What is the difference between "I did play " and "I played" according to the British English?
The two sentences here both indicate that, at some point in the past, I performed some work:   I did work I worked   What is the difference between these two sentences? Does constructing one with did and the other with a simple past change the meaning?
Why is the sky never green? It can be blue or orange, and green is in between! I, like everybody I suppose, have read the  why the colour of the sky is blue:     ... the two most common types of matter present in the atmosphere are   gaseous nitrogen and oxygen. These particles are most effective in   scattering the higher frequency and shorter wavelength portions of the   visible light spectrum. This scattering process involves the   absorption of a light wave by an atom followed by reemission of a   light wave in a variety of directions. The amount of multidirectional   scattering that occurs is dependent upon the frequency of the light.   ... So as white light.. from the sun passes through our atmosphere,   the high frequencies become scattered by atmospheric particles while   the lower frequencies are most likely to pass through the atmosphere   without a significant alteration in their direction. This scattering   of the higher frequencies of light illuminates the skies with light on   the BIV end of the visible spectrum. Compared to blue light, violet   light is most easily scattered by atmospheric particles. However, our   eyes are more sensitive to light with blue frequencies. Thus, we view   the skies as being blue in color.   and why sunsets are red:     ... the light that is not scattered is able to pass through our   atmosphere and reach our eyes in a rather non-interrupted path. The   lower frequencies of sunlight (ROY) tend to reach our eyes as we sight   directly at the sun during midday. While sunlight consists of the   entire range of frequencies of visible light, not all frequencies are   equally intense. In fact, sunlight tends to be most rich with yellow   light frequencies. For these reasons, the sun appears yellow during   midday due to the direct passage of dominant amounts of yellow   frequencies through our atmosphere and to our eyes.      The appearance of the sun changes with the time of day. While it may   be yellow during midday, it is often found to gradually turn color as   it approaches sunset. This can be explained by light scattering. As   the sun approaches the horizon line, sunlight must traverse a greater   distance through our atmosphere; this is demonstrated in the diagram   below. As the path that sunlight takes through our atmosphere   increases in length, ROYGBIV encounters more and more atmospheric   particles. This results in the scattering of greater and greater   amounts of yellow light. During sunset hours, the light passing   through our atmosphere to our eyes tends to be most concentrated with   red and orange frequencies of light. For this reason, the sunsets have   a reddish-orange hue. The effect of a red sunset becomes more   pronounced if the atmosphere contains more and more particles.   Can you explain why the colour of the sky passes from blue to orange/red skipping altogether the whole range of green frequencies?  I have only heard of the legendary 'green, emerald line/ flash'     that appears in particular circumstances     Green flashes are enhanced by mirage, which increase refraction... is more likely to be seen in stable, clear air,... One might expect to see a blue flash, since blue light is   refracted most of all, and ... is   therefore the very last to disappear below the horizon, but the blue   is preferentially scattered out of the line of sight, and the   remaining light ends up appearing green   but I have never seen it, nor do I know anybody who ever did. I am trying to do a new environment or command (i tried both) where i can put in the name, description and code of a Method in c++ and it gives me a new section with the MethodName, the code listed and the description below. But i am not able to use the listings environment in a new command or new environment.. Consider my MWE   \documentclass[a4paper,11pt]{article} \usepackage{listings}  \newcommand{\method}[3] { \section{#1}\label{#1} \begin{lstlisting} #2 \end{lstlisting} #3 }   \begin{document}  \method{MethodName}{Method Void MethodName()}{Description of the Method blablabla}  \end{document}   How can I fix this?   