I am asking this question simply out of curiosity. Why the double differentiation is denoted by $\frac{d^{2}f(x)}{dx^2}$ and not by $\frac{d^{2}f(x)}{d^2x}$ or $\frac{d^{2}f(x)}{(dx)^2}$. Is there any mathematical reasoning behind it? It seems like a similar question has been asked before . But then the same discussion happened there, i.e., why $\frac{d^{2}f(x)}{(dx)^2}$ is not the correct notation :/
In Leibniz notation, the 2nd derivative is written as $$\dfrac{\mathrm d^2y}{\mathrm dx^2}\ ?$$  Why is the location of the $2$ in different places in the $\mathrm dy/\mathrm dx$ terms?
When to use self references or composition? Is it worth getting a suspension seat post as a cheap alternative to full suspension bike? I'm planning a ride from Birmingham to London on the Grand Union Canal (UK), which will be quite bumpy for most of the 145 mile distance.  I have a front suspension bike and can't afford a new full suspension bike.  Do suspension seat posts actually work?  If so, I'll get one of them.  Can anyone recommend a good model? On  we try really hard to fix spelling, grammar, and capitalization mistakes in question titles in order to avoid the . But occasionally someone enters a question with an all-lowercase title ().  It would be useful if the system could nudge the user toward capitalizing titles property by showing a hint when the user appears to be capitalizing incorrectly. For instance:    As  and  note in comments, the feature should also try to detect and advise against Title Case and ALL CAPS. Benchmarking hosting providers IO with Bonnie How to create a Customized Ubuntu Server ISO? What was Natsume hiding in her closet in episode 11? In episode 11 of Tokyo Ravens, what was Natsume hiding in her closet? When did the 5-foot square/hex become the standard unit of measurement in Dungeons & Dragons? I noticed that Synonymizer is only a bronze badge. Yet in order to obtain this badge you need to have 2500 reputation or more to even create tag synonyms. Then, on top of that you also need to be able to find a tag synonym.  Only 514 of these have been awarded... This makes the BRONZE badge Synonymizer rarer to have than most the gold medal badges. So my question is, why is this a bronze badge? Travelling to India via Germany with 2 stops, do i need transit visa? I have Indian passport and USA H1 valid visa, will be travelling US and my itinerary is Mumbai – Munich – Frankfurt – San Francisco. This route has two stops in Germany, Munich – Frankfurt is German domestic flight. I am not sure if I would need a Schengen or Transit Visa. I was going through few German and Indian consulate visa website but I am not able to get the correct info, specially below two statements are confusing. Could you please help me with this?    In these five airports in Germany you can stay at the International Transit Area without a visa: 1.  Cologne/Bonn 2.  Düsseldorf 3.  Frankfurt/Main 4.  Hamburg  5.  Munich  Airport transit privilege does not apply in the following cases and you will need to get a visitor visa if: You are transiting through two or more airports in the Schengen Countries Clarify an idiom in a political text Please carefully read the text below:     On 24 November, 1993, a meeting of Leftist intellectuals occurred in   London under the auspices of the Institute for Public Policy   Research (IPPR), which is a Labour-leaning think-tank.  A short document   was circulated in advance of the said meeting to clarify its   purpose.        Among other things, the document declared that the task of the   IPPR was: "To do what the Right did in the seventies, namely to break   through the prevailing parameters of debate and offer a new   perspective on contemporary British politics."    The explanatory document also said, "Our concern is not to engage in a   philosophical debate about foundations of socialism."      If this meant that those foundations were not the appropriate thing to   talk about at the 24 November meeting, then that might have been   right; not every thing has to be discussed at every meeting.  But if   what was meant was that discussion of philosophical foundations is not   what the Left now needs, then I disagree, and if that indeed is what   was meant, then it is curious that the breakthrough by the Right should   have been invoked as an achievement for the left to emulate, for if   there is a lesson for the Left in the Right's breakthrough, it is that   the Left must repossess itself of its traditional foundations on   pain of continuing along its present, politically feeble, reactive   course.  If the Left turns its back on its foundations, it will be   unable to make statements that are truly its own.   Since I've heard only one definition of the part identified in bold, I am at a dead end.  As you know, and according to Oxford's dictionary, the verb "repossess" means: To take back property or goods from SB who has arranged to buy them and can not pay.  Here, the object of verb is a thing not a person, but in the text, first,itself comes before of and its traditional foundations. As a result, I thought that this phrase might be an idiom and so has a different meaning with the original verb.  Please explain the meaning of this phrase. What are good advanced LaTeX books? I've been using LaTeX for about 3 months, and I'm hooked. My background is programming, so for the basic, google is sufficient. I did some research on amazon.com and found these two books with many positive feedback:    However, most of people said they are more like references than a real book. And if they really are, then I think I'd rather look up at CTAN. What I'm looking for is a book that can teach me how to program in LaTeX, for example:   Write my own package   Create animation  Create and using macro in LaTeX ....   I know there are many options around, however to pick the right one is not an easy task. Any advice or suggestion would be greatly appreciated. Thank you. I've found a couple of references () that suggest using final as much as possible and I'm wondering how important that is. This is mainly in the the context of method parameters and local variables, not final methods or classes. For constants, it makes obvious sense.  On one hand, the compiler can make some optimizations and it makes the programmer's intent clearer. On the other hand, it adds verbosity and the optimizations may be trivial.  Is it something I should make an effort to remember? Following are other questions which I think I need to know:   From a non X Session? (meaning root isn't logged into X) If multiple people were logged in on X, could I auto-detect who was on which screen, and thus programmatically detect which screen I need to launch the app on? Can I launch the app as the user? ( ok I'm 99.999% sure this is a yes ) Can I detect if users of group X are logged in to X? How to clear the interpreter console? Like most Python developers, I typically keep a console window open with the Python interpreter running to test commands, dir() stuff, help() stuff, etc.  Like any console, after a while the visible backlog of past commands and prints gets to be cluttered, and sometimes confusing when re-running the same command several times.  I'm wondering if, and how, to clear the Python interpreter console.  I've heard about doing a system call and either calling cls on Windows or clear on Linux, but I was hoping there was something I could command the interpreter itself to do.  Note: I'm running on Windows, so Ctrl+L doesn't work. Standard graded algebra How can I encode and decode percent-encoded strings on the command line? SharePoint 2013 Online - Missing Follow Link Installing mysql-workbench in Ubuntu 19.04 The error looks like this:  Reading package lists... Done Building dependency tree        Reading state information... Done Package mysql-workbench is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source E: Package 'mysql-workbench' has no installation candidate   How do I install it? Permission denied, are you root? I get this error whenever I try to install programs using the terminal:  home@ubuntu:~$ apt-get install myunity E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?   Also I'm unable to install updates using the terminal. apt-get update, unlinking