Show that if $a = a^{-1}$ then $a=1$ or $a=-1$
If $a \cdot a = 1$ then $a = 1$ or $a = -1$
WhatsApp for Ubuntu Phone? Does someone know if there already is a WhatsApp Version for Ubuntu Phone? I decided to install Ubuntu on my Android, but I don't want to use my phone without WhatsApp. When should I not kill -9 a process? ASP.NET MVC controller actions that return JSON or partial html How do you handle multiple instances of setTimeout()? What is the most recommended/best way to stop multiple instances of a setTimeout function from being created (in javascript)?  An example (psuedo code):  function mouseClick() {    moveDiv("div_0001", mouseX, mouseY); }  function moveDiv(objID, destX, destY) {    //some code that moves the div closer to destination    ...    ...    ...     setTimeout("moveDiv(objID, destX, destY)", 1000);    ...    ...    ... }   My issue is that if the user clicks the mouse multiple times, I have multiple instances of moveDiv() getting called.  The option I have seen is to create a flag, that only allows the timeout to be called if no other instance is available...is that the best way to go?  I hope that makes it clear.... I need a poll inside my content types.  Sometimes the users create an article and like to create a poll directly into the node they created. They don't want to create an extra poll with no connection to the original article.  So how can I get the poll functionality inside a different content type? Ignore .DS_Store and Icon files in a folder with Cocoa NSFIleManager How to connect Selenium to an existing browser that was opened manually in java or create semi automated tests? I want to achieve some use cases in which:  I want to perform some tasks that require manual intervention before kicking in automation execution. For instance, I need to manually launch the browser, navigate to the desired page, perform some manual tasks like entering captcha manually and then run the automation script to continue from there.  Debugging – Let's say we are working on a test script for a certain page (product checkout) in the application. But the script to reach that page (add to cart) is not ready yet. We can manually launch the browser and navigate to that page and then run the automation script.  Can someone help me to achieve this type of scenario? Are there non-legal consequences for wizards that meddle with time? Question:  Is it possible to get multiple correct results when evaluating an indefinite integral?  If I use two different techniques to evaluate an integral, and I get two different answers, have I necessarily done something wrong?    Often, an indefinite integral can be evaluated using different techniques.  For example, an integrand might be simplified via partial fractions or other algebraic techniques before integration, or it might be amenable to a clever substitution.  These techniques give different results.  For example, looking over a few other questions on MSE:      From : evaluate $$ \int x(x^2+2)^4\,\mathrm{d}x. $$    Via the substitution $u = x^2+2$, this becomes $$ \int x(x^2+2)^4\,\mathrm{d}x       = \frac{1}{10}x^{10} + x^8 + 4x^6 + 8x^4 + 8x^2 + \frac{32}{5} + C.     $$ However, multiplying out the polynomial and integrating using the power rule gives $$ \int x(x^2+2)^4\,\mathrm{d}x       = \frac{1}{10}x^{10} + x^8 + 4x^6 + 8x^4 + 8x^2 + C    $$     From :  evaluate   $$ \int \frac{1-x}{(x+1)^2} \,\mathrm{d}x. $$    Simplifying the integrand using partial fractions then integrating gives $$ \int \frac{1-x}{(x+1)^2} \,\mathrm{d}x       = \frac{-2}{(x+1)} - \ln|x+1| + C.    $$ Via integration by parts, we get $$ \int \frac{1-x}{(x+1)^2} \,\mathrm{d}x       = \frac{x-1}{(x+1)} - \ln|x+1| + C.    $$     From : evaluate   $$ \int \frac {\tan(\pi x)\sec^2(\pi x)}2\,\mathrm{d}x. $$    Using the substitution $u = \sec(\pi x)$, this becomes $$ \int \frac {\tan(\pi x)\sec^2(\pi x)}2\,\mathrm{d}x       = \frac {\sec^2(\pi x)}{4\pi} + C.    $$ Using the substitution $u = \tan(\pi x)$, this becomes $$ \int \frac {\tan(\pi x)\sec^2(\pi x)}2\,\mathrm{d}x       = \frac {\tan^2(\pi x)}{4\pi} + C.    $$ In The Dark Knight Rises, at the beginning of the film Bane kidnapped a guy from the plane, then he drew blood from the guy he kidnapped. And then throughout the movie I didn't see any news regarding this kidnap scene. But, before the end of the movie we find out that the guy kidnapped by Bane was Dr Pavel. Bane needed him to convert the fusion project into a nuclear bomb and Dr Pavel was the only guy who could have done it.   But I don't understand, why did he draw blood from Dr Pavel? No more disk space: How can I find what is taking up the space? I've run into a problem on one of my servers running 16.04: there is no disk space left.  I have no idea what is taking up the space. Is there a command to list the current directory sizes, so I can traverse and end up in the directory taking up all the space? What's the function of the ~ bitwise operator (Tilde) I've been trying to develop an intuition based understanding of Bayes' theorem in terms of the prior, posterior, likelihood and marginal probability. For that I use the following equation: $$P(B|A) = \frac{P(A|B)P(B)}{P(A)}$$ where $A$ represents a hypothesis or belief and $B$ represents data or evidence. I've understood the concept of the posterior - it's a unifying entity that combines the prior belief and the likelihood of an event. What I don't understand is what does the likelihood signify? And why is the marginal probability in the denominator? After reviewing a couple of resources I came across this quote:     The likelihood is the weight of event $B$ given by the occurrence of $A$ ... $P(B|A)$ is the posterior probability of event $B$ , given that event $A$ has occurred.   The above 2 statements seem identical to me, just written in different ways. Can anyone please explain the difference between the two? Zip all files in directory? Is there a way to zip all files in a given directory with the zip command? I've heard of using *.*, but I want it to work for extensionless files, too. Completeness and Incompleteness Show that $\frac{P(z)}{Q(z)} = \sum_{k=1}^{n}\frac{P(\alpha_k)}{Q'(\alpha_k)(z-\alpha_k)}$ Which has the heavier tail, lognormal or gamma? (This is based on a question that just came to me via email; I've added some context from a previous brief conversation with the same person.)  Last year I was told that the gamma distribution is heavier tailed than the lognormal, and I've since been told that's not the case.   Which is heavier tailed? What are some resources I can use to explore the relationship? Recover data from SD card I have a 2&nbsp;GB Kingston  card which is about three years old. I put it in a reader today in my Windows Vista computer, wrote a 32&nbsp;MB file onto it, safely removed it, and then tried to read it elsewhere. Nothing. Putting it back in the Windows Vista computer it now says:     You need to format the disk in drive F: before you can use it.   What should I do? I have access to many computers and OSes if your recommendations need that. I would be very sad if I lost all the contents of the card. Most of the data is backed up, but there are a few things that aren't. :(  Doing a   # dd if=/dev/sdg of=~/tmp/sd.bin   gives me a 2&nbsp;GB file, and  the file it seems like lots of my data is still there. How can I put it back together? Prove: $\binom{n}{0}F_0+\binom{n}{1}F_1+\binom{n}{2}F_2+\cdots+\binom{n}{n}F_n=F_{2n}$;  I was stuck with this question for a while... Help me please!!! Thanks!!! What is the significance of the name Bleach? The name "Bleach" seems to be having no relevance to the plot unlike most other series. Was it just chosen at Kubo-sensei's whim or does it have some significance? Maybe some cultural significance associated with shinigami, etc. that I am now aware of?