I am trying to run a server that requires Java 7 using terminal.  After installing Java 7, typing java -version in terminal still shows Java 6.  Previously, I would use the Java Preferences application, but Apple has removed it.  Does anyone have any idea how to change the Java version the system uses without the Java Preferences application?  Or if anyone knows a download link for Java Preferences, that would be greatly appreciated as I am able to achieve the same results by just using that.  Thank you so much!  I am using the latest version of Mac OS X
I just installed Oracle's Java version 7u7 on my Mac (running OSX Mountain Lion). However, when I run java -version it still displays the old version (6u29).    How do I fix this? Do I even need to fix this? What version will browsers (Firefox) use in this case? And what version will be used when I run Java applications directly?  I've seen  but this doesn't work in my situation (probably because this question is about the JRE and the other question about the JDK). In my case the Java Preferences app only displays Java 6 versions (32 bit and 64 bit).    Update:   which java points to /usr/bin/java /usr/bin/java is a symlink to /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands/java /System/Library/Frameworks/JavaVM.framework/Versions/ only contains the folder A (awesome version name) - which Current points to.
Question is pretty much in the title: is it possible for an alliance to win as one, instead of a single player being the winner?  And if there is such way, is there a difference between classic and disharmony? iPhone Apps in Waiting mode for the last 4 days I tried to download the "Dictionary Free" app from the App Store four days ago, but it's been stuck in "Waiting" ever since. I've tried everything: rebooting the phone, restoring from an iTunes backup, side-loading the app from iTunes, but nothing has worked.  When I turn Airplane Mode on and then off again, I get an alert popup that says "Unable to download application. It will be available for download when you log in to the iTunes Store on your computer".  I've tried what it recommends, but nothing seems to work. I am kind of confused on the terminology of &quot;space&quot;. From  I am getting that  In mathematics, a space is a set (sometimes called a universe) with some added structure.  And from topological and metric spaces, I know that we a space is a a tuple of a set and a structure, e.g. $(X, \tau)$, $(X, d)$, where $\tau$ and $d$ are a topology and a metric respectively. On the other hand, in machine learning the term &quot;features space&quot; is used a lot for sets like $\mathbb R^n$, e.g.  and although it often refers to the set underlaying set itself, not the tuple of set plus the added structure. In fact, I have done the same in a previous publication (which the peer-reviewers accepted), but I would like to be both correct and precise in what I research, write, and submit. Is it just that machine learning researchers are imprecise in their terminology? Is it just an ? I think, what some people are doing, might be they consider a space to be a set, which is somewhat structured, instead considering the set with the structure (so, the tuple), to be the space.  I am not sure how to think about this. How do I deal with this in my writing? Especially since, what happens a lot is that I need subsets and element out of the underlying sets of all kinds of spaces.  Of course it would greatly help if there was a general name for a set that is the underlying set of a space, , but it seems that there is no dedicated name for such a set. Let's say there was a features space $(X, \cdot)$, (where I am not even sure, what structure we would add). Then it would be great to have a name for the set, let's call it an asdf. So we could say the feature asdf.  Afterthoughts: What makes it worse for me is that it seems ( and ) I am not even using the word &quot;structure&quot;, right, since it is about operations, so we are talking about an &quot;algebraic structure&quot;, while &quot;geometric space&quot; is... something else...? So apparently a &quot;vector space&quot; is actually not a &quot;geometric space&quot;, but an &quot;algebraic structure&quot;. I can understand that point, but the language gets even more confusing. How to correctly install libpng12-0 on the Ubuntu 19.10? For  I need to install libpng12-0 package on the Ubuntu 19.10 system.  I know that it is available .  So I have decided to download this package manually and install it by hand.  On previous Ubuntu versions (such as 18.04 LTS) this trick ends with success, but here on 19.10 it fails in very strange way:   wget http://mirrors.kernel.org/ubuntu/pool/main/libp/libpng/libpng12-0_1.2.54-1ubuntu1.1_amd64.deb sudo apt-get install ./libpng12-0_1.2.54-1ubuntu1.1_amd64.deb  0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded. Need to get 0 B/116 kB of archives. After this operation, 285 kB of additional disk space will be used. Get:1 /home/user/libpng12-0_1.2.54-1ubuntu1.1_amd64.deb libpng12-0 amd64 1.2.54-1ubuntu1.1 [116 kB] Selecting previously unselected package libpng12-0:amd64. (Reading database ... 212864 files and directories currently installed.) Preparing to unpack .../libpng12-0_1.2.54-1ubuntu1.1_amd64.deb ... Unpacking libpng12-0:amd64 (1.2.54-1ubuntu1.1) ...  