How to check for nulls in a deep lambda expression?
Possible pitfalls of using this (extension method based) shorthand
Why does every server I try say it can't connect? I just re-purchased Minecraft (because my old profile stopped working so I bought it) after not playing it for a couple of months. I've added a bunch of servers, but almost every one says "can not connect."  I know its not because the server is not 1.7.2, because I checked that they'd update. It will say "server can't connect" after a long time. I don't know if its me or the servers.  My server screen looks like this (notice the one at the bottom – it's still loading!): Having different horizontally  distributed equations inside an align environment, only lines are numbered, but not individual equations.    How can the left equations be numbered using subequations? See also the question   \documentclass{article} \usepackage{amsmath} \begin{document}   \begin{subequations}     \begin{align}        %\label{a}         a &amp;= a ,&amp;       \label{b}         b &amp;= b ,\\       %\label{c}         c &amp;= c ,&amp;       \label{d}       d &amp;= d .     \end{align}   \end{subequations} \end{document}     The solution should be able to either:    attach a label to the left equations, or modify the labels on the right to read (1a,b) and (1c,d)    I couldn't find anything in the documentation of amsmath or other packages. I am currently wondering about the famous .  Where does it come from mathematically that when you point with your thumb in the direction of the current, your curved fingers will point in the direction of the $B$-field? In other words, which mathematical operation does it come from? Probably it has to do with some vector product or Stokes theorem application, but I am not quite sure about it. How do I perform a redirect to a custom URL after login? I am trying to redirect users to a custom URL after they logged in, but my code doesn't work.  How do I redirect users after they logged in? Let's say we have a Python script my_script.py that does some data processing with Blender. This script accepts some arguments (e.g. arg1 arg2). How can I forward arguments to the script when using it with the CLI?  blender --background --python my_script.py   The only trick I could find was :  echo "arg1 arg2" &gt; my_input.txt &amp;&amp; blender --background --python my_script.py   Is this really the only way to do that?  Update  I found a  on Stack Overflow. What are irreducibles in the ring $R$ of entire functions? Space after LaTeX commands I have a definition:  \newcommand{\arnold}{Arnold Schwarzenegger}   When I refer to it by:  \arnold is a   it is rendered as:   Arnold Schwarzeneggeris a    In order to have a space in front of "is" I would need to write  \arnold\ is a   Is there some other shorter way? When I sum up the sizes of my files, I get one figure. If I run du, I get another figure. If I run du on all the files on my partition, it doesn't match what df claims is used. Why are there so many different figures for the total size of my files? Can't computers add?  Speaking of adding: when I add the “Used” and “Available” columns of df, I don't get the total figure. And that total figure is smaller than the size of my partition. And if I add up my partition sizes I don't get my disk size! What gives? Is there a way to enable commenting adobe PDF? Let $T=\{z:|z|=1 \mathbin{\text{and}} z \in \mathbb C\}$ be the unit circle in the complex plane, considered as a topological group under complex multiplication and the usual topology. Show that every subgroup of $T$ is either dense in $T$ or finite.  How to prove the denseness? Suppose $a_0,a_1,a_2$ satisfy the recurrence $a_n = 3a_{n-1}-3a_{n-2}+a_{n-3}$ for $n\ge3$   Let $c_n=a_{n+1}-a_n$ for $n\ge1$ and $c_0=0$   Find a linear recurrence of degree at most 2 for the sequence $c_0,c_1,c_2,...$  I'm not entirely sure what they are asking for but I think it is asking for a recurrence relation for $c_n$ where the characteristic polynomial has degree at most 2.  I tried finding a closed form for $a_n$ to try and get rid of the $a_n$ in the $c_n$ equation, but I can't figure it out when the initial conditions aren't specified ($a_0,a_1,a_2$)  Any help would be appreciated! How to install Chromium without snap? I just discovered that chromium will only be released as a snap package.  How can I continue to get chromium, without snap? Is this possible without building from source?  Notes:   Please let's keep to the question as stated - not "what do you have against snap?" I'm not asking how to remove snap (I realize that would break Ubuntu)... just how to use chromium as it is now, a deb.     Update  No, this is not a duplicate of that linked question. I don't need to know "why it's a snap". I want to know how to use it without snap.  Right now there is building from source, and some random PPA mentioned below. I hope someone can advise us of trustworthy alternatives. The square roots of different primes are linearly independent over the field of rationals I need to find a way of proving that the square roots of a finite set    of different primes are linearly independent over the field of    rationals.    