Mod arithmetic and divisibility
$pq\mid pn^q+qn^p+kn$ for some $k,\,$ if $p,q$ are primes
Why are moderators now required to report underage users? Just today (December 2, 2020), a  was enacted, which requires moderators to report users that they find to be underage:  If you find a user claiming to be under 16 escalate it to us through the &quot;Contact Community Team&quot; button and select the &quot;underage user&quot; template - this will flag the on-duty CM for action so we can investigate and, if deemed necessary, delete that account and all personal data associated with it. [...] This policy only applies to sites where you are a moderator. If you see things on a site where you’re not, there is no obligation to escalate.  Being part of the , moderators are required to follow the instructions there, and not following them is considered a violation of the moderator agreement. However, this contradicts a , which states (bold added):  Users and moderators are not legally responsible for underage users and are under no obligation to report them to us. If out of concern you would like to report it, [...]  As part of the re-enaction of the policy on December 2, the text &quot;and moderators&quot; in the above quote was edited out of that statement. Why are moderators now required as per policy to report underage users that they come across? Is there a legal explanation as to why SE's stance on this changed? I'm aware of  from a then-employee, which stated that moderators are expected, but not required as a condition of remaining a moderator, to report underage users. However, the new policy requires reporting them. Why? An example of a case where a moderator may not want to report an underage user is if the user claims to be from an EU country that has reduced the required age from 16. While SE's Terms of Use specify a blanket limit of 16 to comply with regulations in all EU countries, individual member states do have the ability to reduce the limit, so long as it's not below 13. There is no law violation if, say, a 15-year-old user from an EU country that has reduced the age limit to 14 registers, so a moderator may not feel like reporting them (since in that case they're merely enforcing the Terms of Use, which they're not otherwise expected to do).  The policy was recanted a few days after it was originally enacted on October 15, 2020, but was enacted again on December 2 after minor revisions following a review among moderators. The same question still applies to the revised policy, however. Already the early papers on supergravity were written using computer algebra software to do some calculations. What modern packages do people normally use for doing such calculations? Of course Mathematica and presumable a lot of other programs can be made to do such calculations, I am wondering if there are special packages or tutorials how to do such calculations in them. Understanding QGIS buffer tool units I  have had no luck getting the buffer tool to accept anything but degrees as units of measure.  I have found lots of stuff saying the layer needs to be reprojected and saved but it hasn't worked at all for me.   Is there a way I could create a buffer without using ftools or at least force the units to meters somehow?  As a workaround I converted meters to degrees (lat) and used that but the final product needs to be as close to reality as possible.  Things I've tried:   setting every unit option I could find to meters (where possible). setting everything to NAD83/Maryland (data is for Washington, DC) and saving it as such (as layers in ESRI shape files). reimporting the reprojected layers setting relevant layers to Google Mercator   The was tried followed by creating a buffer. Many were tried in combination. QGIS 1.7.3 Slackware64 current (qgis from SBo-13.37 repo, tried on multilib and plain 64it with same results) I've been battling the following two questions for more than a day today.  Write a regular expression (comprised of {a, b}) that contain at least two b and do not contain abb. Write a regular expression (comprised of {a, b}) that contain abba and do not contain baa.  For the first part I wrote a basic one to start off with that doesn't handle the must two-b: b* OR a* OR (a+ AND b)* OR a*  I ran a few &quot;truth tables&quot; inputs over it and it seems ok. But the moment I add the requirement, things go haywire. Mostly because when pushing in those &quot;b&quot;s, you can suddenly use the OR to break things up. Same thing on the second one.... Any help would be greatly appreciated! Norah Practical way to implement prevention of IP Spoofing I am an undergraduate Computer Science student and was hoping to gain some knowledge of ways to help prevent IP spoofing but all the resources I have tried out elaborate this concept in a theoretical way. I want to try out my hands at one of the techniques like:      How do I simulate this whole situation in my own system were I myself am the attacker and I myself have to defend it? And once I have gained an understanding of it, then how do I start translating that into programming terms? HP PSC-2100 can't seem to get xsane and HPLIP (printing working) How can I work around this TikZ bug: (\x)^2 and \x^2 produce different results in TikZ plot? I have some files with TikZ graphics that have suddenly changed appearance since I upgraded to PGF-2.10.  Here is a minimal example:  \documentclass{minimal} \usepackage{tikz} \begin{document} \pgfversion\par \begin{tikzpicture} \draw[blue] plot[domain=-1:1] (\x,{\x^2 + \x^3}); \draw[xshift=4cm,blue] plot[domain=-1:1] (\x,{(\x)^2 + (\x)^3}); \end{tikzpicture} \end{document}   In PGF 2.00 I had this:    while in 2.10 I have this:    The one on the left in PGF 2.10 looks like the graph of y=x^3 but could also be y=x^3 + x|x|.   