dpkg: error processing archive /home/user/libpng12-0_1.2.54-1ubuntu1.1_amd64.deb (--unpack):  unable to install new version of '/lib/x86_64-linux-gnu/libpng12.so.0': No such file or directory No apport report written because the error message indicates an issue on the local system                                                                                          Errors were encountered while processing:  /home/user/libpng12-0_1.2.54-1ubuntu1.1_amd64.deb E: Sub-process /usr/bin/dpkg returned an error code (1)   What is wrong here? How can I get libpng12-0 installed on Ubuntu 19.10 system?    Note: the same happens on 19.04, but it is near EOL. When do I apply Significant figures in physics calculations? I'm a little confused as to when to use  for my physics class. For example, I'm asked to find the average speed of a race car that travels around a circular track with a radius of $500~\mathrm{m}$ in $50~\mathrm{s}$.  Would I need to apply the rules of significant figures to this step of the problem? $$ C = 2\pi (1000~\mathrm{m}) = 6283.19 $$  Or do I just need to apply significant figures at this step? $$ \text{Average speed} = \frac{6283.19~\mathrm{m}}{50~\mathrm{s}} = 125.664~\mathrm{m}/\mathrm{s} $$  Should I round $125.664~\mathrm{m}/\mathrm{s}$  to  $130~\mathrm{m}/\mathrm{s}$ since the number with the least amount of significant figures is two? How do I write this matrix as a product of elementary row matrices. \begin{pmatrix}3&amp;-1&amp;3\\ -2&amp;3&amp;2\\ 1&amp;-3&amp;1\end{pmatrix}  Any help would be greatly appreciated!  I have done this before with other matrices, yet this one is bringing me trouble. I have spent too long on this as I believe it should be easy and yet my answers are always wrong. What Do you do after you get the identity matrix?  What I am doing: So I first row reduce it to the identity matrix:   I first switch $R_1$ and $R_3$ Then $R_3-3R_1$ then $R_2+2R_1$ then $-1/3R_2$ then $R_3-8R_2$ then $R_2-2R_1$ then $3/32R_3$ then $R_1+3R_3$ and finally $R_2+4/3R_3$   I know there is many possible ways to get this too the identity matrix but this worked for me. I then apply all of the above steps to identity matrices and multiply them together to check my work but it never works out to be the original matrix so I am forced to believe something is wrong. Elliptical orbits of planets As we know, the velocity of the planet changes as it orbits around the sun, both in its magnitude and direction. The centripetal acceleration causes the change in the direction of velocity but I want to know what is the tangential force that acts on the planet to change the velocity by its $magnitude$. The answer normally as to why the speed changes is: If  the  force  that  the  Sun  exerts  on  the  planet increases  (as  the  planet moves closer),  then  the acceleration   of  the  planet must  increase,  resulting  in a  higher  orbital  speed,  and vice  versa. But this force is not along the body but towards the sun. So such a force should only change its direction. Can you determine a formula for this problem? Using crawl rules to exclude Allitems.aspx, DispForm.aspx Is anyone having any idea on how to exclude List Forms from Search result.  I tried lot many things suggested on google, but none of them seems to be working. I'd prefer as little formal definition as possible and simple mathematics. Problem with babel and tikz using \draw I'm trying the next code:  \documentclass[pdftex,spanish]{article} \usepackage{babel} \usepackage{tikz}  \begin{document}  Simple arrow:   \begin{tikzpicture}     \draw[-&gt;] (-1.5,0) -- (1.5,0); \end{tikzpicture}  \end{document}   but it doesn't work. It throws the errors:    ! Argument of \language@active@arg&gt; has an extra }. ! Paragraph ended before \language@active@arg&gt; was complete.&lt;to be read again&gt;\par \draw[-&gt;]   What can I do if it works right without the babel package? What does "calculus" mean? "calculus" and "formal system"  From      a calculus is a formal system that consists of          a set of syntactic expressions (well-formed formulæ or wffs),    a distinguished subset of these expressions (axioms), plus    a set of formal rules that define a specific binary relation on the space of expressions.      From      Formal systems in mathematics consist of the following elements:         A finite set of symbols (i.e. the alphabet), that can be used for constructing formulas (i.e. finite strings of symbols).   A grammar, which tells how well-formed formulas (abbreviated wff) are constructed out of the symbols in the alphabet. It is   usually   required that there be a decision procedure for deciding whether a   formula is well formed or not.   A set of axioms or axiom schemata: each axiom must be a wff.   A set of inference rules.      what is the difference between a formal system, and a calculus, then? I think they are the same? "calculus" and "logic system"  "Calculus" appears in "propositional calculus" and "first-order predicate calculus", which are also called "propositional logic" and "first-order logic" respectively. So I thought "calculus" and "logic" mean the same, and "a logic" is, according to ,      A logical system or, for short, logic, is a formal system together with a form of semantics, usually in the form of model-theoretic   interpretation, which assigns truth values to sentences of the   formal language, that is, formulae that contain no free variables.    