I don't understand the meaning of this command.  ls ../slc &gt; dates   How does it work?
I tried to rev a file and then pipe it to cat &gt; same_file but it was turning into a blank file.    While I tried rev file.txt | cat &gt; file2.txt &amp;&amp; mv file.txt file2.txt; it worked.    Even rev file.txt | cat &gt;&gt; file.txt; worked.  But when I tried rev file.txt | cat &gt; file.txt it failed.
If $g\circ f$ is injective and $f$ is surjective then $g$ is injective How can you prove that a function has no closed form integral? In the past, I've come across statements  along the lines of &quot;function $f(x)$ has no closed form integral&quot;, which I assume means that there is no combination of the operations:  addition/subtraction multiplication/division raising to powers and roots trigonometric functions exponential functions logarithmic functions  which when differentiated gives the function $f(x)$. I've heard this said about the function $f(x) = x^x$, for example. What sort of techniques are used to prove statements like this? What is this branch of mathematics called?  Merged with &quot;&quot; by : Sometimes we are told that some functions like $\dfrac{\sin(x)}{x}$ don't have an indefinite integral, or that it can't be expressed in term of other simple functions. I wonder how we can prove that kind of assertion? Different and opposing voltage sources? &ndash; Schematic created using   The diagram above, the voltage sources are equal and wired parallel, they would increase the current(2x) flow to the load(R), but what about this case:          Are the two voltage sources in series now? Multiple addresses in JSON-LD Schema.org Programmatically download (seamless) NED tiles? I used to download 1/3 arcsecond elevation geotiffs from extract.cr.usgs.gov using web services.  But a few days ago, that stopped working, probably because USGS reorganized their site.  I tried emailing USGS and haven't heard back yet.    I could, of course, manually download states or degree tiles using the seamless server, but I want to do it programmatically so that users of my trip planner can get elevation data for their region without human intervention.  And SRTM isn't high enough resolution for bicycle/wheelchair trip planning.  Any ideas? Using OpenSUSE leap 15.1 10.2.29-lp151.2.9.1-x86_64 from vendor OpenSUSE (installed)  CREATE TABLE testtab2(     my_id2 INT AUTO_INCREMENT,     name2 VARCHAR(10),     comment2 VARCHAR(20),     PRIMARY KEY (my_id2) );   testtab.txt:  |Roger |hurray   | |George|today    | |Paul  |yesterday| |John  |last year| |Ringo |tomorrow |   LOAD DATA LOCAL INFILE 'testtab.txt' INTO TABLE testtab FIELDS TERMINATED BY '|';   works fine with linenumbers (my_id) 1-5  INSERT INTO testtab (name,comment) VALUES ('Beatles','band');   this gets linenumber (my_id) 8 - should be 6.  If testtab.txt have 8 records and using INSERT INTO 1 record this gets linenr (my_id) 16. This happens in other tables too - one moved from 199 to 256.  Anyone who can solve the problem? Let $A$ be a UFD. Assume that $a,b \in A$ are relatively prime, $c \in A$ and $a | bc$. To prove that $a|c$, is the following approach correct (or do you have to use some type of prime factorization argument)?  By the relatively prime assumption, $\gcd(a,b)$ is a unit. Call that unit $u \in A^{\times}$. Then we can write $u = ax + by$ for some $x,y \in A$. But then, $c = c \cdot u = c(ax+by)=cax+cby$. However, it is clear that $a|cax$ and the fact that $a|bc$ implies $a|cby$. Thus, $a|cax+cby=c$. If p $\equiv$ 3 (mod 4) with p prime, prove -1 is a non-quadratic residue modulo p. If p $\equiv$ 3 (mod 4) with p prime, prove -1 is a non-quadratic residue modulo p.  I suppose this would not be true if p $\equiv$ 1 (modulo 4).  To prove something is a non-square I find to be tricky. It's difficult to see any straightforward way to do this using only the definition of congruence for example. Quick question: what is the compiler flag to allow g++ to spawn multiple instances of itself in order to compile large projects quicker (for example 4 source files at a time for a multi-core CPU)? I am trying to slice up my models using the Boolean modifier.  After applying the modifier on my smooth mesh, I get the expected result, a flat dissection to separate my mesh into two.  The problem lies in how I can resolve the visual "jaggered" edge that separates my (smooth) mesh exterior from the flat dissection face.    Is it possible to achieve a smooth-to-flat variation without this artifact?   I tried to alter a mixture of the two but end up with artifacts, or unwanted blocky flat mesh faces around the dissection edge of my mesh. A result of Stieltjes Integral While studying the Riemann - Stieltjes integral, I read this exercise in my book:  "Let $f:[a, b]\to \mathbb{R}$ be a bounded function. Denoted $L(P, f)$ the lower Darboux sum and $|P|$ the mesh of the partition $P$. Prove that for every $\epsilon&gt;0$, there exists $\delta&gt;0$ such that for every partition $P$ with $|P|&lt;\delta$, we have: $\underline{\int_{a}^{b}}f(x)dx-L(P, f)&lt;\epsilon$."  