How can I invite my Facebook friends to Stack Overflow? Is it possible?
Since we're all into this OpenID thing, I think it would be really useful (and quite easy) to implement a friend invitation feature that grabs a list of friends from one's webmail contact list with an option to choose who to invite to SO, SF or SU. Something in the line of Facebook's friend invitation and recommendation feature.
$n,a,b \mathbb \in \mathbb Z^+$ , such that $n\mid a^n-b^n$ ; to show $n\mid \frac {a^n-b^n}{a-b}$ How do I boot Windows 8 into Safe Mode? I have Windows 8 Enterprise x64. It's installed a virtual machine. After trying to update VMWare's guest extension it black screened. After resetting it, now the virtual machine won't boot. It just says "automatic repair couldn't repair your PC"   Everything I do ends with an error or it coming back to this screen. If I go to Troubleshoot > Advanced Options > Start up settings and then go to Safe Mode, all it will do is say "preparing automatic repair" and then "diagnosing your PC" and then will come straight back to the "automatic repair couldn't repair your PC" screen. It's as if it doesn't even attempt to go into safe made.   Is there anything else I can do before I reformat? When do relativistic effects need to be explicitly included? Why is the accountsd process eating so much CPU? Big tilde in math mode How do I get a really wide tilde?  I need to cover at least  abcdefghijklmnopqrstuvwxyz  The \widetilde command does not work. Nor using \stackrel with \sim. Why do non-constant periodic functions have no limit at infinity? I'm looking to get data such as Size/Capacity, Serial No, Model No, Heads Sectors, Manufacturer and possibly SMART data. I have an issue which I could not solve, although I tried and I got some help on R forum.  I am trying to calculate Mahalanobis distances on a data.frame, where I have several hundreds of groups and several hundreds of variables. Whatever I do, I get the system is computationally singular: reciprocal condition number error.   It is clear that it is singular, but is there any way to get rid of it and run Mahalanobis? Should I forget solve this using another approach? If yes, then what else to use?  I have uploaded the data file to my :  It is a tab delimited txt file with no headers.  I was working with the R StatMatch Mahalanobis (also tried stats Mahalanobis) function. I have a deadline for this project (not a homework!), and I could always use this function, so I thought I will be able to keep the calculations short, but now I am lost.  Migrated . Do Hogwarts Houses have quotas? Not a year goes by where we don't see at least one person Sorted into each House, and it's usually a fairly even distribution.  The Sorting Hat doesn't get a chance to study the mind of each child before Sorting, so it can't Sort them relative to each other (top X in smarts go to Ravenclaw, 4 bravest to Gryffindor, etc)  What would happen if a Sorting occurred where all the witches/wizards were extremely intelligent?  Would they all get Sorted to Ravenclaw?  What if they were all extremely brave?  What if none of them were particularly smart or courageous, but they all wanted power?  We see that there's a fairly small number of beds per room in each dorm, would the Hat stop Sorting people into a House if it knew the House had no more beds?  If so, could Harry Potter have ended up in Hufflepuff if his last name had been 'Zimmers'? Add different materials to different parts of a mesh? Clipboard for copying and pasting files in command line? In Bash, suppose I visit a directory, and then another directory. I would like to copy a file from the first directory to the second directory, but without specifying the long pathnames of them. Is it possible?   My temporary solution is to use /tmp as a temporary place to store a copy of the file. cp myfile /tmp when I am in the first directory, and then cp /tmp/myfile . when I am in the second directory. But I may check if the file will overwrite anything in /tmp.  Is there something similar to a clipboard for copying and pasting a file? Persist sort/filter selections Let $a,b,c\in\mathbb{R}^*_+$, $abc=1$.  How can i show that $\left(a-1+\frac{1}b\right)\left(b-1+\frac{1}c\right)\left(c-1+\frac{1}a\right)\leq1$ ?  I got $\left(ab-b+1\right)\left(bc-c+1\right)\left(ca-a+1\right)\leq abc=1$, but i can't go any further ...  If i expand it :   $2-ab-\frac{b}a-c-ac-\frac{a}c-b+2a+\frac{2}a-bc-\frac{c}b-a+2b+\frac{2}b+2c+\frac{2}c-4$  Which gives using $c=\frac{1}{ab}$ :   $5ab-\frac{b}a-\frac{1}{ab}-a^2b+\frac{1}a+b+\frac{1}b-2$ What is a "Nested Quantifier" and why is it causing my regex to fail? I have this regex I built and tested in regex buddy.  "_ [ 0-9]{10}+ {1}+[ 0-9]{10}+ {2}+[ 0-9]{6}+ {2}[ 0-9]{2}"   When I use this in .Net C#   I receive the exception  "parsing \"_ [ 0-9]{10}+ +[ 0-9]{10}+  +[ 0-9]{6}+  [ 0-9]{2}\" - Nested quantifier +."   