Class Property Containing a Global Variable
PHP class: Global variable as property in class
Why do shell script comparisons often use x$VAR = xyes? I see this often in the build scripts of projects that use autotools (autoconf, automake).  When somebody wants to check the value of a shell variable, they frequently use this idiom:  if test "x$SHELL_VAR" = "xyes"; then ...   What is the advantage to this over simply checking the value like this:  if test $SHELL_VAR = "yes"; then ...   I figure there must be some reason that I see this so often, but I can't figure out what it is. How do I uninstall Windows 8 and install Windows 7? I have a friend, who just got a new Toshiba Satellite C series with Windows 8. I tried to uninstall Windows 8 and install Windows 7 but was unable to do so.  I did everything I could:   Boot disk - would not load (error message Media -- Fail) Boot USB - would not load (error message Media -- Fail) Loading Windows 7 disk from system, fails with different errors   Does anybody know what I can do in order to install Windows 7? If $p$ is congruent to $2 \pmod 3$, how can I prove that all $a$, $1 \le a \le p-1$ are cubic residues $\mod p$? If $p$ is congruent to $2 \pmod 3$, how can I prove that all $a$, $1 \le a \le p-1$ are cubic residues $\mod p$?  Here's what I've done:  $1^3$ congruent to $1 \pmod p$ thus, 1 is a cubic residue, Also $(p-1)^3=(p-1) \pmod p$ implies  $$(p-1)^3 - (p-1) = (p-1)[(p-1)^2 -1] = (p-1)(p^2 -2p) = p(p-1)(p-2) $$ implies $$p|(p-1)^3 -(p-1)$$ Thus  $p-1$ is a cubic residue $\mod p$. Now I don't know how to show for $1\lt a \lt p-1$ are all cubic residues when $p$ is congruent to $2\pmod 3$. Can I rename the wp-admin folder? Is it possible to rename the wp-admin folder?  I know I could just rename it, but unless it's supported by the code lots of things would break.  If I use a custom folder name, it will make it slightly more secure, security by obscurity and all that. How to migrate MongoDB 2.4.14 file to MongoDB 3.6? I have a database file from MongoDB 2.4 and we want use this on mongodb 3.6.  note: the file is original from the db path. Not from mongodump. This process is messy as it requires doing so on many of our clients.  Any advice will be welcomed as I'm a bit lost in this process.  Thanks The first and (the) second chapter(s) are difficult - which is correct? I'm a little confused about the following sentences. Could you please tell me which one(s) is/are correct?        The first and the second chapter are difficult.   The first and the second chapters are difficult.   The first and second chapters are difficult.   The first and second chapter are difficult.      I believe #1 &amp; #3 are correct, while #2 &amp; #4 are incorrect.  But when seeing the answers to the Quora question , I wonder why they say #2 is correct. How to mount a virtual hard disk? Is it possible to mount a virtual hard disk (VHD, HDD, VDI, VMDK) on Ubuntu? How can this be done? Show the title character limit when writing a title I just ran into this while writing .  [I originally wrote:     you need a minimum of X reputation to comment on questions that are not your own, and on answers that are not to your own questions   But had to shorten it to:     you need a minimum of X reputation to comment]   First, it didn't tell me that I'd gone over the character limit for the title until after I had already tabbed out of the title field.  Second, it didn't tell me how much I'd gone over or anything. I had to copy-paste the text I'd written into my text editor in order to get some real-time feedback on the exact character count, to help figure out how to best shorten it. I'm trying to show that  $$\delta\big(f(x)\big) = \sum_{i}\frac{\delta(x-a_{i})}{\left|{\frac{df}{dx}(a_{i})}\right|}$$  Where $a_{i}$ are the roots of the function $f(x)$. I've tried to proceed by using a dummy function $g(x)$ and carrying out:  $$\int_{-\infty}^{\infty}dx\,\delta\big(f(x)\big)g(x)$$  Then making the coordinate substitution $u$ = $f(x)$ and integrating over $u$. This seems to be on the right track, but I'm unsure where the absolute value comes in in the denominator, and also why it becomes a sum.  $$\int_{-\infty}^{\infty}\frac{du}{\frac{df}{dx}}\delta(u)g\big(f^{-1}(u)\big) = \frac{g\big(f^{-1}(0)\big)}{\frac{df}{dx}\big(f^{-1}(0)\big)}$$  Can any one shed some light? Wikipedia just states the formula and doesn't actually show where it comes from. Proving that $\arctan(x)+\arctan(1/x)=\pm \pi/2$, could this line of reasoning possibly be correct? A question of Euclidean domain How do I overload the square-bracket operator in C#? DataGridView, for example, lets you do this:  DataGridView dgv = ...; DataGridViewCell cell = dgv[1,5];   but for the life of me I can't find the documentation on the index/square-bracket operator.  What do they call it?  Where is it implemented?  Can it throw?  How can I do the same thing in my own classes?  ETA: Thanks for all the quick answers.  Briefly: the relevant documentation is under the "Item" property; the way to overload is by declaring a property like public object this[int x, int y]{ get{...}; set{...} }; the indexer for DataGridView does not throw, at least according to the documentation.  