Proof of odd number of divisors of a perfect square
$m$ is a perfect square iff $m$ has an odd number of divisors?
Hiding some slides in student handouts in Beamer I am preparing lecture slides for a class. I would like to hide some of the slides from the students. As an example, I would like to be able to compile students.pdf which has only student slides 1 and 2 (i.e., "teacher slide" is hidden); but teacher.pdf which has all three slides.  \documentclass{beamer}  \begin{document}  \begin{frame}{Student slide 1} blah blah blah \end{frame}  \begin{frame}{Teacher slide} secret stuff not to be shared with students \end{frame}  \begin{frame}{Student slide 2} blah blah blah \end{frame}  \end{document}   How would I do this in beamer? In a regular document, e.g., article, I would use the comment environment.  I feel that the approach in  is overkill for my needs. In C#, should I use string.Empty or String.Empty or "" to intitialize a string? In C#, I want to initialize a string value with an empty string.  How should I do this?  What is the right way, and why?  string willi = string.Empty;   or  string willi = String.Empty;   or  string willi = "";   or what? "In" and "on": How can I decide which one to use for vehicles? Examples:   In a car, van, etc. On a bus, boat, motorcycle, etc.   How can one decide which preposition to use? Is memorization the only way or is there a better way?  Note: People generally explain this by either distinguishing between open and closed vehicles or between large and small vehicles. However, the examples I've given defeat both explanations. Segmentation fault on large array sizes On my homepage, I'm using this method to hide my email from spam bots:  &lt;a href="admin [at] example.com"    rel="nofollow"    onclick="this.href='mailto:' + 'admin' + '@' + 'example.com'"&gt;Contact me&lt;/a&gt;   What do you think about it? Is it effective? What other methods do you know or use? What happened to Finn's blaster at Maz Kanata's? When entering, we see that Finn has the blaster that was given to him earlier:    However, when the fighting begins, Finn tells Maz that he needs a weapon and no longer has his blaster with him.  It seems unlikely to have been lost in the first shots, given how it is secured across his body.  Also, Han and Chewie didn't lose their weapons and they are arguably less secure.  Now, when the team gets to the Resistance base, Finn again has his blaster:    So where was this blaster during the battle? Orange squares appearing on render? Downloading all my questions with the answerer names I am writing several papers in which I use answers which I received in various StackExchange websites. Naturally I would like to acknowlege and thank the SE members that gave the useful answers. But there are many such answers, and each answer is relevant to a different paper.   So, I would like to download all the questions that I asked in the various SE websites, including the answerer names, to an Excel worksheet in which I can organize the questions by subject.  Is this possible? Elliptic Curves of different forms Looking at  to find a safe curve, I find that most curves described here are of a different form from that generally used.  In , for example, FpCurves take curves of the form $y^2 = x^3+ax+b$ (Weierstrass), whereas the (safe) curves found on the above linked have different forms, such as $y^2 = x^3+ax^2+x$ (Montgomery) - how do I translate between the two? How do I use the second form of curve with, for example, Bouncy Castle?  (Or do I simply have to accept that no safe curves of the Fp form exist?)    What else have I tried? Guide to Elliptic Curve Cryptography (Hankerson et.al.) covers curves of the forms $y^2 = x^3+ax+b$ for fields with characteristic > 3, and only offer alternatives (that are not interchangable with the safe curves, either) for lower characteristics, that are not very useable in my situation. Even then, some curves on the safe curves website are of forms that I cannot immediately find explained anywhere. I am pretty sure that most of us here, or at least those do graphic design for living, have found themselves in following situation:   You agree with a client to do the design, agree on price, schedules, formats etc… You work hard, make adjustments, collaborate with client; everything goes well in the beginning. At some point you realise that the client does not listen your professional advice regarding design and prefers his/her own ideas that might not look so professional (choice of fonts, colors, odd choices of elements, shapes etc…). No matter how hard you try, the client is persistent and will not accept the designer’s advice. You get back to work, try to make the best out of it, and the final result is not so good, mainly because you had to stick to the client’s wishes. Work is shipped, payment done, and you don’t want to include this work in your portfolio because it is not good. After all, it is not your work, it is something that was physically created by you as a designer, but the ideas, concept, story, and message came out as a result of nonprofessional person, your client.   Ok, they pay for it, and as long as they are happy this is fine. But, the more compromises you make, the more time you spend working on bad design. If you are a young designer on a quest to get recognition, you don’t want to work just for the sake of money and then face the lack of good design in your portfolio.   Maybe at the beginning of your career you don’t care that much, but later if life this might be a big issue. At some point you will be approached by a big client that might offer you long-term contract, but first they will want to see your work. No point explaining to them what you did and why you made so many compromises.   They will not be interested in that.  Every project is precious as your time and you want to do use it wisely and produce great work.   How would you deal with such a situation? Is a DSL splitter required, if only a Modem is attached to the line? SVG for images in browsers with PNG fallback There are 100 ropes in a bag. In each step, two rope ends are picked at random, tied together and put back into a bag. The process is repeated until there are no free ends. What is the expected number of loops at the end of the process? How many integers between $1$ and $10^4$ contain exactly one $8$ and one $9$? I have this problem: How many integers between $1$ and $10^4$ contain exactly one $8$ and one $9$?, but i dont know if $18, 19, 28, 29...$ serve, else it could be $8$ y $9 = 2$ numbers, help please. How to get back Windows 10 [UEFI] after Legacy installation of Fedora 24? Suppose we have a magnetic field directed into the computer screen. Assume that there is no gravitational field. Now suppose we have a stationary positively charged particle in the magnetic field. The magnetic force is given by $$\mathbf{F}=q\mathbf{v}\times\mathbf{B}$$  Since $\mathbf{v}=0, \mathbf{F}=0$.  Now pick a reference frame moving to the left with constant velocity. In this frame, the particle is moving to the right with constant velocity. So, the magnetic force is directed upwards.  From what I've learnt in physics, forces are independent of choice of reference frames as long as the frames are inertial. But in the 2 inertial reference frames I have chosen, I get 2 different magnetic forces. How do we reconcile this? Showing this metric space is complete Let $X=(0,1]$ and $d(x,y)=\left|\frac{1}{x}-\frac{1}{y}\right|$. I've proven $(X,d)$ is a metric space but I don't know how to show its completeness. How can I do that? Does entanglement not immediately contradict the theory of special relativity? Does entanglement not immediately contradict the theory of special relativity? Why are people still so convinced nothing can travel faster than light when we are perfectly aware of something that does? I am looking for an example such that in a pre-Hilbert space $H$ we have for a subspace $U$ that  (i) $\bar{U} \oplus U^\perp \neq H$  (ii) $ \bar{U} \neq U^{\perp \perp}$  Since finite and closed subspaces will probably not do it, I am not good at inventing nice examples. Does anybody here have a few at hand? Looking at moving my laundry upstairs, and the right answer is to combine two adjacent closets to get the width and move one of their walls a foot or two into the kitchen to get the depth.  The kitchen floor is 10-inch-square tiles. It would be sort of nice if that continued on into the laundry closet. I do have a full bundle of spare tiles in the basement.   Question: Could/should I plan on the new wall coming in on top of the existing tiles (presumably having to drill to secure the footer without shattering them), or should I plan on removing the ones under the footer and fitting cut pieces back in afterward?