What does this error mean? Apparently .net doesn't like the expression.  Here is the regex buddy so u can understand my intention with the regex...  _ [ 0-9]{10}+ {1}+[ 0-9]{10}+ {2}+[ 0-9]{6}+ {2}[ 0-9]{2}  Match the characters "_ " literally «_ » Match a single character present in the list below «[ 0-9]{10}+»    Exactly 10 times «{10}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {1}+»    Exactly 1 times «{1}+» Match a single character present in the list below «[ 0-9]{10}+»    Exactly 10 times «{10}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {2}+»    Exactly 2 times «{2}+» Match a single character present in the list below «[ 0-9]{6}+»    Exactly 6 times «{6}+»    The character " " « »    A character in the range between "0" and "9" «0-9» Match the character " " literally « {2}»    Exactly 2 times «{2}» Match a single character present in the list below «[ 0-9]{2}»    Exactly 2 times «{2}»    The character " " « »    A character in the range between "0" and "9" «0-9»   In short...  What is a Nested quantifier? If every real-valued continuous function is bounded on $X$ (metric space), then $X$ is compact. Let $X$ be a metric space. Prove that if every continuous function $f: X \rightarrow \mathbb{R}$ is bounded, then $X$ is compact.  This has been asked before, but all the answers I have seen prove the contrapositive. Realistically, this may be the way to go, but is there way to exhibit an unbounded continuous function (under the assumption $X$ is not compact) without appealing to results beyond introductory real analysis (e.g., the solution I've seen involves the Tietze Extension theorem)?  Because we're working with metric spaces, it's clear that the assumption that $X$ is noncompact (towards proving contrapositive) will lead us to extract a sequence of points in the space with no convergent subsequences. But how can we infer the existence of an unbounded continuous on the space knowing only about some sequence of points in this space (without using anything too advanced)? My friend and I are planning a vacation to Ireland later this year. We'll be there for a week, flying into Dublin and then renting a car and driving around the country.  Both of us are 23. Are there any age restrictions on renting cars in Ireland? What would be the cheapest/best option for us? I'm trying to find the name of a book I had as a kid back in the 80's/90's that was a collection of science fiction short stories and in particular one story in it.  The book: I remember the cover being mostly orange with the face of an alien taking up most of the cover. Scaly looking 'grey' style alien with hooded green eyes. They may have also been a 60's/70's style space ship in the background with a man and woman.  The story: Was set after all human life had ended in a great war and the story followed one of the many autonomous bombers still flying the skies carrying out their missions repeatedly bombing already leveled cities. At least that's how I remember it.  Any help/clues you can give would be much appreciated as I'd love to share these stories with my kid.  Some other stories it had, if any of these can be identified it might help me find the book:   Two guys talking in a room and one give the other a wooden carving of an apple and starts telling him the history of the object and how it's used to hypnotise people who hold it as they can't resist stroking it and it puts them in a catatonic state. A bunch of robots/machines wandering the post-apocalyptic country side, free of their duties to mankind. Their adventure comes to an end when they run into a hermit living in the country and their programming kicks in and they immediately become his servants. A story about first contact with an alien race, the aliens come to earth and land at the coordinates of an air-force base but upon arrival there is confusion as the humans cannot see the aliens and the aliens cannot see the humans. The aliens complain that they've been tricked and that their ship is sinking. The humans think this is strange until they realise the aliens are incredibly small and have landed in a puddle on the airfield. Is "of" instead of "have" correct? How do you run a Python script as a service in Windows? Derivation of $E=pc$ for a massless particle? In classical mechanics, massless particles don't exist because for $m=0$, $p=0$.  The relativistic relation between energy, mass and spatial momentum is: $E^2= (pc)^2 + (mc^2)^2$ . So it is said that setting $m=0$ in the first equation you get $E=pc$.  How could setting $m=0$ in that equation give you $E=pc$ whilst $p$ appears in the equation and we know $p=γmu$? If you set $m=0$ you will have indeterminacy due to "$γm$". It seems to me like we are doing a "trick" in order to get the $E=pc$. Perhaps there is another proof for this relation?