How do I make Firefox 7 remember my history shorter/longer?
How to Set Firefox 4 to only store History for a set period of time, i.e. one day?
I read this story in the early 2000s, but it was a Chinese translation so the English version could be older.  The beginning is a bit like the Passengers movie: on a spaceship, a man woke up from stasis too early and found that he could not go back to sleep. So he has to spend his whole life on the spaceship, alone.  For some reason (technical or ethical), instead of waking other people up, he created a fantasy adventure story featuring a brave prince as a pastime. He did stories, and drawings all over the inside of the ship. Then he died, not knowing how people are going to respond to his work. JSF 2.1 ViewScopedBean @PreDestroy method is not called $$f(x,y) = \left\{\begin{array}{cc} \frac{xy}{x^2+y^2} &amp; (x,y)\neq(0,0) \\ f(x,y) = 0 &amp; (x,y)=(0,0) \end{array}\right.$$  In order to verify if this function is differentiable, I tried to prove it by the theorem that says that if $\frac{∂f}{∂x}$ and $\frac{∂f}{∂y}$ exist and are continuous at the point $(x_0,y_0)$, then the function is differentiable at this point. So I did:  $$\frac{\partial f}{\partial x}(0,0) = \lim_{h\to 0}\frac{f(0+h,0)-f(0,0)}{h} = 0$$ $$\frac{\partial f}{\partial y}(0,0) = \lim_{h\to 0}\frac{f(0,0+h)-f(0,0)}{h} = 0$$  so we have that the partial derivatives at point $(0,0)$ is $0$. Now, if we take the derivative at $(x,y)\neq (0,0)$ and then take the limit of it as $(x,y)\to(0,0)$, we can see if the derivatives are continuous or not. So here it is:  $$\frac{\partial f}{\partial x}(x,y) = \frac{y(y^2-x^2)}{(x^2+y^2)}$$  but   $$\lim_{(x,y)\to(0,0)} \frac{y(y^2-x^2)}{(x^2+y^2)} $$ does not exist (by wolfram alpha... but can anybody tell me an easy way to prove this limit does not exist? easier than taking the limit in different directions?), therefore the derivative is not continuous at $(0,0)$, so we can't say $f$ is differentiable at $(0,0)$, but for $(x,y)\neq (0,0)$ the function is continuous, as it is a quotient of continuous functions. So $f$ is at least differentiable at $(x,y)\neq (0,0)$.   Now, to verify differentiability at $(0,0)$ I think we must use the limit definition of differentiablity: A function is differentiable at $(0,0)$ iff: $$\lim_{(h,k)\to (0,0)} \frac{f(0+h,0+k)-f(0,0)-\frac{\partial f}{\partial x}(0,0)-\frac{\partial f}{\partial y}(0,0)}{\|(h,k)\|} = 0$$  Let's calculate this limit:  $$\lim_{(h,k)\to (0,0)} \frac{f(0+h,0+k)-f(0,0)-\frac{\partial f}{\partial x}(0,0)-\frac{\partial f}{\partial y}(0,0)}{\|(h,k)\|} = \\ \lim_{(h,k)\to (0,0)} \frac{\frac{hk}{h^2+k^2}}{\sqrt{h^2+k^2}} = \\ \lim_{(h,k)\to (0,0)} \frac{hk}{(h^2+k^2)\sqrt{h^2+k^2}}$$  which I think, it's a limit that does not exist, therefore the function isn't differentiable at $(0,0)$ Numerical phenomenon. Who can explain? I was doing some software engineering and wanted to have a thread do something in the background to basically just waste CPU time for a certain test.  While I could have done something really boring like for(i &lt; 10000000) { j = 2 * i }, I ended up having the program start with $1$, and then for a million steps choose a random real number $r$ in the interval $[0,R]$ (uniformly distributed) and multiply the result by $r$ at each step.   When $R = 2$, it converged to $0$. When $R = 3$, it exploded to infinity.    So of course, the question anyone with a modicum of curiosity would ask: for what $R$ do we have the transition. And then, I tried the first number between $2$ and $3$ that we would all think of, Euler's number $e$, and sure enough, this conjecture was right. Would love to see a proof of this.    Now when I should be working, I'm instead wondering about the behavior of this script.   Ironically, rather than wasting my CPUs time, I'm wasting my own time. But it's a beautiful phenomenon. I don't regret it. $\ddot\smile$ I have a Minecraft 1.8.1 vanilla server and would like to reward certain users. I would like to /give some users a 99999/99999 durability renamed Diamond Pickaxe (with all enchantments on it). How do I use commands to change/repair the durability of items? If possible, using only one command and use /give. A friend recently got her ID stolen while she was in the Netherlands. She will soon need to fly to her home country Italy, but she doesn't know what to do.  