How do I de-interlace a list in python
How do you split a list into evenly sized chunks?
In formal logic, how is it possible for an argument with a contradictory conclusion to be valid? I've recently been trying to introduce myself to formal logic, and I've hit a stumbling point:  In the text I'm reading, a valid argument is defined as "an argument in which it is impossible for the premises to be true and at the same time the conclusion false."  The text then later prompts me to declare whether it's possible for an argument to be valid with a contradiction for a conclusion. The answer key then claims that yes, it is in fact possible, but offers no further explanation. I'm also supposed to create an example.  I just can't wrap my head around this one.  Here's the example I've worked up, is this a valid argument?   If grass is green then it is raining.  If water is wet then it is not raining.  Therefore: It is raining and not raining.   My head hurts. Why is saltatory conduction in myelinated axons faster than continuous conduction in unmyelinated axons? How to prove that the ideal $I=(x^3-y^2)$ in $k[x,y]$ is prime?    I have constructed a map from $k[x,y]$ to $k[t]$, which maps $x$ to $t^2$, and $y$ to $t^3$. Then, I want to show that the kernel is exactly $I$. But the difficulty is that how to prove the kernel is contained in $I$.  Could you help me? Thanks a lot! If $2^n+1$ is prime, why must $n$ be a power of $2$? A little bird told me that if $2^n+1$ is prime, then $n$ is a power of $2$. I tend not to trust talking birds, so I'm trying to verify that statement independently.  Suppose $n$ is not a power of $2$. Then $n = a \cdot 2^m$ for some $a$ not a power of $2$ and some integer $m$. This gives $2^n+1 = 2^{a \cdot 2^m}+1$. Now I suspect there's a way to factor that, but I don't see how. Can someone give me a hint? Extra Backslash Required in First Appended Newline in sed Currently, a user does not get any notification when a trivial edit (less than 6 characters, by a user who has the ) is made on one of his/her posts. As in .  Even though the user is trust-worthy (owing to the rep of the user), wouldn't it be nice for the OP to get a notification whenever an edit is made, even trivial? pgrouting unexpected output The reasoning my book uses is as follows:   Since $(3+i)(3-i) = 10$, $10 + \langle 3+i\rangle = 0 + \langle 3+i\rangle $. Also, $i + \langle 3+i\rangle = -3 + \langle 3+i\rangle = 7 + \langle 3+i\rangle$. So, $\mathbb{Z}[i]/\langle 3+i\rangle = \{k + \langle 3+i\rangle \mid k = 0,1,\ldots ,9\}$, since $1 + \langle3+i\rangle$ has additive order $10$.   I do not understand why the additive order of $1 + \langle 3+i\rangle$ is $10$, or why the fact that $(3+i)(3-i) = 10$, shows the additive order or $1 + \langle 3+i\rangle$  is $10$. If someone could please explain this I would greatly appreciate it.   Note: I apologize for not using MathJax to write this post. I intend to learn it over the coming weekend. What is the difference between Θ(n) and O(n)? I've got a development webserver on an Ubuntu box inside of VMWare Workstation 7.1.3. I'd like to run a web browser on a Windows machine (the host OS) for actually testing a web page I'm working on -- hard to run IE tests in Ubuntu :)  However, if I simply try to ping the IP given to the ubuntu VM (192.168.83.137) (or open it in my browser for that matter), it seems the host cannot communicate with the guest.  How do I allow the guest OS to communicate with the host when the guest is running in NAT mode? I lost control of my account before registering, can it be recovered? meaning of -h in ls command Rename Multiple files in unix I have multiple files whose names look like this  2313_ABCDEAUG2014_PQRST_0_.pdf 3244_ABCDEAUG2014_PQRST_0_.pdf 4234_ABCDEAUG2014_PQRST_0_.pdf   t want to rename the file in the following format.  AZ-2014-08-2313.pdf AZ-2014-08-3244.pdf   Please suggest. Does installing and using Wine open up your Linux platform to Windows viruses? Prove the following inequality:   $$\dfrac{e^x + e^{-x}}2 \le e^{\frac{x^2}{2}}$$   This should be solved using Taylor series.  I tried expanding the left to the 5th degree and the right site to the 3rd degree, but it didn't help.  Any tips? I'm looking for an easy and robust way to strip all the comments from a listing. My approach (passing \@gobble to the commentstyle key) correctly removes all the one-line comments and block comments. However, the white space left behind by by block comments remains, creating useless gaps in my listing. See the screenshot below (the red rectangle is my emphasis). Any idea?    \documentclass{article}  \usepackage{xcolor} \usepackage[T1]{fontenc} \renewcommand{\ttdefault}{pcr} \usepackage{listings}  \makeatletter \lstset% {%   basicstyle   = \ttfamily,   morecomment  = [l]{//},   morecomment  = [s]{/*}{*/},   frame        = single,   commentstyle = \itshape\color[gray]{.5},   rulecolor    = \color{black},   breaklines, } \makeatother  \usepackage{filecontents} \begin{filecontents*}{sample.c} #include &lt;stdio.h&gt;  /*  block comment taking up white space */ main() {     float fahr, celsius;     float lower, upper, step;     lower   = 0;    /* lower limit of temperature scale */     upper   = 300;  /* upper limit */     step    = 20;   /* step size */     celsius = lower;     printf("\nCelsius\tFahr\n");     while (celsius &lt;= upper)        {         fahr = (9.0/5.0) * celsius+32.0;         printf("%3.0f\t%6.1f\n", celsius, fahr);         celsius = celsius + step;     } } \end{filecontents*}  \begin{document} \makeatletter \lstinputlisting[caption={with comments}]{sample.c} \lstinputlisting[caption={without comments},commentstyle={\@gobble}]{sample.c} \makeatother \end{document} Note: I cannot specificly tell which version of which of the two conflicting packages fixed the issue, but as of 2016 mathpec and polyglossia no longer show the issue.   Basically, I have encountered the same error as  and the workaround suggested by Andrey Vihrov reenables me to compile the document. The problem now is, that any shorthand defined by the ngerman-package (most notably the non-breaking hypen "~) has now been disabled, and I see combinations of american style closing quotes followed by a non-break space where a non-breaking hyphen should be.  Is there any way possible of keeping the shorthand definition, or redefining it to something else (something like \nbhy pops up to mind)?  I am using XeLaTeX as supplied by TeXLive. Nested cross validation for model selection How can one use nested cross validation for model selection?   From what I read online, nested CV works as follows:   There is the inner CV loop, where we may conduct a grid search (e.g. running K-fold for every available model, e.g. combination of hyperparameters/features) There is the outer CV loop, where we measure the performance of the model that won in the inner fold, on a separate external fold.    At the end of this process we end up with $K$ models ($K$ being the number of folds in the outer loop). These models are the ones that won in the grid search within the inner CV, and they are likely different (e.g. SVMs with different kernels, trained with possibly different features, depending on the grid search).  How do I choose a model from this output? It looks to me that selecting the best model out of those $K$ winning models would not be a fair comparison since each model was trained and tested on different parts of the dataset.  So how can I use nested  CV for model selection?   Also I have read threads discussing how nested model selection is useful for analyzing the learning procedure. What types of analysis /checks can I do with the scores that I get from the outer K folds? How to download all required Ubuntu drivers Migrated question's answers can be upvoted twice by the same user