update is not working
How do I remove a malformed line from my sources.list?
What's the difference between Google Chrome and/or Chromium? What are the advantages/disadvantages to each? I used Google Chrome in Windows, and am now using Chromium in Ubuntu.  Is there any difference to the two programs?  What are the advantages and disadvantages to each program?  Which one seems better? In De Broglie's Explanation for Bohr's Quantization Condition, why do we not use 2πr = n λ/2, why do we use 2πr = n λ? In de Broglie's explanation for Bohr's quantization condition, why do we not use $2\pi r = n\lambda/2$, why do we use $2\pi r = n\lambda$?  We know that in waves on strings, for standing waves creation in a string between two rigid supports, we use "Length of String" $ = n \lambda/2$. Why do we not use a similar concept here? Based on this question: , LVS may be the right solution for my problem.   But when I went to its homepage , I found that LVS has been updated since Nov, 2008. The world's moving fast, and I don't know if LVS was obsolete or not.  Is LVS standing still, or there're some better solutions to replace it?  Thank you so much. What does the dot mean On my reelbox (running Ubuntu) I have found a file in /etc/init that contains the following  # frontpanel-pre - check for frontpanel CAPs and adjust time #  description     "check frontpanel caps"  #start on starting mountall #start on tty-device-added DEVNAME=/dev/ttyS0  task  script         (         /sbin/dev_frontpanel.sh         /sbin/reelfpctl -capability         ) &gt; /dev/.frontpanel.caps         initctl emit --no-wait frontpanel-linked end script   I wonder if the dot in /dev/.frontpanel has some special meaning in linux  I thought the output of the commands in the brackets will be written to a file called ".frontpanel.caps" in /dev/ but there is no such file. In /dev/ there is a frontpanel which is a link to /dev/ttyS0  Could it be, that e.g. echo something &gt; /dev/.frontpanel.caps actually sends data (something in this case) to /dev/frontpanel ?  What does .caps do then? Prove: $\displaystyle\sum_{k=1}^n k k!=(n+1)!-1$ (preferably combinatorially)   It's pretty easy to think of a story for the RHS: arrange $n+1$ people in a row and remove the the option of everyone arranged to height from shortest to highest, but it doesn't hold up for the LHS.   Alternatively, trying to visualize the LHS, I noticed that it's like a right angle tetrahedra:  1  2!+2!  3!+3!+3!  ...  But it doesn't help to see a connection to the RHS.  Note: no integrals or gamma function nor use of other identities without proving them nor generating functions. I use both GNOME and KDE SC. In GNOME, I use Docky but I do not use it with KDE. So, I would like Docky to start up only when I login into GNOME not KDE. In KDE, there is an option to make a program autostart only in KDE. But I cannot find any such option in GNOME.    How can I do this?    Thanks in advance. Difference between $\mathbb C$ and $\mathbb R^2$ What are the basic differences between $\mathbb C$ and $\mathbb R^2$?  The points in these two sets are written as ordered pairs, I mean the structure looks similar to me. So what is the reason to denote these two sets differently? Ampscript date range lookup I want to use LookupOrderedRows and return rows between a start and end date (last month range). What is the best way to handle using Ampscript?   I can add one date to the where using   "DateField", @varStartDate,   But if I add the below to add additional where filters  "DateField", @varStartDate,"DateField", @varEndDate,   I get this error:     "Duplicate Key Field Name: DateField"   EDIT: Also I tried the range as the var for the LookupOrderedRows using   set @strRange = StringToDate(Format(DateDiff(@strStartDate, @strEndDate, "M"),"MM/dd/yyyy"))  and then in the LookupOrderedRows just using  "DateField", @strRange  But that got an error as well. Let $ X \subset \mathbb{R}$ be a non-empty, open set and let $f: X \rightarrow \mathbb{R}$ be a continuous function. Show that the inverse image of an open set is open under f, i.e. show:  If $M \subset \mathbb{R}$ is open, then $f^{-1}(M)$ is open as well.  