My question is: Can we generalize this problem for Stieltjes integral, with $\underline{\int_{a}^{b}}f(x)d\alpha$ instead of $\underline{\int_{a}^{b}}f(x)dx$?  Particularly, can we have this theorem?  Let $f:[a, b]\to \mathbb{R}$ be a bounded function and $\alpha$ is a monotonic function on $[a, b]$ . Denoted $L(P, f, \alpha)$ the lower Darboux sum and $|P|$ the mesh of the partition $P$. Prove that for every $\epsilon&gt;0$, there exists $\delta&gt;0$ such that $\underline{\int_{a}^{b}}f(x)d\alpha-L(P, f, \alpha)&lt;\epsilon$ for every partition $P$ with $|P|&lt;\delta$?  I don't know how the mesh of the partition relate to the function $\alpha$. Every Function in a Finite Field is a Polynomial Function A sci-fi book or TV show about a tribesman discovering he or she actually lives in a huge spaceship The story starts with a tribesman going on a exploratory voyage around the land, meeting other progressively more and more distant tribes, learning about the world. Gradually he or she discovers that the "world" is actually a giant spaceship flying through space.  The story climaxes by the hero ascending to the commanding deck and learning who actually pilots the ship and to what purpose. I want to do something like String.Format("[{0}, {1}, {2}]", 1, 2, 3) which returns:  [1, 2, 3]   How do I do this in Python? When I can scroll down far enough to have the hot network questions overlap the footer (because my question is short) there is no background under the text:    Could they either be given a white background: (just disable the transparency option)    Or stop at the footer:      This also happens with the help text on some sites, as per this bug report:     Ubuntu 14.04.1 (Latest LTS Version), . Same problem with  and .  Windows 10 Pro,  and .  (Images linked to screenshot of browser)  My question is different from  because my issue is the lack of background on the footer.   I think there was a site redesign? Clicking on a spoiler tag to reveal the text shouldn't navigate you to another page This is an issue I noticed when reading . On multiple occasions I ended up inadvertently clicking a link that I could not see when I was just trying to reveal the spoiler text.         Can links be deactivated in spoilers until the text is revealed?  (Edit: this issue seems particularly to apply to those using touch screen devices with the "full site" theme) $(a_n+a_{n+1})$ is convergent implies $(a_n/n)$ converges to $0$ Let $(a_n)$ be a sequence such that $(a_n+a_{n+1})$ is convergent. Prove that $(a_n/n)$ converges to $0$.   $(a_n+a_{n+1})$ convergent to $L$ means that for all $\epsilon$, there exists $N$ such that for all $n\geq N$, $|L-a_n-a_{n+1}|&lt;\epsilon$, or in other words $L-\epsilon&lt;a_n+a_{n+1}&lt;L+\epsilon$. How to proceed from here? Reflectivity of a glowing-hot metal surface When a polished piece of metal (or steel in particular) is heated to incandescence, how do its reflective properties change?  Given a mirror-like surface, would the object temporarily cease to act like a mirror at a certain temperature?  Would the specular reflection of light turn into diffuse reflection; in other words, would the surface temporarily become matte/dull?  I am not asking about permanent changes to the object such as melting, but rather can there be a temporary change in the reflectivity only while the the object is hot, that disappears when the object is cooled down?  Background of the question: I have a laser scanner that usually has trouble scanning shiny surfaces with high specular/ low diffuse reflectivity; and it seems to work a lot better for hot steel pieces than for cold ones. Glowing steel also looks less shiny to me than cold steel, but of course that is hard to tell with all the glowing Help finding the limit of $\lim_{n \to \infty}\prod_{k=1}^{n}\left(1+\frac{1}{n}f\left(\frac{k}{n}\right)\right)$. Cycles not rendering image or movie clip used as background in the viewport First time I've used cycles rendering engine.  I'm using a movie clip as the background in short animation. Selected RBGA under Property Tab, and Transparent under Film Tab.  It looks good and individual frames in OpenGL active viewport render, and looks fine.  When I try to get it to spit out PNG files of the finished animation the objects render out fine, except no movie clip background as Blender Render engine did when using Paper Sky setting.  Operator error, or am I trying to do something Cycles won't do?  Haven't found an answer in my searches so far.  Can anyone point me in the right direction please.   Addition:  I think I found my problem after a couple more hours of research.  Post should read "operator ignorance" instead of operator error.  Too tired to try the solution tonight, everything looks better in the morning. Thanks anyway.  Sorry, I just saw your posts.  Really tired.  Much appreciation.