what is the differene between "class" and "struct"?
What are the differences between struct and class in C++?
Categorical Quotient and group actions I am trying to practice calculating categorical quotients and I ran into this example. I am unable to get the answer and was wondering if someone can help?  Let $G = Z/3Z =$ $\{1, \omega, \omega^2\}$, where $\omega$ is a cube root of unity. Let $G$ act on $𝔸^{2}$ via $\omega(x, y) = (\omega x, \omega y)$. Find the categorical quotient of $𝔸^{2}$ by G. Construction of uncountably many non-isomorphic linear (total) orderings of natural numbers I would like to find a way to construct uncountably many non-isomorphic linear (total) orderings of natural numbers (as stated in the title).  I've already constructed two non-isomorphic total orderings. They are $$ 1 &lt; 2 &lt; 3 &lt;\ldots\\ 1 &gt; 2 &gt; 3 &gt;\ldots $$ where "$&lt;$" and "$&gt;$" are  strict total ordering relations.  Thanks in advance for your help. Why does Earth behave like Natural Bar Magnet? What is the reason for the Earth to behave like a bar magnet and have poles (North and South poles)? To install the graphics driver I need to exit GUI / Gnome and go to the terminal. How can I do this in Ubuntu 18.04? Ctrl(STRG)+Alt+F1...F7 does not work, neither on the desktop, nor on the login screen... What does the 'cosmological constant' represent? Newtons theory of gravity involves a gravitational constant $G$, however one does not refer to it directly, we speak instead of gravity or the force of gravity.   Now Einsteins introduced a  in his equation for GR, and ever since it's been referred to as such; however, this usage seems strange to me, given the above parallel; it seems to me we ought to be referring to something physical, which can then be quantified and whose quantification involves the cosmological constant.   Does the cosmological constant then refer to a cosmological force? A force that is, contra gravity, repulsive? And which is even weaker than gravity, kicking in on the scale of galaxies rather than solar systems? What is the greatest integer that divides $p^4-1$ for every prime number $p$ greater than $5$? What is the greatest integer that divides $p^4-1$ for every prime number $p &gt; 5$?  This was on a practice math GRE so it's probably really easy. Keyboard shortcut to autocomplete the user in comments Is it possible to run Android apps on Ubuntu? And I don't mean inside an emulator, but natively, as you would with any other application installed using the Ubuntu Software Center. If a tag wiki becomes inaccessible due to a tag being eliminated, is the data destroyed? Or would it be able to be recovered by just recreating the tag?  On Gaming we had one tag for a particularly difficult case that a wiki entry was written for. There has been some debate as to what we should keep the tag as, which has led to the only instance of the tag being renamed a few times and eventually left on a new tag. The nightly script eventually cleaned out the original tag, and the wiki is inaccessible. So would I be able to retrieve this by reverting to the original tag, or is a rewrite of the wiki necessary? While watching  play for the gold medal in London 2012, I noticed Williams was going about her business while Sharapova was grunting each time she hit the ball.  After doing some , grunting in tennis dates back to 1962. Although men grunt, women draw more attention due to their high-pitched grunts. In addition, there is an initiative to eliminate excess grunts in the next generation of tennis players.  Another quote from said research says:     "I have not found in my 32 years anybody who says grunting or not   grunting has an empirically positive or negative effect on performance   -- it's all about belief system."   What is this "belief system?"  If grunting is not related to performance, why do tennis players do it excessively? Prove $\sqrt{2}$ is between $\dfrac{a}{b}$ and $\dfrac{a+2b}{a+b}$ Let $a$ and $b$ be positive integers. Show that $\sqrt{2}$ always lies between $\dfrac{a}{b}$ and $\dfrac{a+2b}{a+b}$.  Please give the easy solution as possible. If no spell can reawaken the dead, how did the resurrection stone work? Dumbledore himself said that no spell can reawaken the dead. Isn't that the main objective of the resurrection stone? If one can't reawaken the dead then what is the use of the stone? Surely then one of the Hallows is flawed? Flag counter is missing sporadically I noticed that on both sites where I am a moderator the flag counter is occasionally not showing any flags even when there are flags in the queue. A refresh of the page leads to the correct flag count to be displayed. I noticed this happening when I visited the site for the first time in a few hours, when I was recently active on the site the counter seems to stay accurate. How to make a standalone document with one equation? Get variable from PHP to JavaScript Good textbooks on homological algebra Punctuation of a Direct Quote Is any particular punctuation necessary when a quotation is the subject of a sentence? For example, in the sentence below, should there be a comma after export? Or anything else?     "Laughter is America's most important export" is a well-known quote of Walt Disney's. How can I extract the points from a ListSurfacePlot3D? Exercise $1.8$ of chapter one in Hartshorne. Simplify $\sum (x_i- \mu)^2$ How can I simplify this relation? $$\sum_{i = 1}^m(X_i-\mu)^2=\sum_{i = 1}^m(X_i-\bar{X}_m)^2+m(\bar{X}_m-\mu)^2$$ I know how to set up: $$\sum_{i = 1}^m(X_i-\mu)^2=\sum_{i = 1}^m[(X_i-\bar{X}_m)+(\bar{X}_m-\mu)]^2$$ but when I open the bracket, how do I handle the mixed term? $$2\sum_{i = 1}^m(X_i-\bar{X}_m)(\bar{X}_m-\mu)$$  Thank you!