What can one do in such a situation? As far as I know, since it's Schengen, you don't need an ID card to go through borders. On the other hand, this is air travel, so they always require it for security reasons.   Can she show another document that proves her nationality? A copy of the ID card? Anything? What is the "last" data that get's backed up, when running pg_dump on a live server? I'm wondering: If I start doing a pg_dump of a very large database (it would take hours), that is still running actively receiving writes, what is then the last data that goes into the backup? Is it:   The data as-it-was, at the point in time where the pg_dump command was initiated. The last changes that it encountered at some point where it was dumping that individual record. Something else.   Bonus question: If I'm trying to dump a database as part of trying to rescue it from corrupt data, will it then make any difference whether I use the directory format or the custom format? The title says it all. I want to resize windows with an right click while holding the alt key, instead of the new default alt+middle click.  I have found no way to enable this behaviour in 13.04. The gconf-Key suggested in this , doesn't seem to exist any longer. How to get GNOME Shell "Applications overview" to show the full name of applications How can I change the colors of lightning-button?  I tried doing this in my css:  .my-button {     background-color: #14a6bc;     color: #ffffff; }   and applying that class to my &lt;lightning-button&gt; and removing the variant but I still get the base colors? I am trying to use these examples: RC4 , Is it possible to find the key if we know the plaintext and ciphertext? Is it possible to find the key if we know the plaintext and ciphertext with RC4. How should I write the algorithm? Power Supply Capacity Formula Given that I am building a home computer from scratch and I have several components (MB, CPU, HDD, Video, Sound, etc) which have specific power requirements, is there a formula for me to calculate the size/capacity of the Power Supply I will need? I want to be able to expand the setup later on also... Can anyone recommend a good exposition of the theory behind partial least squares regression (available online) for someone who understands SVD and PCA?  I have looked at many sources online and have not found anything that had the right combination of rigor and accessibility.    I have looked into The Elements of Statistical Learning, which was suggested in a comment on a question asked on Cross Validated, , but I don't think that this reference does the topic justice (it's too brief to do so, and doesn't provide much theory on the subject).  From what I've read, PLS exploits linear combinations of the predictor variables, $z_i=X \varphi_i$ that maximize the covariance $ y^Tz_i $ subject to the constraints $\|\varphi_i\|=1$ and $z_i^Tz_j=0$ if $i \neq j$, where the $\varphi_i$ are chosen iteratively, in the order in which they maximize the covariance.  But even after all I've read, I'm still uncertain whether that is true, and if so, how the method is executed. Cannot connect MacBook Pro (Retina, 15-inch, Mid 2015) (10.13.3) to the internet through my Apple USB Ethernet Adapter. I am receiving this error under System Preferences/Network:   "Apple USB Ethernet Adapter has a self-assigned IP address and will not be able to connect to the Internet." IP Address: 169.254.59.248 Subnet Mask: 255.255.0.0   I can connect to the internet with the same ethernet port on my Windows 10 machine. When I replace the IP address with a the Wi-Fi IP address I use to successfully connect to the same network under "Using DHCP with manual address", the Apple USB Ethernet Adapter icon is green and displays the message "Apple USB Ethernet Adapter is currently active and has the IP address xx.xx.xx.252." However there is no actual internet connection (i.e., I cannot visit any website).  According to  to a similar problem, I can:   Find and disable whatever firewall is intercepting the DHCP return traffic. According to System Preferences/Security &amp; Privacy/Firewall, my firewall is off. Is there anywhere else I can check for additional firewalls? Would firewalls somehow impact ethernet and Wi-fi differently?  Inspect the network traffic or the router logs to see if and why the Mac DHCP broadcast packet is being ignored. How do I check network traffic on my Mac? I am comfortable using the terminal.   