Handoff renders two-factor authencation worthless? I noticed that when I enabled two-factor authentication for my Apple ID and have handoff turned on, the code pops up on the mac where I'm seeking the two factor. Seems like it renders the two-factor worthless. Isn't the point it have it go to another device, separate from the login device?  I guess the obvious solution is to not have handoff on the mac?
Does iCloud Two-factor authentication send a code to the same device as a log in request? My Apple-ID (e.g., on  ) is set up to require entry of a 6-digit code sent to my registered Apple products.  This code is being sent to the same device I'm currently requesting to log in. I feel this absolutely defeats the purpose of this 2-Factor Authentication: If a person knows my password, this person can receive the code on that device, and access my apple account without any problems.  Is this a bug or can I set up / change how this security step works?
Why $∀x(P(x)→Q)$ is equivalent to $∃xP(x)→Q$ Given $x$ occurs free in $P$. If $x$ does not occur free in $Q$, then $∀x(P(x)→Q)$ is semantically equivalent with $∃xP(x)→Q$. How to understand this statement. And also, need an example to show that the formula will not necessarily be equivalent if $x$ does occur free in $Q$.  I guess what struggles me is I'm not quite understand what does "free" mean in this case. But it would be better to have answer for the above question. I caught an Eevee, which of its evolutions will it evolve into? So I just caught an Eevee. Now, I need 25 candies to evolve it. The fact is that in the GameBoy color versions, that Pokémon needed a stone to evolve instead of experience. Depending of the stone he was fed with (thunder, water or fire), he was evolving in a different Pokémon.   Is the stone feature also in Pokémon Go? If not, what decide the evolution of this Pokémon?   Bonus point : If it's possible, how can I get a stone? Removing overlapping/duplicate polygons in same layer using QGIS? Where can I find out about Stack Overflow history? I'd like to know how Stack Overflow and other sites started - which was first, who initiated it (OK, that's on the link below) and why, how the different sites evolved, how the rules evolved, etc.  Where can I find such information?  Of course, I know I can look at  for a brief overview but I'm wondering if there is info on this site, particularly more detailed.. Let $G$ be a finite group of order $n\ge2$. Which of the following statements are true? a. There always exists an injective homomorphism from $G$ into $S_n$. b. There always exists an injective homomorphism from $G$ into $S_m$ for some $m\lt n$. c. There always exists an injective homomorphism from $G$ into $GL_n(R)$.  I think b. is right (don't know how to prove though). I also think that c. is false. But not sure. How to revert an update? The latest xorg update was a big regression for me on a dual display setup. Is there a simple way to revert to the previous version?  I'm on Lucid Lynx. Suppose John has 5 sweets. Is there any difference between the following two sentences?     Jack has 3 times as many sweets as John.      Jack has 3 times more sweets than John.   I prefer the first construction and would know unambiguously that Jack has 15 sweets in this case. However in the second construction I would be inclined to think that Jack has 20 sweets, since it seems to suggest 15 sweets in addition to the original 5. Is $f(x,y)=(xy)^{2/3}$ differentiable at $(0,0)$? I looked at the graph of $f(x,y)=(xy)^{2/3}$ at the origin, and no matter how far I zoom in it has four corners along $x=\pm y$, so it doesn't look like it is differentiable as $z=0$ doesn't look like a tangent plane.  I also found that its partial derivatives are not continuous at $(0,0)$, e.g.  $$ \lim_{(ky^2,y) \to (0,0)} \frac{\partial f}{\partial x} = \lim_{(ky^2,y) \to (0,0)} \frac{2}{3}x^{-\frac{1}{3}}y^{\frac{2}{3}} = \frac{2}{3}k^{-\frac{1}{3}} $$ (although $\frac{\partial f}{\partial x}(0,0) = \frac{\partial f}{\partial y}(0,0) = 0$)  I also tried to prove/disprove its differentiability by definition, and for it to be differentiable I need $$ \lim_{(x,y) \to (0,0)} \frac{f(x,y)-0}{\sqrt{x^2+y^2}} =0 $$ but then I got stuck. Am I even on the right track?  [UPDATE] I need to do the same thing for $f(x,y)=(xy)^{\frac{1}{3}}$... I think the answer is that $(xy)^{2/3}$ is differentiable but $(xy)^{1/3}$ is not, according to my professor but I'm not sure I am using Ubuntu 16.04 LTS . I have python3 installed. There are  two versions installed, python 3.4.3 and python 3.6 . Whenever I use python3 command, it takes python 3.4.3 by default. I want to use python 3.6 with python3. python3 --version shows version 3.4.3 I am installing ansible which supports version &gt; 3.5 . So, whenever, I type ansible in the terminal, it throws error because of python 3.4 sudo update-alternatives --config python3 update-alternatives: error: no alternatives for python3 What is the proof that given a set of $n$ elements there are $2^n$ possible subsets (including the empty-set and the original set). INC instruction vs ADD 1: Does it matter? What is the difference between [@] and [*] when referencing bash array values? says:  If the index number is @ or *, all members of an array are referenced.  When I do this: LIST=(1 2 3) for i in &quot;${LIST[@]}&quot;; do   echo &quot;example.$i&quot; done  it gives the desired result: example.1 example.2 example.3  But when I use ${LIST[*]}, I get example.1 2 3  instead. Why? Edit: when using printf, @ and * actually do give the same results. How can I output a list of all installed packages with installation date and additional information? $x^p-c$ has no root in a field $F$ if and only if $x^p-c$ is irreducible? Hungerford's book of algebra has exercise $6$ chapter $3$ section $6$ [Probably impossible with the tools at hand.]:     Let $p \in \mathbb{Z}$ be a prime; let $F$ be a field  and let $c \in  F$. Then $x^p - c$ is irreducible in $F[x]$ if and only if $x^p - c$   has no root  in $F$. [Hint: consider two cases: char$(F) = p$ and   char$(F)$ different of $p$.]   I have attempted this a lot. Anyone has an answer? How does Earth's interior dynamo work? I'm interested in getting a basic physical understanding of how Earth's magnetic field is generated. I understand that it's a "dynamo" type of effect, driven by convection currents in the molten outer core. These currents cause charges to move, and this generates the field.  However, what I can't find a good explanation of is why there is a separation of charges in the first place. Presumably, moving neutrally charged molten iron would have the same effect as moving any other neutrally charged thing, i.e. it wouldn't create a field.  And presumably, if the fluid wasn't moving then it would become neutral pretty quickly, since molten iron is a good electrical conductor.  So am I right in thinking that the charge separation is the result of positive feedback, in that an intial deviation from neutrality would generate a field, and this would (somehow) cause a greater separation of charges, resulting in a kind of self-maintaining charge separation?  Or is there another explanation?  In either case, does anyone know of a good resource that explains the basic principles in physical terms?  I know that the interior dynamo is a very complex phenomenon, but I'd like something that gives a good physical picture of how the electromagnetic and fluid dynamical phenomena interact, rather than diving straight into partial differential equations. is piped ls the same as ls -1? ls returns output in several columns, whereas ls|cat returns byte-identical output with ls -1 for directories I've tried. Still I see ls -1 piped in answers, like ls -1|wc -l. Is there ever a reason to prefer ls -1? Why does ...|cat change the output of ls? How can I include a YAML file inside another? So I have two YAML files, "A" and "B" and I want the contents of A to be inserted inside B, either spliced into the existing data structure, like an array, or as a child of an element, like the value for a certain hash key.  Is this possible at all? How? If not, any pointers to a normative reference? Fast way to copy a large file on a LAN I am having some trouble with NFS, and I'd like to try using just plain old TCP.  I have no idea where to begin, though.  Hardware-wise, I am using an ethernet crossover cable to network two netbooks.  To network them, I type  $ sudo ifconfig eth0 192.168.1.1 up &amp;&amp; ping -c 10 -s 10 192.168.1.2 &amp;&amp; sudo /etc/init.d/nfs-kernel-server start   on the first netbook and  $ sudo ifconfig eth0 192.168.1.2 up $ ping -c 10 -s 10 192.168.1.1 $ mount /mnt/network1   on the second  where /mnt/network1 is specified in /etc/fstab as  192.168.1.1:/home /mnt/network1 nfs noauto,user,exec,soft,nfsvers=2 0 0  as well as in /etc/exports (using the syntax of that file), on the first netbook.  The above works fine, but the files and directories are huge. The files average about half a gigabyte a piece, and the directories are all between 15 and 50 gigabytes.   I'm using rsync to transfer them, and the command (on 192.168.1.2) is  $ rsync -avxS /mnt/network1 ~/somedir   I'm not sure if there's a way to tweak my NFS settings to handle huge files better, but I'd like to see if running an rsync daemon over plain old TCP works better than rsync over NFS.  