This has been  on sourceforge and  on the pgf-users mailing list.  Although I haven't checked myself yet, the bug remains open and some of the commenters below report that problems still exist in the CVS version.   Geoffrey Jones notes the bug is in the 2.00 CVS version:     Hi Matthew, not an answer, just an FYI   that's too large for the comment box.   My compile of your code through pgf   v2.00 produces the result you see with   v2.10, above:       I.e., the difference you observe seems   to pre-date v2.10.   There is a workaround by inserting parentheses.  But since I have so many old lecture files I'd rather find a solution that doesn't involve rewriting my TikZ code.  And I'm squeamish about using the CVS bleeding edge code even if it were fixed, since I don't want to introduce other problems.  Ideally I'd like a simple patch that I can stick at the preamble, or just fix one file in the PGF distro. Accented letters with IM FELL fonts How to make Unicode charset in cmd.exe by default? SD Card showing weird file names and files are lost I just plugged my SD Card to my PC after a long videography day, and I suddenly got this problem:    It is also not showing all the videos I took on my camera so what is the solution? In an ideal circuit, How can there be a current b/w points a &amp; b, when there is no potential difference and thus no electric field between a &amp; b? If there is no current, then where does current across the resistor come from, because that means no charge is coming from the battery (?). What is the complexity of finding SHA-1 collisions? Given the , what is the complexity of finding a SHA-1 collision?  Marc Steven's  is still detailing about 260. Does the previous complexity still hold? Annuity notation in LaTeX I'm looking for the best / friendliest way to reboot my rooted android 4.1.1 device. I found these solutions so far:   su -c "reboot" - Causes problems with wifi after restart on my device... I read that this can cause a currupt file system in some cases... Doesn't work via ssh for me. toolbox reboot - Same concerns here, but works via ssh. reboot -d 8 -f - causes problems after restart e.g. some apps wont start busybox killall system_server - "Hot Reboot" (not really a system restart) start|stop - Starts/stops Android Runtime (not really a system restart)   What is the device doing exactly when I'm pushing the (hardware) power button? I guess that's the most friendly way. This might be a bizarre but crucial question, can I fully trust leaving my laptop in repairs (Genius Bar) while they have full access to it ?  I recently went to the genius bar to get my display fixed, and apparently they asked for my laptop's password just in case they need some "testing" after they're done. Can't they do that as a guest account ?  I got sensitive information on my laptop such as passport copies etc, as well as passwords saved in Safari's keychains for my bank account, paypal, amazon etc ..  The service is due later on today, shall I change my password and ask them to contact me directly if they need something specific ?? They're going to fix in 3 hours so I'll be in the mall whilst they finish. Proving the Cauchy-Schwarz inequality by induction Can fresh pasta sheets be used to assemble a lasagne, then left in the fridge overnight before baking? Or will this make them mushy or otherwise degrade them?  I have recently gotten into making fresh pasta, and I want to prep a lasagne the night before. I have done this before with store-bough dried noodles, but I'm not sure if doing this will have a negative effect on fresh, more delicate pasta. Covering estate tax on US assets for non-resident alien I am a non-resident alien holding a brokerage account in the USA but residing outside the USA. My country does not have an estate tax treaty with the USA. So my estate is liable for a significant estate tax up to 40%. Is there any way to avoid or to cover this tax? I thought of buying term insurance for myself, but I am not sure whether US companies will sell term insurance to a non-resident. I want to buy insurance from a US company because I want the death benefit to be in USD. Can someone suggest as to what the best way to approach this issue is? US / Mexican border data I'm interested in locating free GIS shapefile data representing the US / Mexican border. I have found a point layer depicting the border crossing points but I'm interested in a polyline feature representing the actual border. I would like to know where gravity gets its energy to attract physical bodies?  I know that the law of conservation states that total energy of an isolated system cannot change. So gravity has to be getting its energy from somewhere, or else things like hydropower plants wouldn't be able to turn the power of the falling water into a spinning rotor.  Just to be clear, Lets create an example:  Lets say we have two objects with equal mass close to each other. So gravity does its job and it pulls each other closer, this gets turned into kinetic energy. This is where I'm lost. According to the law of conservation energy can't be created or destroyed and the kinetic energy comes from the gravitational pull so where does the gravitational pull gets its energy.  If that energy isn't being recycled from some where else then that means you have just created energy, therefore breaking the law of conservation.