I cannot get new updates
How do I fix a "Problem with MergeList" or "status file could not be parsed" error when trying to do an update?
Should I use "or" or "nor" in the following case? I wasn't forcing myself to say anything, or/nor trying to be funny.   "Or" sounds more grammatically correct to me. But "nor" has more Google results. So I'm confused. Let $M=\big( \begin{smallmatrix} A & B \\ C & D \end{smallmatrix} \big)$. Prove $\det(M)=\det(A)\cdot \det(D-C·A^{-1}·B)$. Let  (shown in matrix blocks) $M=\big( \begin{smallmatrix} A &amp; B \\ C &amp; D \end{smallmatrix} \big)$ a square matrix such that $A$ is invertible and $D$ is a square matrix. I have to prove that  $$\det(M)=\det(A)\cdot \det(D-C·A^{-1}·B)$$  I also have an indication to use it: Consider previously these cases: \begin{align*} A_1 &amp;= \begin{pmatrix} A &amp; 0 \\ 0 &amp; I \end{pmatrix},\\ A_2 &amp;= \begin{pmatrix} I &amp; 0 \\ 0 &amp; D \end{pmatrix},\\ A_3 &amp;= A_1·A_2,\\ A_4 &amp;= \begin{pmatrix} I &amp; A^{-1}·B \\ 0 &amp; I \end{pmatrix},\text{ and}\\ A_5 &amp;= A_3\cdot A_4. \end{align*}   The problem is difficult in general for me and I don't even know how to use the indication. Test for the convergence of the sequence $S_n =\frac1n \left(1 + \frac{1}{2} + \frac{1}{3} + \cdots+ \frac{1}{n}\right)$ Convert track bike to geared Is there any way to convert a track bike to a geared bike? I have a track bike with only the rails for the wheel but I've moved out of the city and there are more hills where I am now living so would like to convert to gears if possible and rather than buy a new bike, save some cash. App Store on Mojave: "We could not complete your purchase. cancelled" Whenever I try to Get then Install any app from the App Store, I get this message:     We could not complete your purchase.  cancelled   I did some searching online, but barely found any useful hits. What is this about?! What is the best way to add options to a select from a JavaScript object with jQuery? First post review queue: answers are questions, questions are answers I believe there is a typo in the  review queue. When reviewing a question, the information message asks the user to review the answer. Take a look at the image below.    Similarly, when an answer is posted in the queue, the description box calls it a question instead. Has anyone else noticed this? I need to know the ip address of another machine in a lan network.  What is the Windows command for getting ip address from machine name and vice versa? I posted this at  and got redirected here. This does indeed look like a better place to ask.  I would like to decorate my headlines (section, subsection, etc.) by adding a background color. I would like this box filled with a single solid color to span across the entire typearea.  This picture is a screenshot of an OpenOffice document where the headline has the formating, layout and color I want.    Requirements on a solution   The resulting style is supposed to be used by others, meaning an equivalent latex output to the picture above shall be created by this code:  Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text   \subsubsection{This is a headline}  Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text Some Text  If the section is supposed to be unnumbered one should be using \subsubsection*. LaTeX still needs to be in charge of the whitespace between paragraphs and the blue box.   What I have tried so far  As far as I can google the headline together with the section numbering are a simple paragraph. Latex adds some skips before and after and squeezes in a few commands that modify the font(s).  My ideas revolve around locking this paragraph in a \colorbox. The colorbox macro works like this: \colorbox{color}{the content around which to draw a box filled with the specified color}. My problem is I can't get a grasp on this paragraph.  The easy 80%  My work is based on koma-script and by redefining \othersectionlevelsformat and \(sub)*section. I can draw two boxes, one surrounding the section numbering and another surrounding the section title. However this has 3 open issues:   the upper edges of the boxes are unaligned and the box with the title is slightly larger than the line with the numbering The box around the title does not strech to the right end of the typearea the box around the numbering doesn't grow if the title spans multiple lines (no surprise here)   The hard 20%  I tried to make latex put the section numbering into a \savebox I could access later and put as part of the title. That would eliminate the need for two boxes and solve all three of my problems at once, but that doesn't work. I only get to modify the title before the actual numbering is done. So while I can put the numbering into a savebox, I can't do anything with it until it's too late.  