Compiling this code  \documentclass[a4paper,12pt,twoside]{article} \usepackage[utf8]{inputenc} \usepackage[T1]{fontenc} \usepackage[ngerman,english]{babel}  %MATHEMATICS \usepackage{mathbbol} \usepackage{amssymb} \usepackage{amsmath} \usepackage{amsthm}  \usepackage{tikz-cd}  \begin{document} \begin{center} \begin{tikzcd}[column sep=huge] F(X)   \arrow[r,"F(X)"]\arrow[d,"F(X)"]&amp;F(X)\arrow[d,"F(X)"]\\ F(X)\arrow[r,"X^{{\mathcal D}}_{F(X),F(Y)}"]&amp;F(X) \end{tikzcd} \end{center} \end{document}   I got the error 'Undefined controll sequence \end{tikzcd}'. And the reuslt looks not good at all. How can I fix that problem?
Sorry for the bad English. I'm trying to use the tikz-cd package to make commutative diagrams. My code  \documentclass{article} \usepackage[brazil]{babel} \usepackage{tikz-cd} \begin{document} \begin{tikzcd} A \ar[r, "x"] &amp; B \end{tikzcd} \end{document}    The problem occurs when putting a name under the arrow, the syntax "x" is incompatible with the brazil option of the babel package. When exchanging brazil for english it works normally. I already tried using  \usepackage[main=brazil, english]{babel}, \usepackage[brazil, english]{babel} e  \usepackage[brazil, main=english]{babel}   But it did not work. I also tried to use  \usepackage[english, brazil]{babel} \usepackage{polyglossia} \setmainlanguage{brazil} \setotherlanguages{english}   And finally  \selectlanguage{english}   However, it only works if I remove the option brazil
I'm using post thumbnails to link to a page.  Is it possible to add a class name to the post thumbnail image.  &lt;li&gt;&lt;a href="&lt;?php the_permalink(); ?&gt;" &gt;&lt;?php the_post_thumbnail(); ?&gt;&lt;/a&gt;&lt;/li&gt; Oracle: how to UPSERT (update or insert into a table?) The UPSERT operation either updates or inserts a row in a table, depending if the table already has a row that matches the data:  if table t has a row exists that has key X:     update t set mystuff... where mykey=X else     insert into t mystuff...   Since Oracle doesn't have a specific UPSERT statement, what's the best way to do this? Russian SE has a slightly longer and more storied history than Japanese SO Short story about astronauts landing on a planet of shapeshifters I'm trying to find an English-language short story I read in a collection about five to ten years ago (I don't have any idea of the original publication date).    Here's everything I remember:   The story is about human astronauts landing on an alien's planet, from the alien's point of view. Every organism on the alien planet is part of a single hive mind, and they can telepathically infect the humans (the aliens view this as beneficial, as any mind separated from the hive must be suffering), but choose not to once they realize that there's an entire planet of humans out there. The narrator alien is an organism that was designed by the hive to mimic a non-essential component on the spacecraft, so it can stow away when the humans return to Earth. The narrator alien is preparing to infect all of Earth as soon as the shuttle's door opens, but the component it replaced was the wire that opens the door, so it is fried instantly by the current.   Despite knowing all these elements of the story, I haven't had luck Googling it, because so many of these elements are very common sci-fi themes on their own, and I don't remember any unique names/terms.  I don't remember if I read this in a Sci-fi anthology book, or in a magazine (like 'Asimov').  Thanks in advance if anyone can help me track this one down, it's been bugging me for a long while. How can I check for an empty/undefined/null string in JavaScript? I saw , but I didn't see a JavaScript specific example. Is there a simple string.Empty available in JavaScript, or is it just a case of checking for ""? Fibonacci Recurrence Relations Solve the recurrence relation $f(n) = f(n − 1) + f(n − 2)$ with initial conditions $f(0)=1$, $f(1)=2.$   So I understand that it grows exponentially so $f(n) = r^n$ for some fixed $r$.  This means substituting this $r^n = r^n-1 + r^n-2$ which gives the characteristic equation of $r ^ 2 - r - 1 = 0$. I'm not 100% sure where to move on from here. Solving $x^p + y^p = p^z$ in positive integers $x,y,z$ and a prime $p$ The question is from Zeitz's ''The Art and Craft of Problem Solving:"      Find all positive integer solutions $x,y,z,p$, with $p$ a prime, of the equation $x^p + y^p = p^z$.   