theorem. That is    Say only a single charge $q_i$ is present outside      then $\int_s{\vec E_i}.d\vec{s} = \frac{q_{inside}}{\epsilon_0}=0$      Now if there are more charges, following any distribution, net electric field $\vec E = \vec E_1 + \vec E_2+\vec E_3+...$       So the net flux,       $\int_s{\vec E}.d\vec{s} = \int_s{\vec E_1}.d\vec{s}+\int_s{\vec E_2}.d\vec{s}+\int_s{\vec E_3}.d\vec{s}+. . .=0$   Or is it possible that $\int_s{\vec E}.d\vec{s}=0$ does not imply $\vec E = 0$? It seems the .NET Regex.Replace method automatically replaces all matching occurrences.  I could provide a MatchEvaluator delegate that returns the matched string after the first replacement, rendering no change, but that sounds very inefficient to me.  What is the most efficient way to stop after the first replacement? What does $(command) & do? I saw the following syntax in a bash script:   &gt;$(command) &amp;   I know that the ampersand &amp; at the end makes a command run in the background, but I have never seen it in combination with the dollar sign plus the brackets around the command.  What does it do? Is there a way to give a profile a different default list view then "Recently Viewed" in Lightning? FaceTime and iMessage - an error occurred during activation I couldn't log in to FaceTime so I did a factory reset of my MacBook. It worked for a brief period of time and then suddenly it just logged out.  I believe it might have been after iCloud synced with keychain or after I changed my local host name and computer name.  I have seen other users facing this issue but no solutions. Is there a troubleshooting guide or should I just contact Apple support since I can't use their service without activation to my Mac? I'm  trying to create a FPS game in blender game engine. When I do KeyBoard[Spacebar] sensor and hook it up to a simple motion of z +1 or something like that, the guys pops up really fast as if he didn't have any motion between being on the ground and being in the air. Is there a way to make a more realistic, more slow jump in BGE? Stern-Brocot tree where each node has two fathers Getting / setting file owner in C# Make tools indestructible in Minecraft Copy files from a list to a folder What are the best strategies for assessing if a journal is a &quot;vanity&quot; or &quot;predatory&quot; journal that should be avoided (both for publishing in and reviewing for)? For example, how would one go about determining if a journal/publisher belongs on ? Where such a term would reference the location/time of an object, almost like it was of a property of the object. That is to say, if a duck is red, blue, yellow etc, we describe it has having a certain colour. If it's a nanometre, or 10km big, then it's property of size.  Now I know that where/when an object exists an object isn't a property of an object, but it is something unique to that object, so I think it would be useful to have a shorthand for 'geographical location', and 'time of existence'.  There are terms describing both time and location, such an event, or rendezvous (which I think is used to describe the when and where of a meeting between two humans) but I wan't a term that just describes one of each.