I working on macOS Mojave 10.14.5  I am new to macOS and I don't know much about installing different versions. I can't dare to uninstall the current as I am afraid to lose my file and installed packages.   how can I safely downgrade to 10.11 or 10.10?  Updates: info about my MacBook:   MacBook Pro (Retina, 13-inch, Late 2013)  The reason why I want this is that I want to install wifi USB adapter but it seems that it's only compatible with os 10.11 or below that. Having this wireless adapter working is so much important to me though.   Adapter details:  EDUP 802.11n USB Wireless  Model : EP-N8553
Sometimes it's hard to search for older versions of macOS &amp; OS X  on the App Store.  This is an attempt to provide the canonical QA for this issue, as per the Meta QA -  I expect it to be modified over time to hopefully become a complete information resource.  How can I get any older version of a Mac OS to be able to run as a VM, or to reinstall on my Mac?
What are the Alternatives For RemasterSys? Unicode filenames on Windows with Python & subprocess.Popen() can you help me to do a difference of CDF? I have 2 CDF's with equal number of points that I want to compare. These are from:   Temperature of 1 month from 2012 Mean temperature across months   What can I do to obtain this difference, this is from the formula of Finkelstein-Schafer Calculate the components of a unit vector that lies in the xy-plane and makes equal angles with the positive directions of the x- and y-axes It's just a doubt.  $\vec { A } = A \hat{ x }  + A\hat { y} $  $ A\hat { y} =A\hat{ x} $  $\vec { A } = A \hat { x }  + A\hat { x} $  Now finding the magnitud of the vector,  $A=\frac { 1 }{ \sqrt { 2 }  } $  So the components of the unit vector are:  $\vec { A } = \frac { 1 }{ \sqrt { 2 }  } \hat { x } +\frac { 1 }{ \sqrt { 2 } } \hat { y} $  Is my answer right? I applied for a 90-day visa and got a long-term visit, single-entry tourist visa. The date given is 09-March-2015, and it's valid until 07-May-2015.  My agent says the 7th is the latest date I can travel to Dubai; once I enter I need to count 90 days. I entered on the 10th of March.    Is it true, or where can I get it checked?    Can I stay for another month, or do I need to leave before the 7th of May? What DC motor specs do I need to lift a weight with certain gear configuration How can I give a user one password for normal usage when logging in, and another password for system administration and sudo access? I want one user to have two passwords. Command-line to switch between profiles in gnome-terminal I created a new profile for gnome-terminal and I can switch between &quot;Implicit&quot; profile and the new created profile as you can see in the below image:  Now I wonder how can I switch between profiles using a command-line/script or maybe using a shortcut for this.  Note: Solutions like: gnome-terminal --tab-with-profile=Implicit &amp;&amp; exit   are excluded because I prefer not to close and open another terminal or get another terminal window in this process of changing the profile. How do I remove a property from a JavaScript object? Say I create an object as follows: let myObject = {   &quot;ircEvent&quot;: &quot;PRIVMSG&quot;,   &quot;method&quot;: &quot;newURI&quot;,   &quot;regex&quot;: &quot;^http://.*&quot; };  How should I remove the property regex to end up with new myObject as follows? let myObject = {   &quot;ircEvent&quot;: &quot;PRIVMSG&quot;,   &quot;method&quot;: &quot;newURI&quot; }; How many solutions for an equation with simple restrictions I'm working on an assignment in which I have to count the number of solutions for this particular equation: $$x_1+x_2+x_3+x_4=20$$for non negative integers with $x_1&lt;8 $ and $x_2&lt;6$   I'm aware that this kind of a task isn't that complicated, but I don't get combinatorics in general that well.  So I've tried two following approaches to get this done.  Firstly I tried to substitute the variable x:  $x_1+x_2+x_3+x_4=20 \Leftrightarrow y_1+y_2+y_3+y_4=34$  in which $y_1=x_1+8$ and $y_2=x_2+6$ (casue $x_1=y_1-8$ and $x_2=y_1-6$) Following this approach the total number of possible solutions would be  $${34+3 \choose 3} $$  But I'm not sure if its the right solution.  The second approach is to sum all of the possible values that $x_1$ and $x_2$ could possibly take, also $x_1=0,1,2,3,4,5,6,7$ and $x_2=0,1,2,3,4,5,6$ And then  count all the possibilities for each of the variables $${20 -x_1-x_2+1\choose 1}$$ and sum them together like this: $${21\choose 1}+{20\choose 1}+{19\choose 1}+{18\choose 1}+... $$ and so on...  I'm sure I'll get the correct number with this one, but I'm not feeling like summing all of this possibilities. There's got to be a better, more elegant way to deal with this.  