I tried putting the \section ... statement into a colorbox, but it doesn't like that and the document fails to compile with ! LaTeX Error: Something's wrong--perhaps a missing \item. The same holds for saveboxes. I guess colorbox uses those.  I tried putting the \section ... statement in a minipage and put a box around that. This has two issues. 1st: latex doesn't put any empty space above a section. 2nd: not only the section numbering and title have the background but also the empty space between section title and first paragraph.  So how can one hack latex to do a section title formating as shown in the screenshot above? Do "Best by: XX-XX-XX" foods have an expiration date? How long will foods that have "Best by: XX-XX-XX" on the product last past that date?  I have tried looking online, and all I can find is anecdotal evidence, which isn't very assuring for me since there seems to be no specific "x food will expire y weeks after its best by date".  Is there a rule of thumb or some guide out there that can tell me how long a "best by" food will last? Or is it safe to assume that they never expire, since it's not actually labelled on the product? We denote the s value of an ECDSA signature $(r, s)$ on a message $m$ as: $s=\frac{H(m)+xr}{k}$  Assume two ECDSA signatures sharing the same nonce $(r, s_1) , (r, s_2)$ on two messages $m_1, m_2$, that verify under two pubkeys $x_1G, x_2G$.    If the two public keys are equal then the secret keys should be equal $x_1 = x_2$ and we can easily recover the $k$ using the standard attack on nonce reuse. Once we know $k$ we can recover the secret key.  $\frac{H(m_1)-H(m_2)}{(s_1 - s_2)} =\frac{k(H(m_1)-H(m_2))}{H(m_1)-H(m_2)+x_1r - x_2r}$  $x_1 = x_2 \rightarrow x_1r - x_2r = 0$  $\frac{H(m_1)-H(m_2)}{(s_1 - s_2)} =\frac{k(H(m_1)-H(m_2))}{H(m_1)-H(m_2)} = k$  My question is can this attack be made to work if the secret keys are not equal i.e. $x_1 \ne x_2$:  $\frac{H(m_1)-H(m_2)}{(s_1 - s_2)} =\frac{k(H(m_1)-H(m_2))}{H(m_1)-H(m_2)+x_1r - x_2r} = \frac{k(H(m_1)-H(m_2))}{H(m_1)-H(m_2)+ (x_1 - x_2)r}$  If you know either $x_1 - x2$ or $\frac{x_1}{x_2}$  you should be able to compute $k$ as long as $s_1 \ne s_2$.  You can calculate $x_1 - x_2 = \frac{H(m_2) - H(m_1)}{r}$ in case where $s_1 - s_2 = 0$. However this case seems to reduce to the hardness of ECDSA since anyone can compute the pubkey for a new message $m_2$ that verifies under first signature $(s, r)$ using public key recovery.  If $s_1 \ne s_2$ you can compute $\frac{x_1 - x_2}{k}$ which allows you to convert $s_1$ into $s_2$ and vice versa. Time travel short story where dinosaur doesn't taste like chicken I ran across this  and it reminded me of an old short story I read a long time ago.  I read it in a collection of short stories.  It would have been a book because I borrowed it from a school library.   Probably in the 1970s or 1980s.  The book and the story would have been older, though.  Probably from the 1960s or earlier.  In the story, a scientist has a machine that he can use to view the past.  It isn't like a TV or something, though.  It opens a portal into the past that he can look through.  It is very difficult to control, though.  Pointing it at a place and time is likened to working in a hurricane.  The portal jumps and moves about randomly.  The steadier he can hold it, the clearer the past appears.  When it is really steady, he can hear sounds from the past.  It never gets really steady enough to reach through.  They try pushing tools through the portal to pick up things in the past.  The steadier the portal, the easier it is to push tools through.  It never gets steady enough for them to push a tool all the way through, though.  It just gets easier to make progress.  One day, they have the portal open and it is acting really wild.  At some point the workers take a break.  The portal is still open, and while they are loafing the portal settles down by itself and becomes steadier than it has ever been.  So steady that a piece of the past falls through.  The portal scooped a chunk of the ground out of the past.  The chunk of ground contains a nest with dinosaur eggs.  The scientist  rescues the eggs, and they manage to keep them warm enough until they hatch.  The dinosaurs are some kind of harmless things, and become the lab mascots.  Always wandering the grounds, and in and out of the lab.  One day, the have the portal open again and one of the dinosaurs wanders into the lab and walks into some high voltage terminal.  Crash, bang.  Short circuit.  All the equipment to open the portal is destroyed, and the dinosaur is roasted from the flash.  The roasted dinosaur smells good, like chicken, and the scientist's son (who has been telling the story) takes a bite to see what it tastes like.  He says "It resembled chicken the way an asteroid resembles Jupiter."   