apt-get update meaning of 1st. column of output
What does 'Ign' , `Get` or 'Hit' mean when running an apt-get update?
How can I find the method that called the current method? When logging in C#, how can I learn the name of the method that called the current method? I know all about System.Reflection.MethodBase.GetCurrentMethod(), but I want to go one step beneath this in the stack trace. I've considered parsing the stack trace, but I am hoping to find a cleaner more explicit way, something like Assembly.GetCallingAssembly() but for methods. Books about matroids Could you recommend any approachable books/papers/texts about matroids (maybe a chapter from somewhere)? The ideal reference would contain multiple examples, present some intuitions and keep formalism to a necessary minimum.  I would appreciate any hints or appropriate sources. Found the alternative form: $\sum _{k=1}^\infty ((1-\frac{1}{k})^{k})^k$. Tried various criteria, no luck so far. Clocks for multiple timezones in GNOME Shell I looked everywhere but I couldn't find a way to display multiple clocks in GNOME 3. In classic GNOME and Unity, it is possible. Also, for some strange reason, additional timezones cannot be added to the clock using the time-date applet in classic GNOME. Any solutions? Is there a way to add a timer to a Beamer presentation? Why didn't mastery of the Elder Wand move on from Harry? There's a lot of emphasis on Harry becoming the master of the Elder Wand after he defeats Draco. But what constitutes a “defeat”?  It seems that Harry wins a wrestling match with Draco, so now he’s the master of the Elder Wand.  But lots of other stuff happens to Harry: Nagini almost kills him, and he escapes just in time, but his wand breaks. The Snatchers chase him through the forest. He and his friends practically surrender (and Hermione even tries to disguise Harry). Voldemort almost kills Harry in the Forbidden Forest (or actually does, depending on how you look at it).  Why are none of these considered to be “defeats”? In Spivak's Calculus 3rd Edition, there is an exercise to prove the following:  $$x^n - y^n = (x-y)(x^{n-1} + x^{n-2} y + ... + x y^{n-2} + y^{n-1})$$  I can't seem to get the answer. Either I've gone wrong somewhere, I'm overlooking something, or both. Here's my (non) proof:  $$\begin{align*} x^n - y^n &amp;= (x - y)(x^{n-1} + x^{n-2}y +\cdots+ xy^{n-2} + y^{n-1}) \\           &amp;= x \cdot x^{n-1} + x \cdot x^{n-2} \cdot y + \cdots + x \cdot x \cdot y^{n-2} + x \cdot y^{n-1}\\ &amp;\qquad + (-y) \cdot x^{n-1} + (-y) \cdot x^{n-2} \cdot y + \cdots + (-y) \cdot x \cdot y^{n-2} + (-y) \cdot y^{n-1}\\           &amp;= x^n + x^{n-1} y + \cdots + x^2 y^{n-2} + x y^{n-1} - x^{n-1}y - y^2 x^{n-2}  - \cdots- x y^{n-1} - y^n \\           &amp;= x^n + x^2 y^{n-2} - x^{n-2} y^2 - y^n  \\           &amp;\neq x^n - y^n \end{align*}$$  Is there something I can do with $x^n + x^2 y^{n-2} - x^{n-2} y^2 - y^n$ that I'm not seeing, or did I make a mistake early on?  EDIT:  I should have pointed out that this exercise is meant to be done using nine of the twelve basic properties of numbers that Spivak outlines in his book:     Associate law for addition   Existence of an additive identity   Existence of additive inverses   Commutative law for additions   Associative law for multiplication   Existence of a multiplicative identity   Existence of multiplicative inverses   Commutative law for multiplication   Distibutive law How to force nginx to resolve DNS (of a dynamic hostname) everytime when doing proxy_pass? Some websites have code to "break out" of IFRAME enclosures, meaning that if a page A is loaded as an IFRAME inside an parent page P some Javascript in A redirects the outer window to A.  Typically this Javascript looks something like this:  &lt;script type="text/javascript"&gt;   if (top.location.href != self.location.href)      top.location.href = self.location.href; &lt;/script&gt;   My question is: As the author of the parent page P and not being the author of the inner page A, how can I prevent A from doing this break-out?  P.S. It seems to me like it ought to be a cross-site security violation, but it isn't. Proof on showing if F(x,y,z)=0 then product of partial derivatives (evaluated at an assigned coordinate) is -1 The task is as follows:     Given: $$F(x,y,z) = 0$$    Goal:  Show    $\frac{\partial  z}{\partial y}|_x \frac{\partial  y}{\partial x}|_z \frac{\partial x}{\partial z} |_y = -1$   Here is my work so far:  (1) Differentiate with respect to y, I get:  $0 + F_2 + F_3  \frac{\partial z}{\partial y} = 0$  So $ F_3  \frac{\partial z}{\partial y} = - F_2$  (2) Differentiate with respect to x, I get:  $F_1 + F_2 \frac{\partial y}{\partial x}  + 0 = 0$  So $ F_2  \frac{\partial y}{\partial x} = - F_1$  (3) Differentiate with respect to z, I get:  $F_1  \frac{\partial x}{\partial z}    + 0  + F_3 = 0$  So $ F_1  \frac{\partial x}{\partial z} = - F_3$  (4) After some manipulations with the $F_i$, I get to the conclusion that $\frac{\partial z}{\partial y}* \frac{\partial y}{\partial x} * \frac{\partial x}{\partial z}  = -1$, so when evaluated with x, z, y respectively, conclusion is still true  My questions are:  (1) Is my proof correct?  (2) For example, when I differentiate with respect to y, I "let" $F_1$ be 0 and find partials for other coordinates.    