The difference between $F(a)$ and $F[a]$ when considering fields
$F(x)$ versus $F[x]$ where $F$ is a field
Booking a flight without passport info I have been looking to book a bundle (hotel and flight) with Expedia to Puerto Vallarta MX. When I get to the booking section it does not ask for my passport number. Do they ask for my passport after I book? Or later when the date gets near? My passport is currently being renewed and I want to book my hotel and flight before they sell out but I am afraid it'll ask me for my passport number. Can anyone inform me about this situation? How do I change the computer name? If you have a glass of water, say, three quarters full and you pour it at an angle of say, $45^{\circ}$ with respect to the the table, the water comes out of the glass and goes directly down towards the floor.  However, when the glass is more full, or even three quarters full and the 'angle of pouring' is far less with respect the table, when the water comes out of the glass, rather than going straight down it kind of stays stuck to the glass and travels down the outside of it.  Why does this happen? (I'm sure many of you have observed it yourself by accident and ended up making a mess). For a polynomial $p(z)$, prove there exist $R>0$, such that if $|z|=R$, then $|p(z)|\geq |a_n|R^n/2$ Google chrome is reading characters backwards How to use siunitx with non numerical values? Find the sum of angles without trigonometry? Is it possible to mark the same tag as "Interesting" and "Ignored"? Can you mark the same tag as both interesting and ignored? If you can, what is the resulting appearance of a question with that tag? Proof that $A_n$ the only subgroup of $ S_n$ index $2$. I have what seems to me a very simple proof that $A_{n}$ is the only subgroup of $S_{n}$ of index 2.  Since I've seen other people prove it with what feel like really complicated methods (), I'm wondering if I've overlooked something.  Proof: Let $H$ be any subgroup of index 2 in $S_{n}$.  Then $H\cap A_{n}$ is a normal subgroup of $A_{n}$ and since $A_{n}$ is simple, $H$ is either the trivial or the improper subgroup of $A_{n}$.  If it's the trivial subgroup it doesn't have index 2 in $S_{n}$, and otherwise the theorem is proved. Does the Mordenkainen's Magnificent Mansion spell's mansion exist on a separate plane of existence? In particular: the  spell (PHB, p. 281) states:  [...] The creature can be anywhere on the same plane of existence as you. The spell ends if you or the target are no longer on the same plane. [...]  Can telepathy connect two characters, one inside the extradimensional dwelling created by the  spell and the other in the same plane as the portal to the magnificent mansion? Install on usb external hard drive I am new to ubuntu and i would like some help. I have a laptop with windows 7 installed but i would love to have ubuntu too because it's a great OS. So i would like to install ubuntu on an external usb hard drive (320 - 500 GB) and i have some questions about that :   Do i need a usb external hard drive which will be compatible with ubuntu - linux ? or i can do it with any hard drive  If i make a partition on it for ubuntu staff will i be able to use it and save other staff in the usb hard drive (movies,songs,documents etc) ? If i have ubuntu installed on the usb hard drive will i be able to boot ubuntu from any pc ? Are my changes going to be saved normally or my settings will be lost after shut down ?   Waiting for your answers, if something is not explain well tell me to try explain it better . Thank you! I would like to have an app include a custom font for rendering text, load it, and then use it with standard UIKit elements like UILabel. Is this possible? 9 rows is just way too small by default. Is this a text-editor for ants? Flagging summary improvement: filters Here is my flagging summary on SU:   Your flagging history   32 posts flagged as requiring moderator attention    2 are waiting for review   3 were marked valid   1 were marked invalid   (older flags were not recorded valid/invalid)    2 posts marked as spam    It is too complicated to look for invalid flags. Would it be possible to make filters on the top of the page (like on favorites for example) with:  By date, By type (off-topic, spam, dupes), By status (accepted, pending, rejected)  It would make it easier for reviewers to check their flagging and eventually know what to improve on.  Or is there another easy way to audit this? Geometric meaning of the determinant of a matrix What is the geometric meaning of the determinant of a matrix? I know that "The determinant of a matrix represents the area of ​​a rectangle." Perhaps this phrase is imprecise, but I would like to know something more, please.  Thank you very much. Why is setTimeout(fn, 0) sometimes useful? Logins with only HTTP - are they as insecure as I'm thinking? Recently I was thinking about how websites like gmail and amazon use HTTPS during the login process when accessing your account. This makes sense, obviously, since you're typing in your account username and password and you would want that to be secure. However, on Facebook, among countless other websites, their logins are done with simple HTTP. Doesn't that mean that my login name and password are completely unencrypted? Which, even worse, means that all those people who login to their facebooks (or similar sites) at a wifi hotspot in public are susceptible to anyone getting their credentials using a simple packet sniffer (or something similar)? Is it really that easy? Or am I misunderstanding internet security?  I'm a software engineer working on some web related stuff, and although at the current time I'm not too involved with the security aspect of our software, I knew I should probably know the answer to this question, since it's extremely fundamental to website security.  Thanks! Implement numbering scheme like A,B,C... AA,AB,... AAA..., similar to converting a number to radix26 I want to implement numbering scheme like Microsoft Word uses for numbering.  first one gets = A,next is  B, next is C, .... then AA, then AB,....and so on.  as shown below   A        B  C  .   .  AA  AB  AC  .  .  AAA  AAB  ....   '=>' here means converted to.  some examples:       1 =&gt; A 26 =&gt; Z 27 =&gt; AA 52 =&gt; AZ 53 =&gt; BA   and heres the code for it:     var convertToNumberingScheme = function(n){         var x = n-1,             r26 = x.toString(26),             baseCharCode = "A".charCodeAt(0);          var arr = r26.split(''),             len = arr.length;          var newArr =arr.map(function(val,i){             val = parseInt(val,26);              if( (i === 0) &amp;&amp; ( len &gt; 1)){                 val = val-1;             }              return String.fromCharCode(baseCharCode + val);         });         return newArr.join('');     }   It seems to work fine, but any ideas if there are some potential bugs or ways to  optimize this. Badge icons missing in Achievements of mobile view The badge icon followed by the site icon in the Achievements dialog is missing in the mobile view. But the same is available in the full site view.  Screenshots for reference:  Achievements - Full site view:        Achievements - Mobile view: How to keep vehicles upgrades equipped in Jetpack Joyride? I have Jetpack Joyride for Android, but every time I start the game I have to equip the magnetic upgrades to all vehicles, except the teleporter, which is the only one already equipped.  I had once a game crash that undid my last 2 magnets purchases, so I ended up with only the teleporter and 20k less in cash. After that, I've bought every vehicle magnet, but still the only one that will remain equipped is the teleport.  Anyone already found some similar bug? How could I fix this, it's kinda annoying have to mannually enable 5 different upgrades every time I want to play.