One thing I noticed is that   $$ \frac{x^p + y^p}{x + y} = \sum_{i=0}^{p-1}x^{(p-1)-i}(-y)^i \implies (x+y) |p^z \implies x + y = p^n, \text{ }n &lt; z   $$  It is also not hard to determine all solutions for $p =2$. After this, however, I am at a loss. I don't know what restrictions I can impose to try to narrow down the solution set; for example, the class of solutions  $$ p=3, x = 3^n, y = 2\cdot3^n, z = 2 + 3n $$  for $n \ge 0$ show that $x+y = p^n$ cannot be sharpened. (Let me note that these are the only other solutions I have found besides the ones for $p = 2$.)  Could anybody give me a push in the right direction on this problem? How to disable notifications for a single mailbox in Mail? When managing multiple mailboxes, is it possible to disable the notifications for certain mailboxes? I understand that you have to have visas to enter some countries, but I was wondering whether you have to pay for each visa separately or you can get a visa to go everywhere. You see videos and lists on what you should pack to travel the world, but no lists on the documentation needed. How do we perform transverse measurements in a two level system? In quantum mechanics any two level system can be mapped onto effective spin variables. If the system is defined by two energy levels, $|E_1\rangle$ and $|E_2\rangle$, the Hamiltonian is  $$ H = \left(\begin{array}{cc} E_1 &amp; 0 \\ 0 &amp; E_2 \end{array}\right) \, .$$  This can be recast as  $$ H = \frac{E_1+E_2}{2} 1\!\!1 + \frac{E_1-E_2}{2} \sigma_3\, .$$  $1\!\!1$ is the identity operator and $\sigma_3$ is the third pauli matrix. This is very nice because we can now apply our knowledge and intuition of spin dynamics to any two level system.  My question is the following: for a real spin I can measure expectation values of $\sigma_{1,2}$ by physically rotating my system and align its $x$ or $y$ axis with my measuring apparatus. How do I do this (in the lab!) with a pseudo-spin system? Imagine I am looking at a cold atom and I want to know if the system is in an symmetric or anti-symmetric superposition of $|E_1\rangle$ and $|E_2\rangle$, how do I do it? How to edit a file in vi editor (arrow keys prints letters)? I am open a file in vi:  vi index.php   Here the problem is: when I press the down arrow and it prints 'B'. Why it prints 'B'? which novel involved sending instantaneous tachyon body copies around the galaxy, mostly to die? The novel centers around a man living a comfortable existence in the pretty distant future.  To support himself, he is occasionally asked to enter a box which will copy his entire body, and send it out faster than the speed of light to some developing world, to work.  His copy on this world wakes up and realizes what a big mistake he's made.  The copy does grueling work, feels lonely, and eventually just dies of radiation sickness.  Back on earth, the man never realizes how bad it is out there, and keeps sending out more copies.  I think the story is probably 80s or earlier - not sure if it's a short story, or the beginning of a novel which I lost &amp; never finished. Does iOS have a firewall? Where is it preferred to place the answer to duplicate questions? Is it possible for an x86 processor to match an ARM processor in terms of performance per watt? From my personal experience with my tablet, and from the benchmarks and articles I've read, it always seems ARM processors, as seen in virtually all mobile devices, deliver incredible performance for the amount of power they consume.  It really seems like ARM is inherently more power-efficient than x86.  To me, it looks like that this is because x86 is a  while ARM is a . However, Intel Atom processors deliver very good performance relative to their power consumption as well.  In addition, having studied computer architecture, it is my understanding that in modern processors, the complex x86  is internally translated into simpler  that use an internal instruction set that is closer to the simpler ARM or MIPS ISAs than x86 proper.  As such, the ISA as presented to the programmer is little more than an interface to issue commands to the processor, rather than a representation of the actual low-level operations the chip performs.  Then again, implementing this translation layer requires additional silicon space on the chip...  