I would prefer to do it using a macro since I don't need an ending. I'm using 17.04 ( Clean Install ), and as far as I remember, every try to install any sofware- it fails with that error code.  I tried sudo apt-get update &amp;&amp; apt-get upgrade and problem persists.  any idea why?   edit: Using software Updater gave this result :   edit : output of update  guy@LG-LAPTOP:~$ sudo apt-get update &amp;&amp; apt-get upgrade [sudo] password for guy:  Ign:1 http://il.archive.ubuntu.com/ubuntu zesty InRelease Ign:2 http://il.archive.ubuntu.com/ubuntu zesty-updates InRelease               Ign:3 http://il.archive.ubuntu.com/ubuntu zesty-backports InRelease             Err:4 http://il.archive.ubuntu.com/ubuntu zesty Release                           503  Service Unavailable Get:5 http://security.ubuntu.com/ubuntu zesty-security InRelease [89.2 kB]      Err:6 http://il.archive.ubuntu.com/ubuntu zesty-updates Release                   503  Service Unavailable Get:7 http://archive.canonical.com/ubuntu zesty InRelease [10.2 kB]             Err:8 http://il.archive.ubuntu.com/ubuntu zesty-backports Release                 503  Service Unavailable Get:9 http://archive.canonical.com/ubuntu zesty/partner Sources [1,416 B]       Get:10 http://archive.canonical.com/ubuntu zesty/partner amd64 Packages [1,616 B] Get:11 http://archive.canonical.com/ubuntu zesty/partner i386 Packages [1,612 B] Get:12 http://archive.canonical.com/ubuntu zesty/partner Translation-en [708 B] Get:13 http://security.ubuntu.com/ubuntu zesty-security/main amd64 DEP-11 Metadata [11.7 kB] Get:14 http://security.ubuntu.com/ubuntu zesty-security/main DEP-11 64x64 Icons [9,219 B] Get:15 http://security.ubuntu.com/ubuntu zesty-security/universe amd64 DEP-11 Metadata [14.4 kB] Get:16 http://security.ubuntu.com/ubuntu zesty-security/universe DEP-11 64x64 Icons [31.0 kB] Reading package lists... Done                                          E: The repository 'http://il.archive.ubuntu.com/ubuntu zesty Release' does no longer have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. E: The repository 'http://il.archive.ubuntu.com/ubuntu zesty-updates Release' does no longer have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. E: The repository 'http://il.archive.ubuntu.com/ubuntu zesty-backports Release' does no longer have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. guy@LG-LAPTOP:~$    output of apt get  guy@LG-LAPTOP:~$ sudo apt-get install putty Reading package lists... Done Building dependency tree        Reading state information... Done The following additional packages will be installed:   putty-tools Suggested packages:   putty-doc The following NEW packages will be installed:   putty putty-tools 0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded. Need to get 661 kB of archives. After this operation, 2,713 kB of additional disk space will be used. Do you want to continue? [Y/n]  Err:1 http://il.archive.ubuntu.com/ubuntu zesty/universe amd64 putty-tools amd64 0.67-3   503  Service Unavailable Err:2 http://il.archive.ubuntu.com/ubuntu zesty/universe amd64 putty amd64 0.67-3   503  Service Unavailable E: Failed to fetch http://il.archive.ubuntu.com/ubuntu/pool/universe/p/putty/putty-tools_0.67-3_amd64.deb  503  Service Unavailable E: Failed to fetch http://il.archive.ubuntu.com/ubuntu/pool/universe/p/putty/putty_0.67-3_amd64.deb  503  Service Unavailable E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing? guy@LG-LAPTOP:~$ So basically this proof centers around proving that (S,*) is a group, as it's quite easy to see that it's abelian as both addition and multiplication are commutative. My issue is finding an identity element, other than 0. Because if 0 is the identity element, then this group won't have inverses.  The set explicitly excludes -1, which I found to be its identity element, which makes going about proving that this is a group mighty difficult. I noticed in this thread the OP successfully managed to connect a 30" cinema display to the new Macbook Pro USB-C, with full resolution:    I have the official Apple dual DVI adapter, going to a displayport > USB-C adapter like yours, however the screen does not fire up.  