I installed Linux on a partition and now I don't know how to boot it
How can I repair grub? (How to get Ubuntu back after installing Windows?)
Calculating the total number of surjective functions Homeomorphism that maps given points to given points Why is learning modern algebraic geometry so complicated? What would you call a word that doesn't exist in or translate well into another language? I know that taking the derivative of position with respect to time defines what we call velocity, but I've never heard of physicist going in the opposite direction with position. Is there any application for the integral of position with respect to time?  Maybe with respect to something else? "a ten years old boy" or "a ten year old boy" 1) a ten years old boy is sitting on the couch.      2) a ten year old boy is sitting on the couch.      3) a ten-years old boy is sitting on the couch.      4) a ten-year old boy is sitting on the couch.   Which is correct? Best way to parse RSS/Atom feeds with PHP I'm currently using  but it sometimes falls over when the RSS or Atom feed isn't well formed. Are there any other options for parsing RSS and Atom feeds with PHP? "There are a good many scholars ..." is it right? In "Seeing like a state" of James C.Scott there is a sentence at the beginning of a paragraph (Acknowledgements xi):     There are a good many scholars whose writings opened up new   perspectives for me or provided outstanding analyses of issues that I   could not have hoped to study so comprehensively on my own.   What worries me is a good many scholars. Is this some type of inversion or ancient English? Is this grammatically right? Why is a here? I thought that appropriate version would be There are many good scholars. Am I wrong? FileZilla: How to copy files from one directory to another on the same server? I want to copy files from one directory to another on the same server using FileZilla. Please guide me how can it be done? This code always works, even in different browsers:  function fooCheck() {   alert(internalFoo()); // We are using internalFoo() here...    return internalFoo(); // And here, even though it has not been defined...    function internalFoo() { return true; } //...until here! }  fooCheck();   I could not find a single reference to why it should work, though. I first saw this in John Resig's presentation note, but it was only mentioned. There's no explanation there or anywhere for that matter.  Could someone please enlighten me? System log full of session and slice messages If $a \cdot a = 1$ then $a = 1$ or $a = -1$ Let $F$ be a field.   And let $a \in F$ such that $a \cdot a = 1$.  Claim: $a = 1$ or $ a = -1$  Before, I begin with the proof I cannot understand what $ a = -1$ represents...  Is $a = -1$ representing the inverse of $a$?   I am capable of getting to $a = 1$ with no trouble, but how do you get the $-$ sign to show up in your proof?   Proof: This is my attempt at getting to $a=-1$.  If $a = 0$ then we have $0 \cdot 0 = 0 \neq 1$. Then this implies that $a \neq 0$ which implies that $ \exists b \in F,$ s.t. $a \cdot b = 1$, i.e. $b$ is the multiplicative inverse of $a$.  Knowing this fact prove as follows...:  $a \cdot a = 1 \implies$ $ (a \cdot a) \cdot b = 1 \cdot b \implies$ $a \cdot (a \cdot b) = 1 \cdot b \implies$ $a \cdot 1 = 1 \cdot b \implies$ $ 1 \cdot a =1 \cdot b \implies$ $a = b$.   But since $b$ is the multiplicative inverse of $a$ is this enough to say that $a = -1$? Can I just change straightforward wheel axles to QR skewers? Appending the same string to a list of strings in Python If a lens focuses all incoming light to a point, how do we get 2D images? How do lenses produce 2-dimensional images, if a lens bends all incoming rays of light to intersect at the focal point? Shouldn't this produce a single dot of light on a screen placed at the focal length?  This is basically the standard diagram that always shows up in textbooks:    I know this doesn't happen in real life--I used to use telescopes pretty frequently for work. The most in-focus image would be the one with the smallest diameters for the stars, which, of course, we think of point sources at infinity. But--the light from all stars (despite being at infinity) is not all focused at a single point. Instead, each star's light is focused at its own $(x,y)$ point on a 2D image.  I can't reconcile the theory as I understand it with any of my real-life experience with optics. What am I missing? Why is this markdown for a link not showing properly? The Stack Exchange (Personal Productivity) markdown  is showing literally rather than as a named link. Don't know why. Black body radiation and spectra lines My understanding was that all objects emit light of continuous spectrum when hot ( black body radiation) but then you see discreet wavelengths in spectra lines and I am confused. I know I am making a mistake somewhere but not able to point it Trying to understand what is a p value I am trying to understand what a p value is and what is its importance in statistics, from this example.  For $50$ specimens of alloy steel the rock hardness scale measured an average of $62$ with standard deviation $8$ he manufacturer claims that the alloy has average strength of $64$ at significance of $0.01$ can you refute this?  Well I did this problem and saw no at this level you cant refute it , I use the null being that the hardness was $64$ and the alternate that the hardness was less then $64$. From the data we observe a $z=-1.7677$ but the chart is $z=-2.33$ and so we cant refute null at this level.  But now I want to understand what the p value would be ,  I thought it was that the p-value is the probability of getting the observed value of the test or a value with even more evidence against the null if the null is actually true. So using that I just look on the z chart, the probability of seeing Z greater then $1.7677$ is $0.0384$, so is that the p value? If $A,B,C$ are the angle of a triangle, then show that $\sin A+\sin B-\cos C\le \dfrac32$ I tried substituting $C=180^\circ-(A+B)$ and got stuck. I also tried using the formula $\sin A+\sin B=2\sin \frac{A+B}{2}\cos \frac{A-B}{2}$ without any progress. Please help! I am trying to automate various tasks in ArcGIS Desktop (using ArcMap generally) with Python, and I keep needing a way to add a shapefile to the current map. (And then do stuff to it, but that's another story).  The best I can do so far is to add a layer file to the current map, using the following ("addLayer" is a layer file object):  def AddLayerFromLayerFile(addLayer):  import arcpy  mxd = arcpy.mapping.MapDocument("CURRENT")  df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]  arcpy.mapping.AddLayer(df, addLayer, "AUTO_ARRANGE")  arcpy.RefreshActiveView()  arcpy.RefreshTOC()  del mxd, df, addLayer   However, my raw data is always going be shapefiles, so I need to be able to open them. (Equivalently: convert a shapefile to a layer file without opening it, but I'd prefer not to do that).