So, to reiterate, how do I set up a similar network with TCP?  UPDATE:  So, after a good at few hours of attempting to pull myself out of the morass of my own ignorance (or, as I like to think of it, to pull myself up by my own bootstraps) I came up with some useful facts.  But first of all, what led me on this rabbit trail instead of simply accepting the current best answer was this: nc is an unbelievably cool program that resolutely fails to work for me. I've tried the netcat-openbsd and netcat-traditional packages with no luck whatsoever.  The error I get on the receiving machine (192.168.1.2) is:  me@netbook:~$ nc -q 1 -l -p 32934 | tar xv Can't grab 0.0.0.0:32934 with bind tar: This does not look like a tar archive tar: Exiting with failure status due to previous errors   route gives:  me@netbook:~$ route Kernel IP routing table Destination     Gateway         Genmask         Flags Metric Ref    Use Iface default         dir-615         0.0.0.0         UG    0      0        0 wlan0 link-local      *               255.255.0.0     U     1000   0        0 eth0 192.168.0.0     *               255.255.255.0   U     2      0        0 wlan0 192.168.1.0     *               255.255.255.0   U     0      0        0 eth0   But, here's the good news: having the static IP addresses set in /etc/network/interfaces, which I started doing while trying to get nc working, fixed all my NFS problems and rekindled my love for NFS.  The exact configuration I used (with 192.168.1.1 for the first netbook, of course) was:  auto eth0 iface eth0 inet static address 192.168.1.2 netmask 255.255.255.0   With those settings, the two netbooks will be able to ping each other directly after being booted up, without even an ifup.  Anyway, I'd still really like to see nc in action, so I'm hoping someone help me debug this process. Where can I find the restrictions and easements that apply to a given UK Rail Ticket? UK rail ticketing isn't always the simplest thing in the world, but the basics aren't too hard to learn. There are  tickets valid at any time of the day, those available only outside of peak hours (typically after 9 and perhaps not in the evening rush hour), tickets only available at quiet times, tickets valid only on one train. These are mostly, but not always, valid in flavours of single (one way), day return (out and back the same day-ish), and (period) return (out on a given day, back within a month). That's it broadly, but you'll notice there's a bit of variation in even just those...  Next up, there are rules on what sort of route you can take. These largely revolve around , not doubling back, direct trains normally being fine, and not taking too long a route if there's a choice. (There's a whole art to making the most of that though, but this isn't the question for that!)  On top of all that, certain routes and/or stations will have additional restrictions, or easements where default restrictions are lifted. For example, one station might be in an area where the default rule is "off peak tickets valid after 9am", then has an additional restriction "off peak tickets to London only valid on trains arriving after 10am", and an easement "off peak tickets to stations along the insert line name here valid after 08:45".  By looking up these restrictions and easements, it's sometimes possible to save money on your journey. In the example above, you might assume you'd need a peak time ticket to travel on the 08:54 to a station along the local branch line, but the easement actually allows you to travel on a cheaper off-peak ticket instead.  How do you go about looking up what easements apply to a given ticket for a journey, and equally what extra restrictions (eg evening peak times or not-valid-via) apply? The Problem  Currently if I flag a post, I cannot check the status of the flag unless I have prior helpful flags. This means, for example, that a new user who wants to check the status of his first flag cannot do so while it is pending (active).  This feature request is based on my experience on MSO, where I wanted to check the status of my flag but could not get to the summary page without cheating (tweaking my SO link to work with MSO). It also stems from this question, where the OP indicates he had the same issue:   My Proposal  If I have flagged any post, then show me a "flags" link (red arrow in image below). If I have any helpful flags, then the number of helpful flags should be displayed (blue arrow). If I have not flagged anything, then neither should be displayed (as with current site functionality).