It tastes fantastic. With all of their work ruined, and the ruins of a fortune in expensive equipment scattered around them, the scientists and the labworkers all chow down on dinosaur.  Half raw, half burned to a crisp from the explosion.  They eat the dinosaur down to the bones.  They start breeding the dinosaurs, and sell them as food.  The guy's father makes a fortune selling dinosaur meat, but remains unhappy.  With money from selling dinosaur meat, he rebuilt his lab but never ever got the portal steady enough to actually visit the past or take samples.  Does anyone know the name of the story and the author, and maybe what collection it might have been in? How can I remove malicious spyware, malware, adware, viruses, trojans or rootkits from my PC? $$\frac{1}{z-\sin z}$$ $$\frac{1}{z(1-\frac{\sin z}{z})}$$  the laurent's transform is also used to simplify the function.  the residue is found a $\frac{2*36*2}{5}$ but the actual answer is given as $\frac{3}{10}$ the residue is given as The solution is incorrect and also the pole is of the order 3. What does "bad girls go backstage" mean? (sorry for my poor English)  I saw this phrase somewhere but I don't know what this means..     Good girls go to heaven, bad girls go backstage   What means 'bad girls go backstage'?   Maybe.. it's when good girls try to be good, but bad girls become famous?  Am I right? I use (and have it much bigger) drive D: to store all my user data and games, but I have installed the Steam client on drive C:. When I was installing a first game (Warhammer 40000), I've chosen to place my library folder on drive D: and the game went there.  But now as I've got installed the second game (Portal), I can see that it was put on drive C: despite to the choice I've done previously. When I open Steam - Settings - Downloads + Cloud - Steam library folders, I can see both installation places in the list. Can I merge them into one?  I would even agree to use the default drive C: library (as I've replaced it with a symlink already). When I press to remove one library it says it can only remove empty ones. As of today I only knew about ubuntu-bug which I could use to report bugs about a specific program. But now I learned about apport-collect and apport-bug which basically are:  apport-bug - Reports problems to launchpad using Apport to collect a lot of information about your system to help the developers fix the problem and avoid unnecessary questions and answers.  apport-collect - Works as apport-bug but it send the information to an already existing bug report. In my case it was apport-collect 1060268 Thanks to Brad Figg in Launchpad.  Are there any other tools to report bugs? I accidentally removed my /etc/apt/sources.list file. Is it hosted by Canonical somewhere so I can re-add it to the system? It's a bit of an emergency, so I hope someone can provide a quick answer. Deleting another user's directories from my own I am a non-root user, and have made a directory into which other users in my group can write. The directory is setgid, so files and directories within it have the same group.  I can delete files placed into this directory, but if a user creates a subdirectory with files in it, I can't seem to delete those. Is there something special I can do (other than, say, bothering the user in question or the sysadmin about it) to get rid of this subdirectory?  EDIT: Inevitably, of course, someone asks "why?"  The shared folder in question is a mercurial repository. We can't use a shared-account ssh-key-based server for this like mercurial-server, and we can't just host it externally for various reasons. But that part works fine. We use Redmine for project management, but it does not yet read the repo index for file contents - it reads the working directory. So the working directory must be kept up-to-date. crontab has been disabled by the sysadmin, so that's out. So I naïvely put a changeset hook in the shared repo that performed an "hg update". This seemed to work fine initially, until, of course, someone pushed a commit with a new directory. While I had vague thoughts of trying to make a setuid script for the hook, I'll probably just consider safer avenues. Does walking fast prevent eggs hatching? I have a couple of eggs that I've picked up from some Pokestops (I'm lucky enough to live above one).   I walk a lot. I get to work through a 2 mile walk / train journey every day, so I should be picking up loads of steps for the eggs I have. However, because I'm normally always running late... for everything, I have to rush everywhere, so I walk at an above average pace.   Today I've walked around 5 miles, but the game has registered 100 metres. Is this because I walk too fast, or because of something else?  It's worth pointing out that I have the app open when walking... mostly because I have to catch them all. (This made me miss a train this morning... luckily I was early :D)