I think that this should basically follow from the definitions, but I'm still having some troubles with the proof.  Suppose $M \subset \mathbb{R}$ is open, then it follows that $\forall z \in M, \exists r &gt; 0: K_r(z) \subseteq M$  Since f is continuous it follows for each $x_0 \in X$ that for each $\epsilon &gt; 0 ,\exists \delta &gt; 0 : |f(x)-f(x_0)|&lt; \epsilon, \forall x \in X: |x-x_0|&lt;\delta$  Now I need to show that $f^{-1}(M)$ is open, so that for each $z \in M, \exists r&gt;0: K_r(f^{-1}(z_0)) \subseteq f^{-1}(M)$  I'm not sure how to prove this. I guess since $z = f(x)$ and since M is open we have that $\exists r&gt;0:\{z:|z-z_0|&lt;r\}\subseteq M$. And since f is continuous: $|f(x)-f(x_0)| = |z-z_0|&lt; \epsilon$ for all $|x-x_0|&lt;\delta$, but since $|x-x_0|=|f^{-1}(z)-f^{-1}(z_0)|&lt;\delta$ it somehow follows from that that $f^{-1}(M)$ is open?!  Which is just horrible and probably completely wrong. But I'm really confused from all the definitions right now and need some help please. How do I keep Python print from adding newlines or spaces? In python, if I say  print 'h'   I get the letter h and a newline.  If I say   print 'h',   I get the letter h and no newline.  If I say  print 'h', print 'm',   I get the letter h, a space, and the letter m.  How can I prevent Python from printing the space?  The print statements are different iterations of the same loop so I can't just use the + operator. This is sort of a follow-up to a feature request that resulted in obscuring spam / offensive content from 10K-visible answers:   Suggest the same to be done for questions. As of now, spam questions (, ) preserve their titles and content. Suggest to revise the titles to something like     This question was marked as spam or offensive and is therefore not shown   And the text to something like:     This question was marked as spam or offensive and is therefore not shown - you can see the revision history for details".   Where "the revision history" links to the question revision history.    For those interested, here is a link to screen shots of how spam shines through my flagging summary page and is displayed to me when I click the link to one of deleted questions: .  For the sake of precision, flagger having less than 10K rep would see only upper screen shot - the one that lists question titles ("Call giRℒs blah blah &lt;phone number&gt;") - in their  page. Was the significance of Arya's Braavosi coin ever explained? Jaqen H'ghar gives Arya the iron coin, she can apparently give it to any Braavosi and say Valar Morghulis and that gets her where she needs to go, but why?    Where do these coins come from and what do they indicate to a Braavosi? Best resources to learn bash scripting? Which is correct: "__ is different from __" or "__ is different than __"? As someone who learned English later on in life, I was taught that different from is the correct grammar to use: this is different from that. However, it seems these days everyone uses different than instead. I know it's incorrect usage, but does the language evolve if the majority wins?  Edit: Some commented different than is American English and different from is British English, both are OK. IMO, this isn't like color versus colour, though.   Than is used after a comparative adjective, e.g. taller than, whiter than. The word different isn't a comparative adjective, unless used in more different than. Logically, it makes no sense to say different than. Showing that $f$ is identically $0$ on $\mathbb{D}$ Here is the question: Let $f:\mathbb{D}\rightarrow\mathbb{C}$ be an analytic function.  Suppose that there exists $\epsilon&gt;0$ such that for every $\theta$, $|\theta|&lt;\epsilon$, and $\lim_{z\rightarrow e^{i\theta}}f(z)=0$.  Prove that $f$ is identically $0$ on $\mathbb{D}$. My thoughts:  Well, honestly, I am quite stumped here.  I was thinking I could let $f$ be analytic in some other region (can I even do this?), say the lower half plane and suppose $\lim_{z\rightarrow x}f(z)=0$ whenever $-1\leq x\leq1$, by assumption.  Maybe then I could show that $f$ is identically $0$ on the bigger region, and then consider $f$ on the intersection of those two regions, and then ultimately making my way towards using the uniqueness theorem to show what I want... but I am quite stuck on how to do that... any thoughts, suggestions, etc. are greatly appreciated!  