I've tried to solve the problem using elementary algebra  and also using the theory of field extensions, without success. To  prove linear independence of two primes is easy but then my problems  arise. I would be very thankful for an answer to this question. I can't create an onCheckedChanged listener for my RadioGroup Imported TIF has dark gray background instead of white using QGIS 2.6  I import a TIF file, and expect the import to show an image that has black lines on a white background (with some other colors here and there), as the native windows viewer will see a white background.   The file, 49MB, imports, but   The TIF image has a dark gray background instead of a white background  I can't tell why.   Any hints?  The same thing happens if I import the TIF image into georeference, which is how I discovered this in the first place.  I created/exported the TIF image using PDFCreator (from a print of a PDF to a TIF, using that program).   Within PDFCreator, I chose a TIF export that set the color map to 4096 colors, as the default created a TIF file that was twice as large.  On testing with the default size (16 million colors or some such).... That file imported and showed the background as white.  And I can't tell why, for that, either.   Any hints?  ======== In response to the comment/question by @BradHards:  The TIFFTAG_PHOTOMETRIC is not present in either file.  The gdalinfo for the large file and small file are identical, but for the presence of two extra lines on the file where the white background turns to dark gray.  Each band sets NBITS=4 for Image Structure Metadata: eg:     Band 1 Block=5100x68 Type=Byte, ColorInterp=Red   Image Structure Metadata:     NBITS=4 Band 2 Block=5100x68 Type=Byte, ColorInterp=Green   Image Structure Metadata:     NBITS=4 Band 3 Block=5100x68 Type=Byte, ColorInterp=Blue   Image Structure Metadata:     NBITS=4   Something about the NBITS=4 state turns the background dark gray.  Alternatively, there is some other problem with the PDFCreator export.  These are the full GDALInfo:  Small with dark gray background:   Driver: GTiff/GeoTIFF Files: small file.tif Size is 5100, 6600 Coordinate System is `' Metadata:   TIFFTAG_DATETIME=2015:01:28 16:41:04   TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)   TIFFTAG_SOFTWARE=GPL Ghostscript 9.07   TIFFTAG_XRESOLUTION=600   TIFFTAG_YRESOLUTION=600 Image Structure Metadata:   INTERLEAVE=PIXEL Corner Coordinates: Upper Left  (    0.0,    0.0) Lower Left  (    0.0, 6600.0) Upper Right ( 5100.0,    0.0) Lower Right ( 5100.0, 6600.0) Center      ( 2550.0, 3300.0) Band 1 Block=5100x68 Type=Byte, ColorInterp=Red   Image Structure Metadata:     NBITS=4 Band 2 Block=5100x68 Type=Byte, ColorInterp=Green   Image Structure Metadata:     NBITS=4 Band 3 Block=5100x68 Type=Byte, ColorInterp=Blue   Image Structure Metadata:     NBITS=4   Large with white background   Driver: GTiff/GeoTIFF Files: larger file.tif Size is 5100, 6600 Coordinate System is `' Metadata:   TIFFTAG_DATETIME=2015:01:28 17:07:16   TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)   TIFFTAG_SOFTWARE=GPL Ghostscript 9.07   TIFFTAG_XRESOLUTION=600   TIFFTAG_YRESOLUTION=600 Image Structure Metadata:   INTERLEAVE=PIXEL Corner Coordinates: Upper Left  (    0.0,    0.0) Lower Left  (    0.0, 6600.0) Upper Right ( 5100.0,    0.0) Lower Right ( 5100.0, 6600.0) Center      ( 2550.0, 3300.0) Band 1 Block=5100x68 Type=Byte, ColorInterp=Red Band 2 Block=5100x68 Type=Byte, ColorInterp=Green Band 3 Block=5100x68 Type=Byte, ColorInterp=Blue Relationship between SVD and PCA. How to use SVD to perform PCA? Principal component analysis (PCA) is usually explained via an eigen-decomposition of the covariance matrix. However, it can also be performed via singular value decomposition (SVD) of the data matrix $\mathbf X$. How does it work? What is the connection between these two approaches? What is the relationship between SVD and PCA?  Or in other words, how to use SVD of the data matrix to perform dimensionality reduction? JavaScript YAML Parser I'm using ubuntu 13.10 as htpc. To save some power, i have set it to suspend after 30minutes of inactivity. Before entering suspended state, a popup appears to warn me that computer is about to get put to sleep. This is a little annoyance since it appears when i resume the pc later.   How can i disable this notification for good? Primary question: A common speaking mistake is to exchange syllables of words, saying "It's trace rhyme!" instead of saying "It's race time!", or pronouncing "kickin' chackatory" instead of "chicken cacciatore." Is there an existing name in poetry, linguistics, or English studies for switching syllables of (quasi-)consecutive words? I am not especially interested in the case when switching syllables results in interpretable homonyms or portmanteaus, like in the first example.  Secondary question: if not, what would you call it?  Tertiary question: is there somewhere a (playful?) taxonomy of fruitful or unfruitful lingual aberrations? I posted a question and a couple of respondents asked for the source code. I could only post portions of the code.  If attachments were allowed I could have uploaded a .zip file with the whole application.  Will this be a feature in SO?