I had a hard time trying to explain to my friend on the reason(s) why I can do such "let be 0" thing.  Although I think if I can't do that, then there is no way that I can reach the conclusion, but I somehow feel confused about the fact too.  Since my book is doing it that way, my understanding is that I can do such "let be 0" thing based on the independece of x with respect to y, when I differentiate with respect to y.  But is my thought ok?  Would someone please help me on this question? Thank you very much ^_^ I would like to create a String.replaceAll() method in JavaScript and I'm thinking that using a regex would be most terse way to do it.  However, I can't figure out how to pass a variable in to a regex.  I can do this already which will replace all the instances of "B" with "A".  "ABABAB".replace(/B/g, "A");   But I want to do something like this:  String.prototype.replaceAll = function(replaceThis, withThis) {     this.replace(/replaceThis/g, withThis); };   But obviously this will only replace the text "replaceThis"...so how do I pass this variable in to my regex string? Summarize the mathematical problem at the heart of breaking a Curve25519 public key It's pretty easy to generate a Curve25519 private key: generate 32 random bytes of data and then do:  e[0] &amp;= 248 e[31] &amp;= 127 e[31] |= 64   You can then generate a public key by doing  on the private key. For example, here's a random keypair I just generated:  public: e40ed268dff20db8497d0691421d00b086aad1efedcd5bd223d9eb6c0b85665f secret: e3c0e8b20ba7894882ddb37522dbe90867befcf9f31a5ce29c0d7997e0bd856d   The whole safety of public key encryption is that it is hard to take a public key and reverse the operation. Elliptic curve cryptography, as I understand it, relies on the fact that a  is hard to find. In particular, for a given large b and g, it is hard to find an integer k such that  $b^k = g$  How does that equation relate to Curve25519? Specifically, if I had a public key like the one above, how would I express, in math terms, the problem I need to solve to find the private key? How does it relate to the equation I see from time to time - $y^2 = x^3+486662x^2+x$, and the number $2^{255} - 19$?  I am guessing it is not as simple as "the private key is k and the public key is b and/or g" in the equation above. I'm also a little confused because the keys would appear to have roughly the same number of digits, which would seem to imply that there aren't many feasible values for k? I've created main SELECT statement like below. For every row in Base table (base on IDKey I've added columns with values from result of INNER JOIN of few tables.  SELECT   IDKey,    Name,    (select Amount from Table1 INNER JOIN Table2 ... where ID=IDKey) AS AmountTypeX,    (select Amount from Table1 INNER JOIN Table2 ... where ID=IDKey) AS AmountTypeY FROM BaseTable   BaseTable:  IDKey Name  ---------- 1     Ian 2     John 3     Ann ...   INNER JOIN of few tables Table1, Table2... :   ID Amount Type -------------- 1  100    X 1  200    Y 2  300    X 2  400    Y 3  500    X 3  600    Y ...   Result looks like:  IDKey  Name  AmountTypeX  AmountTypeY ------------------------------------- 1      Ian   100          200 2      John  300          400 3      Ann   500          600 ...   Do you have any suggestion how to avoid this nested SELECT statements in the main query at the begining and made this query simpler and more effective ?  I wast thinking about PIVOTING of the INNER JOIN result to look like below (all data for particular ID in one row) and then JOIN with main query but Have no idea how to do this and is it possible.  ID  X   Y ----------- 1   100 200 2   300 400 3   500 600 ... Show that $d_2$ defined by $d_2(x,y)=\frac{|x-y|}{1+|x-y|}$ is a metric I am pretty sure that this is such a stupid, stupid question, but how do you prove that $d_2(x,y)={|x-y|\over {1+|x-y|}}$ satisfying the third condition to be a metric, which is the triangle inequality.   I know that I should really be able to do this, but I just can't, I keep seeing a contradiction. Please help me. I need to prove that $K\subseteq \mathbb{R}^n$ is a compact space iff every continuous function  in $K$ is bounded.  One direction is obvious because of Weierstrass theorem. How can i prove the other direction? I tried to assume the opposite but it didn't work for me.  Thanks a lot. The Safari app has disappeared from my iPhone? I can't find the safari icon on my iphone 4?  I have tried resetting home screen layout and that doesn't work.  My restrictions button is 'on' and it asks for a password for this button.  I don't have a password.  Can you help? Thanks, Is a time series the same as a stochastic process? A stochastic process is a process that evolves over time, so is it really a fancier way of saying "time series"? Closed-loop function question How do I find the   How do I find the transfer function of Gd(s)?  I am able to find the transfer function of Gr(s) but I am not really sure about Gd(s)? and how do i determine which order is this closed system? every rank 2 oriented matroid is realizable What are integers $x$ and $n$ such as $ x^4+x^3+x^2+x+1 = n^2$? What are the integer numbers $x$ such as $x^4+x^3+x^2+x+1$ is the square of an integer?  $0$ and $-1$ are obvious answers, but how many are there?