Thank you. If a SHA256 hash with high entropy is then hashed with one made from low entropy, is the resulting hash higher/same/lower entropy? If one were to create a SHA256 hash using 256 coin flips converted to hex (which, as I understand it, is as "entro-phized" as one can capture in SHA256) then take that hash as a string, combine that with a hash of the word "cat" and hash the resulting 512 character string, would the resulting hash from that exercise be any less random than our "perfect" hash we began with?  My thinking is the final string would capture the same amount as the original randomness as what we started with because the "extra" entropy can not be captured and is lost. Is this the case and am I thinking about this correctly? Would hashing something with high entropy with something simpler ever cause a lower amount of randomness or does it only go up?  Thanks to anyone who can help explain this a little better. Firefox browser opens but URL is not launched Error: class X is public should be declared in a file named X.java How can I fix a 404 Error when using a PPA or updating my package lists? PPA seems to be constantly offline. Whenever I use sudo apt-get update, this error is shown:  W: Failed to fetch http://ppa.launchpad.net/ 404  Not Found   How do I fix these errors? I am looking for a closed form (ideally expressed as elementary functions) of the function $\exp_n(x) = \sum_{k=0}^n x^k / k!$.  I am already aware of expressing it in terms of the gamma function. Background / Motivation When counting combinations of objects with generating functions, it is useful to be able to express the partial sum $1 + x + \cdots + x^n$ as $\frac{1-x^{n+1}}{1-x}$. For example, to count the number of ways to pick 5 marbles from a bag of blue, red, and green marbles where we pick at most 3 blue marbles and at most 2 red marbles, we can consider the generating function $f(x) = (1+x+x^2+x^3)(1+x+x^2)(1+x+x^2+\cdots)$. By using the partial sum identity, we can express it as $f(x) = \left(\frac{1-x^4}{1-x}\right)\left(\frac{1-x^3}{1-x}\right)\left(\frac{1}{1-x}\right)$.  Simplify, express as simpler product of series, and find the coefficient of the $x^5$ term. I want to be able to do the same for a generating function in the form $g(x) = \exp_{n_1}(x)^{p_1} \exp_{n_2}(x)^{p_2} \cdots \exp_{n_j}(x)^{p_j}$ The easiest way to extract the coefficient of a given term $x^p / p!$ would be to use a similar closed form expression for $\exp_n(x)$ and a similar technique to $f$. Attempted Solutions Differential equation Recall that the way to prove the identity $1+x+x^2+\cdots+x^n = \frac{1-x^{n+1}}{1-x}$ is to define $S = 1 + x + x^2 + \cdots + x^n$ and notice that: $S - Sx = 1 - x^{n+1}$. Likewise, notice that $y(x) = \exp_n(x)$ satisfies $y - y' = x^n/n!$.  Via SAGE, the solution is $y(x) = \frac{c+\Gamma(n+1,x)}{n!}e^x$.  Our initial condition $y(0) = 0$ so $c=0$.  By , $\Gamma(n+1,x) = n! e^{-x} \exp_n(x)$ so we have $y(x) = \exp_n(x)$. Recurrence Relation Notice that $\exp_n(x) = \exp_{n-1}(x) + x^n/n!$. Using the unilateral Z-Transform and related properties, we find that $\mathcal{Z}[\exp_n(x)] = (z e^{x/z})/(z-1)$. Therefore, $\exp_n(x) = \mathcal{Z}^{-1}\left[(z e^{x/z})/(z-1)\right] = \frac{1}{2 \pi i} \oint_C z^n e^{x/z}/(z-1)\;dz$. $(z^n e^{x/z})/(z-1)$ has two singularities: $z = 1$ and $z = 0$.  The point $z = 1$ is a pole of order one with residue $e^x$.  To find the residue at $z = 0$ consider the product $z^n e^{x/z} (-1/(1-z)) = -z^n \left( \sum_{m=0}^\infty x^m z^{-m} / m! \right) \left( \sum_{j=0}^\infty x^j \right)$.  The coefficient of the $z^{-1}$ term is given when $n - m + j = -1$. The residue of the point $z=0$ is then $-\sum_{m,j} x^m / m! = -\sum_{m=n+1}^\infty x^m / m!$. Let $C$ by the positively oriented unit circle centered at the origin.  By Cauchy's Residue Theorem, $\frac{1}{2 \pi i} \oint_C z^n e^{x/z}/(z-1)\;dz = \frac{1}{2 \pi i} 2 \pi i \left(e^x - \sum_{m=n+1}^\infty x^m / m!\right) = \exp_n(x)$. Finite Calculus I've tried to evaluate the sum using finite calculus, but can't seem to make much progress.