Charge is relativistic invariant. What does it mean?
How can we prove charge invariance under Lorentz Transformation?
How to use aes-encryption in PostgreSQL? I tried aes-encryption by using following statement:  SELECT encrypt('test', 'key', 'aes');   which worked, but I am not able to decrypt the value. I inserted it in a field of datatype bytea but I'm not sure if that was the right way.   SELECT decrypt(pw, 'key', 'aes') FROM table WHERE ID = 1;   gives me the error     ERROR:  function decrypt(bytea, unknown, unknown) does not exist   LINE 1: SELECT decrypt(pw, 'key', 'aes') FROM tabelle WHERE ID = 7;                  ^   HINT:  No function matches the given name and argument types. You might need to add explicit type casts.   Does that really mean that encrypt() is an existing function, but not decrypt()? How else could I retreive aes-encrypted values? I just made some minor edits to the text of .  I didn't edit the tags at all.  When I completed my edits, my edit showed as:    Now, I think those tags were present before I started my edit, and so were probably slipped in by the OP in their edit grace window.  I have no problem with that tagging, but I don't like seeing edits attributed to me that I didn't make.  So, what the heck? Every partial order can be extended to a linear ordering How do I show that every partial order can be extended to a linear ordering?      I think that I manage to prove that claim for finite set, how can I prove it for infinite set?  Thank you. Attributive nouns vs. of-genitive "The following packages have been kept back:" Why and how do I solve it? Chain skip happening seemingly at random with a new chain Who can knight you so that the knighting 'sticks'? Motivating scenario:  I'm a swell upstanding guy, so Ser/Lord X, an acquaintance of mine, knights me. So I walk into my village tavern; the barkeep asks "What'll it be, friend?" and I tell him "That's 'Ser' to you now. I have been knighted by X!" He sneers and goes "well then, X can call you Ser if he likes."  Actual Question:  What about a person's being knighted makes the knighting 'stick'? Is it the identity/standing of the knighter (is that a word?) ? Is it the fact that many other knights walk around telling people that the new guy is also a Knight? Is it the public nature of the knighting?  The  says  about knighting:     This usually happens when a squire reaches adulthood and his master   judges him worthy of accepting the responsibilities of a knight. A man   who has not been raised in the knightly tradition can also be made a   knight as a reward for service. This is often granted to soldiers or   other smallfolk who have shown bravery or performed a great feat.   Notes:   I'm only asking about Westerosi Andal-culture Knights, around the time of Robert I Baratheon's rule. As a non-native speaker, I cannot grasp any difference between the expressions "here we go" and "there we go": both expressions seem to underline an event that is going to happen immediately.  Is there any subtle usage detail that I am missing? Meaning of U suffix finding the index of a max value in R yum install error I can't run a yum command on my server without getting this:   CRITICAL:yum.cli:Config Error: Error accessing file for config file:///etc/yum.conf   This is what my yum.conf looks like:  # This is the fedorafaq.org yum.conf for Fedora Core 5. # # Note that you also need the rest of the configuration # as described at http://www.fedorafaq.org/#yumconf  [main] cachedir=/var/cache/yum keepcache=0 debuglevel=2 logfile=/var/log/yum.log exactarch=1 obsoletes=1 gpgcheck=1 plugins=1 metadata_expire=1800  # PUT YOUR REPOS HERE OR IN separate files named file.repo # in /etc/yum.repos.d   This is what my yum.repos.d looks like:  fedora.repo fedora-updates.repo fedora-updates-testing.repo   The permissions on those files are 0666 and it won't allow me to make them root:root How to use iSight webcam without activating the green light? Recently a the Dutch government advised to put a tape on your webcam to prevent hackers from taking pictures and video using your device ().  The build in iSight camera in Apple laptops have a green light next to the camera, this light turns green when you use the camera.  Is it possible to use the camera without the activation of the green light? Personally I think the green light turns on when the sensor requires power and this is hardwired in the hardware. Am I wrong?  I have found similar questions on stackexchange, but I found non that answer this specific question. Scan vs. Map vs. Apply Failed to mount Windows share: Invalid argument A very similar question has been asked before by robazefa, but no one answered it. For the last month or so, my Ubuntu 14.04 LTS box has been been unable to open a couple of folders shared from external drives on a PC running Win 8.1 on a home network.  Through Files on the Unity desktop, I can browse the network, access the workgoup, access the Win 8.1 box, see and access its shares except the folders on its external drives.  They appear on the list and I could access them without a problem a couple of months ago, but now I get a dialogue box with Unable to access location - failed to mount Windows share: Invalid argument message, with only the option to click OK.  These folders are readily accessible now from other Win 7 and 8 PCs on the network, but the same Invalid argument error now appears on the only other Linux box on the network which runs Mint Cinnamon.  My question is which argument is in invalid and how can I validate it? Replace a long string with the sed command: Argument list too long error I'm trying to execute this command  sed -i -e "s/BASE_64/$BASE_64/" FILE_NAME   where $BASE_64 is a base 64 representation of a file content.  sed gives me an error since the string is too long.     Argument list too long   How is it possible to avoid this error? Installing Crystal Reports 8.5 on Windows 7 I have successfully installed Crystal Reports 8.5 on my Windows 7 desktop, but when I try to launch the application i get this:    Any experience with this?  Besides the obvious "update to as newer version", does anyone have any suggestions? Reclassifying raster layer with certain colors for value ranges in QGIS? I'm using QGIS. I want a raster layer with 6 different colors each color representing a certain value range (e.g. -1 to 0 red, 0 to 0.2 orange).  In the layer style menu I can only approximate colors. This Community Wiki question is designed to be the "canonical question" for questions asking how to upgrade one's device to a new Android version.   I want to get a newer version of the OS for my Android device. How can I do that?  See also: How to create a batch job, numbering images (writing text on them) from 1 to 100 in Photoshop? Looking to create a 100 images that would have their appropriate numbers written on them.  Since I`ll be most likely making changes to the template in the future I figured it would be better to automate it somehow.  Is there a simple solution to this problem? When writing (a blog post, script, etc..) what is the proper way to indicate two or more instances of a single letter? For instance, in Monty Python's Bookshop Sketch:     C: I wonder if you might have a copy of "Rarnaby Budge"?      P: No, as I say, we're right out of Edmund Wells!      C: No, not Edmund Wells - Charles Dikkens.      P: (pause - eagerly) Charles Dickens??      C: Yes.      P: (excitedly) You mean "Barnaby Rudge"!      C: No, "Rarnaby Budge" by Charles Dikkens.  That's Dikkens with two Ks, the      well-known Dutch author.      P: (slight pause) No, well we don't have "Rarnaby Budge" by Charles Dikkens      with two Ks, the well-known Dutch author, and perhaps to save time I      should add that we don't have "Karnaby Fudge" by Darles Chickens, or      "Farmer of Sludge" by Marles Pickens, or even "Stickwick Stapers" by Farles      Wickens with four M's and a silent Q!!!!!  Why don't you try W. H. Smith's?      C: Ah did, They sent me here.   I had always believed that plural never uses an apostrophe before the 's' (it's only used for possession), but I have rarely seen in written material the format "four Ms". (On a side note, whoever wrote  also used "two Ks".)  On a side note, and perhaps this should be a separate question, if a Compact Disc is a CD, then two Compact Discs would be two CDs right? (I see "CD's" written everywhere)