I went to remove some tags from a question and normally I have enough rep to do this.  However, on this occasion, it appears that someone with not enough rep tried and instead I could approve an edit to do the same thing, but this wasn't enough.  In other words, I was prevented from removing tags by someone trying to do the same thing but not enough rep.  This struct me as a bit complicated.  If I can remove tags, perhaps I should be able to remove them even if someone with not enough rep has already tried to remove them.
Note that this is not the same as:   Mistagged questions should be retaggable immediately.
Does a photon exert a gravitational pull? Why should the substitution be injective when integrating by substitution? I made a silly mistake in evaluating some integral by using a non-injective $u$-substitution.  But why should $u$-substitutions be injective in the first place?  I reasoned in the following way: the formula $$ \int_{\phi(a)}^{\phi(b)}g(x)\ dx = \int_a^b g(\phi(t))\phi^\prime(t)\ dt $$ holds for a general $C^1$ function $\phi$, even if it is not injective.  When you calculate an integral of the form $\int_a^b f(\phi(t))\ dt$, to use the formula above from right to left, you should find a function $f$ such that $$ f(\phi(t)) = g(\phi(t))\phi^\prime(t), $$ which do not exist if $\phi$ is not injective, i.e., $\phi(t) = 0$ for some $t$. This is why substitutions should be injective.  Is my reasoning correct?  If so, I believe that if $\phi^\prime(t) = 0 \Rightarrow f(\phi(t)) = 0$, a function $g$ that satisfies the formula above may exist and $\phi$ should not necessarily be injective.  Is this right?  I am often confused about the fact $\phi$ should be injective.  Is there an intuitive way to interpret this fact, so that I always remember to take a $\phi$ that is injective?  I would be grateful if you could help me understand this matter. Typesetting annuity and life-insurance symbols in ConTeXt How do I typeset annuity and life-insurance symbols, actuarial notation in ConTeXt. I see there are packages available but not for ConTeXt.    Thanks I am really confused in Gauss law.  Why do E3 and E2 pointing up? and also E1 pointing down?  The lecture note said infer from symmetry and you will get the following but I dont really understand. Could anyone explain to me? I am new to gauss law. Superman has been exploited by Poison Ivy in Hush, and he's definitely mad in Injustice. What about Batman? Has Batman ever had to be brought to justice/stopped/killed by his fellow superheroes? (That one time when Superman dreams of Batman snapping Joker's neck doesn't count)  Edit: The Dark Knight Returns doesn't count: Batman wasn't really mad, and he wasn't wrong either. Suppose I have a function $f$ that is analytic on the unit disk $D = \{ z \in \mathbb{C} : |z| &lt; 1 \}$ that is also continuous up to $\bar{D}$. If $f$ is identically zero on some segment of of the boundary (e.g. $\{ e^{it}, 0 \leq t \leq \pi/2 \}$ ), is it then true that $f$ is identically zero on the entire boundary?   I know that analytic functions that are zero at an accumulation point inside the domain of analyticity are identically zero throughout the entire domain, but I don't know what (if anything) can be said if something similar occurs on the boundary of the domain. Hint:  $a^2 -ab +b^2 = (a+b)^2 -3ab.$  I know we can say that there exists an $x,y$ such that $ax + by = 1$.  So in this case, $(a+b)x + ((a+b)^2 -3ab)y =1.$  I thought setting $x = (a+b)$ and $y = -1$ would help but that gives me $3ab =1.$  Any suggestions? Why does sudo change the PATH? How to best encapsulate monetary values in a database Reflection to Identify Extension Methods Checkbox in listview control Can you have a multicolumn listview control where one of the columns is a checkbox?  Example code or links would be greatly appreciated.  I am using visual studio 2005 bash: syntax error near unexpected token `}' I tried using this:  $ if [$a == 1] then { echo 'yes'; } fi;   but I get an error:  -bash: syntax error near unexpected token `}'   What is the correct format?  I tried several with no luck. How to validate an email address using a regular expression? I have Ubuntu 16.04 LTS installed on my PC. I have a problem playing  videos on google chrome. Version of google chrome: 51.0.2704.63 (64-bit). All other videos of youtube are playing normally in google chrome. I even tried playing the  videos on Firefox but the same problem persists. Can anyone help me with the same ? As a physics student, I have occasionally run across the gamma function  $$\Gamma(n) \equiv \int_0^{\infty}t^{n-1}e^{-t} \textrm{d}t = (n-1)!$$  when we want to generalize the concept of a factorial.  Why not define the gamma function so that   $$\Gamma(n) = n!$$  instead?  I realize either definition is equally good, but if someone were going to ask me to choose one, I would choose the second option.  Are there some areas of mathematics where the accepted definition looks more natural?  Are there some formulas that work out more cleanly with the accepted definition? Where to put the escape characters? I've tried to change my prompt by editing .bashrc:  export PS1="\e[0;32m[\u@\h \W]\$ \e[m"   This seems to work, but ctrl-r to access reverse history ends up with my typing not appearing in the same place as it will be interpreted (like ). It is fine when using the up or down arrows to select previous commands though.  I've had a look at that question, but can't seem to work out where to apply the escape characters in my prompt. I've tried a few combinations but then I break normal text typing functionality or simple back/forwards through history.  If you could include an explanation of which instances of characters need escaping and why, that would help me (and hopefully others) learn. Prove that the equation $x^4+(2k^2)x^2+2k^4$ is not a perfect square Database synchronization between dev/staging and production I have a problem with WordPress database synchronization between development and production and I am wondering how other people solving it. I am aware about  but it doesn't really cover the nastier and more realistic use case.  Say I have a live WordPress website. I took a dump of everything, replicating it on our dev environment. I started making changes. 1 week later I am ready to deploy my updates. In the meantime, database on production site has changed(new posts, new comments, etc.). How do I synchronize changes between production and development during the rollout and is it possible to automate(somewhat at least) this process? Find images by size: find / file / awk I've been trying to find png image files a certain height (over 500px).  I know that file will return image dimensions.  Example:    $ file TestImg1a.png  TestImg1a.png: PNG image data, 764 x 200, 4-bit colormap, non-interlaced      But I need to use this to find all files in a directory with a height over 500px.  I know how to print out all files regardless of height:  find . -name '*.png' | xargs file | awk '{print $7 " " $1}'   But how do I limit the $7 to those results greater than 500? The bikeshed problem and Stack Exchange In short, :     If you go before the Board of   Directors and ask for 1.5 billion   dollars to build a nuclear reactor, no   one will review or discuss the details   of the plant. They will assume that   experts have been over every inch of   the plans, and not want to look   foolish by asking a silly question.      However, if you ask the same group to   approve a 30 dollar expenditure for   lumber with which to build a bikeshed   (presumably a British term for the   smallest possible building) then be   prepared for a 45 minute discussion   about all aspects of the bikeshed,   including the color of the paint. The   explanation for this is that everyone   can grasp the scale of a bikeshed.   To transform this problem to Stack Overflow terms, questions that are trivial such as "How to convert a C string to a QString or "What is the difference between . and ->" get a lot more views, answers and votes than real questions of the form "How do I frob this widget" that bother real professionals. Fewer views mean less possible votes for good answers and hence less incentive for people to answer.  How can Stack Exchange solve this problem?