That said, assuming that they are implemented using the same semiconductor process, is ARM inherently more efficient than x86? With a properly designed , is it possible for an x86 processor to deliver the same performance per watt as an ARM processor?  Remember, I'm looking for a well-written technical answer in the spirit of Stack Exchange and not mere speculation. Prove that the function : $f(x) = x$ when $x$ is rational and $f(x) = 1 - x$ when $x$ is irrational is continuous at $x = \frac{1}{2}$  To prove the continuity it is necessary to prove that for every $\epsilon$ there exists a $\delta$ such that $|f(x) - f(\frac{1}{2})| &lt; \epsilon$ whenever $|x -c| &lt; \delta$ $- (1)$ Now if we choose $a  € (\frac{1}{2} - \delta, \frac{1}{2} + \delta)$ and also $a $ is rational and choose $\epsilon &lt; |a - \frac{1}{2}|$ then condition in $(1)$ is not satisfied. How to move from here? What's a word for a positive kind of "envy" without the sense of resentment? Imagine your college buddy is now running a multi-billion dollar company, while you're still stuck at the same white-collar day job 5 years after graduation. You chat with him and want to express the idea that you're happy for him and fancy having his lifestyle--something like "I wish I could buy a yacht and cruise around the world like you do; I'm glad you're doing really well!"  Basically, it's the feeling of envy when you take out the resentment from it. Is there a word for it?   (I thought about "admire", but found it too strong and broad) I accidentally moved all folders from root to a subfolder. (/bin, /etc, /home, /lib, /usr... all moved) The only ones that were not moved, since they were in use, are  /bak, /boot, /dev, /proc, /sys.  Now, any command that I try to execute will simply not happen. I constantly get "No such file or directory".  I am connected through ssh and through ftp, but I cannot move files through ftp, as direct SU login is disabled. I also have access to the actual server if I need to do something directly from there.  I'm assuming I would need to edit a configuration file in order to tell it where to find the /bin folder and that would help me get access again, but I don't know which file that would be or how to do it (since I can't even run chmod to change permissions).  Is there any way out of this other than re-installing?  I am working on an old version of CentOS.  I'm extremely new to the world of Linux, hence this action and the question... Earlier today my 2009 iMac emitted I/O errors trying to copy files. So I ran disk utility, verify disk to see if anything was amiss. It was. But as it's my startup disk I couldn't repair it, so I tried safe mode. Safe mode worked the very first time, but when I rebooted it shows the progress bar filling up, before halting. Every time I turn it on now, the same progress bar then crash happens. Booting in verbose mode reveals fsck is failing with signal 8.  Using single-user mode, as that's as far as I'm aware the only way I can get any access to the system, I've been running fsck_hfs. However, it always fails. Below is the output from fsck_hfs -d /dev/disk0s2.  ** /dev/rdisk0s2         Using cacheBlockSize=32K cacheTotalBlock=65536 cacheSize=2097152K. ** Root file system    Executing fsck_hfs (version diskdev_cmds-491.6~3). ** Verifying volume when it is mounted with write access. ** Checking Journaled HFT Plus volume. ** Checking extents overflow file. ** Checking catalog file.    Missing thread record (id = 9931104)    Missing thread record (id = 16434146)    Missing thread record (id = 19370458) disk0s2: I/O error hfs_swap_BTNode: offsets 10 and 11 out of order (0x0000, 0x0000)    Invalid node structure (4, 115897) ** The volume Macintosh HD could not be verified completely.         volume check failed with error 7         volume type is pure HFS+         primary MDB is at block 0 0x00         alternate MDB is at block 0 0x00         primary VHB is at block 2 0x02         alternate VHB is at block 1952491198 0x74622d5e         sector size = 512 0x200         VolumeObject flags = 0x07         total sectors for volume = 1952591200 0x74622d60         total sectors for embedded volume = 0 0x00   I absolutely need to be able to boot to use it as an external monitor. How to create a permanent "alias"? If you create an alias for example:   alias cls="clear"   It exists untill you kill terminall session. When you start a new terminal window the alias doesn't exist any more. How to create "permanent" alias, one that exists in every terminal session?