I then tried a multi adapter instead of the single displayport > USB-C, which worked but only at 1280 resolution:    Would the official Apple Dual DVI adapter not work? Which singular names ending in “s” form possessives with only a bare apostrophe? How to count the number of occurrences of each item in an array? Fourier series of Log sine and Log cos How can I use $variable in a shell brace expansion of a sequence? I want to use $var in a shell brace expansion with a range, in bash. Simply putting {$var1..$var2} doesn't work, so I went "lateral"...   The following works, but it's a bit kludgey.    # remove the split files echo rm foo.{$ext0..$extN} rm-segments &gt; rm-segments source rm-segments   Is there a more "normal" way? Was Stack Exchange named after Experts Exchange? Was Stack Exchange named after Experts Exchange, or is the former using the word "Exchange" a coincidence? Do Stack Overflow and other Stack Exchange sites have an app I can use? I like using Stack Overflow (or any other Stack Exchange sites) and was wondering if there was an app I could install on my phone or other device that would allow me to use the site on-the-go or straight from my desktop.  Some systems to consider:   Windows 8 Android iPhone/iOS   What are some apps that I could install to my computer or phone to enhance my Stack Exchange experience? Need help with a work around I need to take the 'Office' display of the 'Created By' column and display the first 5 digits of it so that my flows can run a conditional check on it. The reason is that Microsoft flows has all the 'Created By' dynamic contents besides 'Office'.  I figured simple enough I'll just do a calculated column on the SharePoint list. Then I find out that 'Created By' cannot be used in calculated columns.   So I figured I'll have my PowerApp write the Users 'Office' as a default to a field when submitting a form and calculate it off that column. Unfortunately PowerApps only has User().FullName, Email, and Image.   I have pretty much exhausted the options for a workaround that my knowledge will allow. Hopefully someone might have some ideas. Prove $f(S \cup T) = f(S) \cup f(T)$ Make cd automatically ls I find that I often do the following:  %&gt; cd bla/bla %&gt; ls   I would like it that whenever I cd into a directory it automatically does an ls.  I fiddled with my .bashrc for a while, but couldn't figure out how to make it happen. I recall a short lived TV show that I think was broadcast on the British TV channel ITV in the late 90s or early 2000s and it was about time travel. It was set in Britain in relatively modern times. The scene that really sticks in my head is when the protagonist goes to use their time travelling machine they go in to a room where the machine is and they close all the windows. The windows have latches on them and by closing the window it creates a circuit. By closing all the latches the circuit is complete and the machine is able to be activated. I don't know if it's much to go on, but it's been really bugging me for ages. Why can charges outside be ignored in Gauss's Law? In MIT's 8.02 course, it is shown in lecture 3 that we can derive Gauss's Law from Coulomb's to get  $ \phi = \oint \vec{E} \cdot \vec{dA} = \frac{Q_{enc}}{\epsilon_{0}} $  However, in the lecture, it was assumed that there were no charges outside the surface. Later, Gauss's Law was used and the charges outside the sphere were ignored.  I've been thinking about it and came across .  The first answer by user levitopher helped a bit. I think that the lecture's argument still holds when there are charges outside because $ \vec{E} $ is added vectorially.  Suppose we have $ Q_{enc} $ in a sphere and $ Q_{out} $ outside the sphere. Then,  By definition, $ \phi = \oint (\vec{E_{Q_{enc}}} + \vec{E_{Q_{out}}}) \cdot \vec{dA} $ $ = \oint \vec{E_{Q_{enc}}} \cdot \vec{dA} + \oint \vec{E_{Q_{out}}} \cdot \vec{dA}$ $ = \oint \vec{E_{Q_{enc}}} \cdot \vec{dA} + 0 $ $ = \frac{Q_{enc}}{\epsilon_{0}} $  This assumes that $ \oint \vec{E_{Q_{out}}} \cdot \vec{dA} = 0 $ because any field lines that go in must come out (hand wavy but I'm just going to accept it for now).  I'd just like to know if this argument is sound. $a,b,m,n$ be positive integers such that g.c.d.$(a,b)=1$ and $a^m+b^m|a^n+b^n$ , then $m|n$? Let $a,b,m,n$ be positive integers such that g.c.d.$(a,b)=1$ and $a^m+b^m|a^n+b^n$ , then is it true that $m$ divides $n$ ? Odd behavor with POSIXct/POSIXlt and subsecond accuracy Is "has or will read" grammatical? (used to show two posts from MSE)   (there used to be a list of the accounts)   (it was there) seems to be fixed