var source = new List&lt;string&gt; { "A1", "A2", "B1", "B2" }; var filtered = source.Where(s =&gt; s.StartsWith("A"));  foreach (var s in filtered)     Console.WriteLine(s);    // outputs first A1 and then A2   It seems like  keeps the original order of elements when used on an ordered IEnumerable (such as a List&lt;T&gt; or T[]). Is this always the case? If yes, where is this documented?
I use LINQ to Objects instructions on an ordered array.  Which operations shouldn't I do to be sure the order of the array is not changed?
Indefinite articles used with plural nouns: It was AN amazing TWO DAYS Product and Box Topologies I am having a hard time understanding why the box topology is finer the the product topology. Of course I know that with finite product, the two are the same. With product topology, the basis elements are defined so that the $U_{\alpha}=X_\alpha$ except for finitely many $\alpha$. So how can this topology be contained in the box topology which has only the product of the  $U_{\alpha}$ as basis. I think it should have been the other way round. Am I missing something here? I need help with this because I have been confused over it for a long time. Why does Blender use so much memory for large textures? We, as high school students have been taught that-because Bohr's model of an atom assigns specific orbits for electrons-that it is better than Rutherford's model. But what Rutherford failed to explain was why electrons don't emit EM waves &amp; fall into the nucleus. I don't see how the introduction of 'atomic orbitals' overcame this defect. Can't it still radiate EM waves? Error propagation with asymmetric uncertainties I red the Wikipedia  on error propagation. I get into some trouble when I want to calculate the error propagation in a specific case. I have real numbers $A$ and $B$ with related upper ($\Delta A_u$, $\Delta B_u$) and lower ($\Delta A_l$, $\Delta B_l$) uncertainties. I have two functions calculated as follows: $$F = \sqrt{A^2+B^2}$$ and  $$G = \tan^{-1}\frac{B}{A}$$ What are the related upper and lower errors of $F$ and $G$?  I found general formulae for Gaussian error distributions ($\Delta A_u = \Delta A_l$ and $\Delta B_u = \Delta B_l$), for instance the first formula of the first answer on . Is there a way to generalize that formula for arbitrary distributions with asymmetric errors as in my example? How do I post code in chat? I would like to be able to post code in chat. I know that I can post inline snippets of code by using backticks, but I don't know how to post blocks of code, with the entire chat message formatted as code, and indentation respected. I am aware of . After reading the comments, I found out that I could format in "fixed width", but I can't see a "fixed width" button anywhere. What should I do? Given the sentence:     Most people who live and work near Washington, DC, would have trouble      imagining dinosaurs walking around the area.   Grammatically, what would ‘imaging’ be called in this case? Present participle or gerund or something?  I mean, if it is a present participle, ‘imagining~’ might be a description of the subject. And if it is a gerund, ‘imagining~’ might be an object of the verb phrase of ‘have trouble’. How do they explain this ‘imagining’ after ‘have trouble’? Is there a "null coalescing" operator in JavaScript? $f$ holomorphic on $D\setminus \{0\}$ and takes no values in $(-\infty,0],$ then $0$ removable If $f$ is holomorphic on $D\setminus \{0\}$ and takes no values in $(-\infty,0]$ then $0$ is a removable singularity.   I thought to prove this by elimination, but I can't really tell anything about the behavior of $f$ around $0$. How can one translate the information about the definition of $f$ in semi-open interval $(-\infty,0]$. C# Textreader and TextWriter are the another way to read and write file respectively...      I added a text box and button I called tbUpdate and btUpdate respectively...      In the right hand column, we’ll use three TextBlocks; the first and third as fixed labels (with the values Likeability: and % respectively)...      WorkerSupportsProgress and WorkerSupportsCancellation which hold true/false values that let the backgroundworker report progress or cancel an async progress respectively...   While learning many the many different aspects of development, I have not come across a book or series where the word respectively is not used in explaining an example. Honestly I guess it's implied that we know what it means. To me I always kind of skim over it because I can usually figure out what they're saying through the surrounding context. Can anyone explain this? How to capture Control+D signal? HTML 5 Video stretch Where can I find a free, very quick, and reliable implementation of FFT in C#?  That can be used in a product? Or are there any restrictions? Array with labeling columns In the Monster Manual, gargoyles, golems, helmed horrors, and xorns all enjoy either immunity or resistance to:     bludgeoning, piercing, and slashing damage from nonmagical weapons that aren't adamantine   Is it actually possible to obtain a nonmagical adamantine weapon?   Although the Dungeon Master's Guide describes adamantine armor (p.150) and Daern's instant fortress (p.160) as being made of this metal, and provides an AC for destructible adamantine objects (p.246), there's no mention of adamantine weapons. The creation spell (PH p.229) can produce an adamantine weapon that lasts for a single minute. The true polymorph spell (PH p.283) can't turn a regular weapon into adamantine, but it might be able to  for an hour. The only way to obtain a (somewhat) permanent adamantine weapon in the game seems to be to loot one from drow elves (MM p.127). A PC (perhaps even a drow) with proficiency in smith's tools could presumably craft a nonmagical adamantine sword during downtime at 5gp per day (PH p.187), except that unlike silvered weapons, there's no pricing for adamantine.   It's seeming like mugging an NPC drow is the only by-the-book way to tool up against gargoyles. Smoke Generator does not work When I try to run the smoke simulator in Blender 2.62 I get no smoke at all. When I attempt to render, the only output is a black screen. What am I doing wrong here that is making the smoke simulation not render?  Is it a mistake I made, or a problem with Blender version 2.62? Square of a function with an essential singularity Let $a$ be a point on the complex plane such that the function $f$ has an essential singularity. I am trying to prove that the square of that function also has an essential singularity.  I suppose that it does not have an essential singularity. Then $\exists ;k$ such that $(z-z_0)^{2k}f^2(z)$ differentiable. Then if I could take the square root and preserve the differentiability I would have finised. Can I do that? Determinant of a specially structured matrix ($a$'s on the diagonal, all other entries equal to $b$) I have the following $n\times n$ matrix:  $$A=\begin{bmatrix} a &amp; b &amp; \ldots &amp; b\\ b &amp; a &amp; \ldots &amp; b\\ \vdots &amp; \vdots &amp; \ddots &amp; \vdots\\ b &amp; b &amp; \ldots &amp; a\end{bmatrix}$$  where $0 &lt; b &lt; a$.  I am interested in the expression for the determinant $\det[A]$ in terms of $a$, $b$ and $n$.  This seems like a trivial problem, as the matrix $A$ has such a nice structure, but my linear algebra skills are pretty rusty and I can't figure it out.  Any help would be appreciated. Can sum of a rational number and its reciprocal be an integer?   My brother asked me this question and I was unable to answer it.   The only trivial solutions which I could think of are $1$ and $-1$.  As to what I tried, I am afraid not much. I have never tried to solve such a question, and if someone could point me in the right direction, maybe I could complete it on my own.  Please don't misunderstand my question.   I am looking for a rational number $r$ where $r + \frac{1}{r}$ is an integer. What's the difference between executing a script like this:  ./test.sh  and executing a script like this:  . test.sh?  I tried a simple, two-line script to see if I could find if there was a difference:  #!/bin/bash ls   But both . test.sh and ./test.sh returned the same information.