It doesn't mention what happens if you supply invalid coordinates.  ETA Again: OK, even though the documentation makes no mention of it (naughty Microsoft!), it turns out that the indexer for DataGridView will in fact throw an ArgumentOutOfRangeException if you supply it with invalid coordinates.  Fair warning. I need to write an article with APA citations. I have sample code that works fine with style=authoryear, but if I switch to style=apa I get the following error message:   Error Line 21 ! Undefined control sequence.&lt;argument&gt; \printdateextralabel   I'm using TexMaker with biber. I've gone through example after example and I can't figure out what's wrong. I suspected it was with TexMaker or MiKTeX, but I just uninstalled and reinstalled both programs and I'm having the same issue. The same error message always pops up with the line number after \printbibliography. I tried copying corrected MWE's from other questions (such as  answered by Alan Munn) and I get the same error.  I included a MWE and my .bib file (borrowed from another thread) below.  File MWE:  \documentclass[article,12pt,letterpaper]{apa6} \usepackage[american]{babel} \usepackage{csquotes} \usepackage[style=apa,natbib=true,backend=biber]{biblatex} \DeclareLanguageMapping{american}{american-apa}   \title{Annotated Bibliography 1} \author{Joe Smith} \affiliation{Spectacular University} \addbibresource{bib.bib}  \begin{document} \abstract{abstract goes here} \maketitle this is a test \cite{Kim1999188} \printbibliography \end{document}   bib:  @article{Kim1999188, title = "Absorption of water vapour into lithium bromide-based solutions with additives using a simple stagnant pool absorber ", journal = "International Journal of Refrigeration ", volume = "22", number = "3", pages = "188 - 193", year = "1999", note = "", issn = "0140-7007", doi = "10.1016/S0140-7007(98)00061-9", url = "http://www.sciencedirect.com/science/article/pii/S0140700798000619", author = "Jin-Soo Kim and Huen Lee and Sun Il Yu", keywords = "Absorption", keywords = "Water", keywords = "Lithium bromide", keywords = "Absorption", keywords = "Eau", keywords = "Bromure de lithium " }      Here is a link to my . "Same as I do" or "same as I have" She has the same book as I have.  Isn't it supposed to be She has the same book as I do?  But I often hear the former.  Why? Is there any way to prevent mc from taking 10-30 seconds to open? Show timestamp of a vote in the tooltip when mousing over it Sometimes I come across an old question or answer that I voted on in the past, but I don't clearly remember when (or sometimes even why) I voted it up or down. Being able to see the date/time that I cast a vote would help me remember my mindset at the time.   When mousing over the toggled vote, the tooltip reads the same as if I hadn't voted, with no further information. For example:     This answer is useful (click again to undo)   The only way to get the timestamp is if I try to click the vote to undo it and get the locked vote message:     You last voted on this answer [datetime] Your vote is now locked in unless this answer is edited   However this requires me to guess that the vote is locked - if there was an edit since then I'll actually undo the vote and erase the info I was looking for.  Feature request: Please add the vote timestamp to the tooltip when mousing over a cast vote. This is already done with the green acceptance checkmark for example. Disallow closing of questions with a certain number of question / answer upvotes With reference to this currently open question   At the time of writing, it has 3 close votes yet has 7 question upvotes and the single answerer (11 upvotes) will have been awarded the enlightened badge (silver).  Therefore in the opinion of many (i) the question adds value and (ii) the answer adds value.  As a staring point for discussion, I suggest that 5 net question upvotes (and perhaps 5 answer net upvotes) should be enough to keep a question permanently open. Let's haggle over the numbers though. Thoughts? I am trying to build a custom Adventure Island. At this moment I am trying to limit the allowed items on this island. I'm trying to do this by filtering on a certain enchantment which is not item-specific.  For example.   When you want to filter an wooden sword with a custom name, you use this command:  /testfor @p[r=5] {Inventory:[{tag:{display:{Name:"Custom Sword"}}}]} &lt;   When you want to filter a wooden sword with a custom name and specific enchantement, you can use:  /testfor @p[r=5] {Inventory:[{tag:{display:{Name:"Custom Sword"},ench:[{id:16,lvl:1}]}}]} &lt;   But how can I filter on items with a specific enchantment on ANY item? I tried:  /testfor @p[r=5] {Inventory:[{tag:{ench:[{id:16,lvl:1}]}}]} &lt;   But this ain't work. Does anyone know how to solve this issue? Substr(). Add characters for each n digits Some people have a diamond after their username (e.g. )    What special privileges do diamond moderators have? How can I become a diamond moderator? Who are the diamond moderators?  How many are there?      For more information, see  in the .     Note: not to confuse with certain Stack Exchange employees, for example  members or "community managers", who often have diamonds as well, but are not ordinary moderators.