But then I saw "calculus" also appears in "lambda calculus", which is also a formal system. I think a lambda calculus isn't a logic system, right? What does "calculus" mean in "lambda calculus"? Furthermore  "calculus" can also mean computational real analysis for first-year college students.   Thanks. Faithful representation of the Heisenberg group I have been trying to solve a problem concerning the Heisenberg Lie group $H$. Show that there does not exist a faithful representation $\rho:H\to\text{GL}(2,\mathbb{R})$.  Any ideas about how to solve it would be very appreciated. Lightsabers are not made of light, nor have they anything to do with lasers (even if there are people who mistakenly refer to them as "laser swords").   Blaster bolts are also not lasers. They travel significantly slower than light, they travel even slower than ordinary bullets fired by gunpowder. (called slug throwers on the Star Wars universe)  Was there any use of lasers ever presented in the Star Wars universe, either as we use them today, or as weapons?  By laser I mean something which behaves like laser does, even if it's not called by that name in a movie or book. If something is called a laser (in the script or by fans) but clearly doesn't work like a laser (for example, it travels slowly, and in visible blocks) it doesn't count. Tikzpicture-figure: Order plot data (asc/desc)? I am using a tikzpicture for plotting. the values I want to plot are typical (X,Y) pairs. The x-value is an uninteresting id-value. I want to order the bins ascending/descending according to the y-value, but how do I do that? The figure seems to automatically take the x-values for ordering, how can I override that? (I am not particularly fixed to tikzpicture - its just the first thing that actually worked and displayed the plot....) Following minimal-working example, how could I achieve a reordering according to the y-value?  \documentclass{article} \usepackage[english]{babel} \usepackage[T1]{fontenc} \usepackage[utf8]{inputenc} \usepackage{relsize} \usepackage{times} \usepackage{url} \usepackage{latexsym} \usepackage{graphicx} \usepackage{colortbl} \usepackage{color} \usepackage{caption} \usepackage{pgfplots, pgfplotstable} \usetikzlibrary{arrows} \usepackage{amsmath} \usepackage{multirow} \usepackage{booktabs}  \usepackage{filecontents} \definecolor{OgAns}{rgb}{0, 0.8, 0.4}  \begin{filecontents}{testdata.dat} 1   30 2   44 4   26 3   39 \end{filecontents}  \begin{document} \begin{figure} \begin{tikzpicture}         \begin{axis}[                ybar stacked,             ymin=0,             ymax=100,             bar width=5pt,             legend style={at={(0.35, -0.4)},anchor=south west},             legend columns=-1                       ]           \addplot[ybar,fill=OgAns]  file {testdata.dat};          \end{axis}     \end{tikzpicture} \end{figure}   \end{document} Finding an uncountable chain of subsets the integers How to find an uncountable subset of $P(\mathbb{N})$ such that every two elements of it can be compared. In fact, give an uncountable subset of $P(\mathbb{N})$ such that has totality property. We mean by $P(\mathbb{N})$, the powerset of natural numbers set $\mathbb{N}$. Give a combinatorial proof to show the following for all integers $n \geq 2$. $$2^{n-2} n (n -1) = \sum\limits_{k=2}^n k (k - 1) \binom{n}{k}.$$  I'm completely stumped. I just have no idea how to do this. What I've tried so far has been simplifying the right hand side slightly to $\sum\limits_{k=2}^n \binom{n}{k - 2}$, and then proving that this somehow is equal to some manipulation of the left hand side. I can't seem to find any breakthroughs that way though.  If anyone could help out or point me in the right direction that would be great.  EDIT: I've actually just realized my simplification of the right hand side is wrong. Now I'm even more stuck. What Is the Real Name of the #? I used to say "sharp sign" to refer to the # sign.   Today a friend told me that the correct term is number sign or hash sign or even just hash.  What is the difference between these options and what's the correct usage of the names for this sign? "Unable to locate package" while trying to install packages with APT When I try to install any package through the command line, I get an error.   $ sudo apt-get install &lt;package&gt; Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package &lt;package&gt;   Can anyone help me on this? The graph of the function $f (x)$ is given.  How many different real roots does the $f (4-3x^2)=0$ equation have?  Here is possible solution:  $$\Bigg [{4-3x^2=-2 \\ 4-3x^2=4} \Longrightarrow x=\left\{0,\sqrt 2,- \sqrt 2\right\} $$  Then, here is different solution:  $$f(x)=x^2-2x-8$$ $$f(4-3x^2)=0\Longrightarrow (4-3x^2)^2-2(4-3x^2)-8=0 \Longrightarrow 9x^4-18x^2=0 \Longrightarrow x=\left\{0,\sqrt 2,- \sqrt 2\right\} $$   Problematic point. Here, I assumed the function is quadratic. But, obviously, this function may not be quadratic.  My questions:  Question $-1:$ Is the first solution completely correct?  Question $-2:$ Can we say that, the second solution is completely and definitely wrong? If so, is it possible to add something to this method and turn it into the right solution?