I have also tried steps listed as potential solutions in :   To reset the firewall, go to the /Macintosh HD/Library/Preferences/ folder and remove the file called "com.apple.alf.plist," and then restart your computer. On my computer I went to /Library/Preferences/ and ran sudo rm com.apple.alf.plist If that was already set, try the "Advanced" button, then "Renew DHCP Lease" Removing their "Ethernet" config from the Network settings and then re-adding   Does anyone have other suggestions? Thanks in advance Syntax to add multiple commands to a single command block I am looking to try and set multiple commands in a single command block, but so far everything I have tried just returns "Unknown Command".  What is the format for writing multiple commands in a single command block in Minecraft 1.8?  Can I use either of the following:  Command:(command here) Command:(command here)     /command here; /command here;   Or is there another format? Is it possible to split micro USB to USB cable so two cables (data + and data -) go to the PC with USB and two other power cables go to power brick? How can I invert a 'clip' selection within TikZ? I wish to draw an arc for a reflex angle on the outside of a triangle with coordinates (A), (B) and (C).  If I wanted to draw the arc inside the triangle I could use something like  \begin{scope} \path[clip] (A) -- (B) -- (C) -- cycle; \draw (B) circle (2mm);    % this is the little angle marker \end{scope}   Is there a straightforward way to exclude the part of the circle that's in the triangle, as in the pseudo-code below?  \begin{scope} \path[magicalinverseclipcommand] (A) -- (B) -- (C) -- cycle; \draw (B) circle (2mm);    % this is the little angle marker \end{scope}   EDIT: Although I included the code above as a motivating example of what an inverse clip would do, I would prefer a general solution that works systematically with any closed path, and not just in the particular example of a triangle with a circle clipped out of it. Looking at my question, I realise this isn't clear, and I will be happy with the best solution to my particular problem, but wonder if there is a less ad hoc solution than those listed so far. I have a raster image (Sentinel-2 band 4) and a shapefile covering the same area than the image (same projection and extension). The shapefile has different polygons which are agricultural fields.   I want to create a new file where, for each polygon, the mean value of the pixels that are inside it is calculated.  Could you please help me to find an appropriate R code for that? I used the upgrade manager to upgrade from 17.04 to 17.10. When I start the machine, I only get a black flickering screen now. I was using the nvidia binary drivers before the upgrade.     NOTE: This question (and answer) relate to a specific issue when upgrading from 17.04 to 17.10 while using Nvidia or AMD binary drivers. You might experience a completely different issue. For that please see the more general question . Was voldemort's body going to die? Voldemort has gained "immortality" via his horcruxes, but was his body immortal to age? Looking at all the questions about Voldemort and his horcruxes what was his plan to keep his body alive. We know his first Horcux was created at age 16, yet we see him age still so it seems like eventually his body would die of old age and his soul would be left in the half dead state he was in after his spell rebounded off Harry. What was his plan here, why would he not want something such as the elixir of life to keep his vitality?     While the Elixir of Life does indeed extend life, it must be drunk regularly, for all eternity, if the drinker is to maintain his immortality. Therefore, Voldemort would be entirely dependent on the Elixir, and if it ran out, or was contaminated, or if the Stone was stolen, he would die just like any other man. Thereafter, I am convinced, he intended to continue to rely on his Horcruxes: he would need nothing more, if only he could regain a human form. He was already immortal, you see ... or as close to immortal as any man can be.' (Albus Dumbledore)   Horcruxes seem to fail at something important, keeping you alive, they stop you from dying truly yes, but they don't keep you alive. Harry is shown over and over again to be able to beat better wizards because hes has faster reflexes both because of youth and his genetics, but presumably by 50 harry will not be as fast as his 16 year old self even considering their longer life expectancy. Why operate in a body of a 50 year old?