My professor gave me a hint that I should do it using the complement. Change pivot or local origin of an object How can I change the local origin of an object, without changing the object location in the world space.  This is the object located at position (0,0,0) in the world space    This is the same object located at position (0,1,0) in the world space, but with its local origin offset so that the object is in the same place    Is there a way to do this in a single step? I see this often in the build scripts of projects that use autotools (autoconf, automake).  When somebody wants to check the value of a shell variable, they frequently use this idiom:  if test "x$SHELL_VAR" = "xyes"; then ...   What is the advantage to this over simply checking the value like this:  if test $SHELL_VAR = "yes"; then ...   I figure there must be some reason that I see this so often, but I can't figure out what it is. Every proper ideal is contained in a maximal ideal, in a commutative ring with identity. The statement is:     In a commutative ring with 1, every proper ideal is contained in a maximal ideal.   and we prove it using Zorn's lemma, that is, $I$ is an ideal, $P=\{I\subset  A\mid A\text{ is an ideal}\} $, then by set inclusion, every totally ordered subset has a bound, then $P$ has a maximal element $M$.  My question is why $M$ must contain $I$? Definitions and usage of Covariant, Form-invariant & Invariant? Just wondering about the definitions and usage of these three terms.  To my understanding so far, "covariant" and "form-invariant" are used when referring to physical laws, and these words are synonyms?  "Invariant" on the other hand refers to physical quantities?  Would you ever use "invariant" when talking about a law? I ask as I'm slightly confused over a sentence in my undergrad modern physics textbook:     "In general, Newton's laws must be replaced by Einstein's relativistic laws...which hold for all speeds and are invariant, as are all physical laws, under the Lorentz transformations." [emphasis added]      ~ Serway, Moses &amp; Moyer. Modern Physics, 3rd ed.   Did they just use the wrong word? One of the products being shown a CES is a  intended to let you charge a tablet from a laptop USB port that normally wouldn't work because it didn't provide enough power.  The CNET writeup implies that it's actually boosting the power output from the port beyond the normally available amount.  This seems improbable to me because the ports should have current protection to protect themselves from shorts.  Also, if it was possible to bypass the current limit externally, I'd've expected at least some tablet vendors to have included the ability to do so directly in their cables.  One possibility that occurs to me is that the dongle is just spoofing responses to the tablet when it queries the laptop about the maximum power it can deliver while only providing a trickle charge that the tablet would otherwise reject as too slow to bother with. Cancelling upvote on comment? As mentioned on :     For something that can be done so   easily by accident, there should be   the ability to undo mistakes.   I know that I have clicked several times on a comment up-vote without actually wanting to.  I would suggest being able to cancel the up-vote (maybe only for a couple of minutes or even less than a minute, no problem, as long as I can undo a miss-click). What is an intuitive explanation of the Expectation Maximization technique? Is it possible to make my laptop's screen act as a second monitor for my desktop computer? "define:" oneboxing selects completely bogus data I found this weird word, "burke", and decided to check it out. It turned out it was an alternative spelling of "berk". This is what define: berk in chat expanded to:    So, according to that, "berk" as a noun can mean "a fool, prat, twit", or "berk", or "berk", or "berk". Wow, who would have thought "berk" might mean berk. Three times, just to be sure.  That got me really curious so I checked the wiktionary page directly. It shows three meanings for "berk": the same as meaning #1 that was oneboxed, plus two others that are not at all simply stated as "berk".  Further down from there we can find the other three "berks". Number three, for instance, is easy to trace since "indefinite plural berkë" seems quite greppable. And it turns out that it's Albanian. ASP.NET Web Site or ASP.NET Web Application? When I start a new ASP.NET project in Visual Studio, I can create an ASP.NET Web Application or I can create an ASP.NET Web Site.  What is the difference between ASP.NET Web Application and ASP.NET Web Site? Why would I choose one over other?  Is the answer different based on which version of Visual Studio I am using?