Macbook Pro can only startup with external hard drive connected
Macbook Pro hard drive failing?
Any hard-working student is a counterexample to "all students are lazy".  What are some simple counterexamples to "if random variables $X$ and $Y$ are uncorrelated then they are independent"? Polynomial ring $R[X] $ has zero Jacobson radical, for $R$ a domain Mutable vs immutable objects I'm trying to get my head around mutable vs immutable objects. Using mutable objects gets a lot of bad press (e.g. returning an array of strings from a method) but I'm having trouble understanding what the negative impacts are of this. What are the best practices around using mutable objects? Should you avoid them whenever possible? I was trying to think but cannot figure it out. For instance, if the interaction is small, for instance limited to a windows, the observers in each universe will see that the other goes in reverse. But what if they can start a more meaningful interaction? (for instance, if one observer crosses the window and moves to the other universe, will anything change? why and how fast? (at least at the beginning his thinking will move in the same time arrow than in his universe, but the physical processes around him will still violate the second law? Prove that $ S=\{0\}\cup\left(\bigcup_{n=0}^{\infty} \{\frac{1}{n}\}\right)$ is a compact set in $\mathbb{R}$. Prove that $ S=\{0\}\cup\left(\bigcup_{n=0}^{\infty} \{\frac{1}{n}\}\right)$ is a compact set in $\mathbb{R}$, but $\bigcup_{n=0}^{\infty} \{\frac{1}{n}\}$ is not a compact set.   (Can we use definition of compact set for this problem? ) I want to switch to French locale. So I tried the below command:  myUbundu@myUbundu-desktop:~$ export LC_ALL=fr_FR   But I am getting the warning  -bash: warning: setlocale: LC_ALL: cannot change locale (fr_FR)   How to set the locale to French? Do I need to install additional packages? Is transferring to another university an option for an unhappy PhD student? Can I award user with special bounty after accepting his anwer? I have a , and I haven't start a bounty for this question. After I got my answer I'd like to give a user a special bounty, because I consider his answer very helpful and it saved me a lot of time. I've already accepted the answer. Is there a way how can I give him some bounty?  Thank you A Riemann integrable function must have infinitely many points of continuity How do I stop Outlook Out-Of-Office from replying to certain addresses? When I am out of the office, if I turn Out-of-Office on, it auto-replies to the automated emails I get from our Bug Tracking system, which leads to our Bug Tracking system getting full of message about my holiday.  With Outlook Out-of-Office, how do I set it to not respond to certain 'From' addresses? I see its something to do with the optional Rules in the O-o-O dialog, but its not that clear how to stop it from replying using the rules.  I'm on Outlook 2003 and Exchange 2003 but advice for any version will probably be useful to people. Best way to run scheduled tasks Today we have built a console application for running the scheduled tasks for our ASP.NET website. But I think this approach is a bit error prone and difficult to maintain. How do you execute your scheduled task (in an windows/IIS/ASP.NET environment)  Update:   Examples of tasks:   Sending email from an email-queue in the database Removing outdated objects from the database Retrieving stats from Google AdWords and fill a table in the database. How to connect to Salesforce REST API without OAuth? How does Jitterbit do it? Enumerations on PHP I know that PHP doesn't yet have native Enumerations. But I have become accustomed to them from the Java world. I would love to use enums as a way to give predefined values which IDEs' auto-completion features could understand. Constants do the trick, but there's the namespace collision problem and (or actually because) they're global. Arrays don't have the namespace problem, but they're too vague, they can be overwritten at runtime and IDEs rarely know how to autofill their keys without additional static analysis annotations or attributes. Are there any solutions/workarounds you commonly use? Does anyone recall whether the PHP guys have had any thoughts or decisions around enumerations? If $R$ is a local ring and $M$ and $N$ are finitely generated $R$-modules such that $M\otimes N=0$ then how does it follow from Nakayama's lemma that either $M=0$ or $N=0$?    This is an exercise in Atiyah and Macdonald. The part I could not show in the hints is $({M{\otimes}_R N)}_{k}=0$ implies $M_{k}{\otimes }_{k} N_{k}=0$, where $k=R/\mathfrak m$ and $\mathfrak m$ is the maximal ideal of $R$. Understanding the differential $dx$ when doing $u$-substitution What exactly is a photon? Consider the question, .  The answers say, "an elementary particle" and not much else. They don't actually answer the question. Moreover, the question is flagged as a duplicate of,  &ndash; the answers there don't tell me what a photon is either. Nor do any of the answers to  mentioned in the comments. When I search on , I can't find anything useful. Questions such as,  look promising, but bear no fruit.  say things like, "the photon is an excitation of the photon field." That tells me  nothing. Nor does the , which says:     The photon is the quantum of the electromagnetic four-potential, and therefore the massless bosonic particle associated with the electromagnetic force, commonly also called the 'particle of light'...   I'd say that's less than helpful because it gives the impression that photons are forever popping into existence and flying back and forth exerting force. This same concept is in the  too - but it isn't true. As , "Virtual particles only exist in the mathematics of the model." So, who can tell me what a real photon is, or refer me to some kind of authoritative informative definition that is accepted and trusted by particle physicists? I say all this because I think it's of paramount importance. If we have no clear idea of what a photon actually is, we lack foundation. It's like what :     Photons seem to be one of the foundation ideas of quantum mechanics, so I am concerned that without a clear definition or set of concrete examples, the basis for understanding quantum experiments is a little fuzzy.   I second that, only more so. How can we understand pair production if we don't understand what the photon is? Or the electron? Or the electromagnetic field? Or everything else? It all starts with the photon.   I will give a 400-point bounty to the least-worst answer to the question. One answer will get the bounty, even if I don't like it. And the question is this:    What exactly is a photon? Where did the world go? I was playing on my main world when my laptop ran out of power.  I found a charger and woke it up, but Minecraft had crashed.  Now, it doesn't appear in the world selection screen!  I have verified that it still exists in the Minecraft folder, and the directory contents look to be in order.  Does Minecraft save an internal flag somewhere when it crashes hard?  If so, how do I reset it? How do we compare the size of numbers that are around the size of Graham's number or larger? When numbers get as large as Graham's number, or somewhere around the point where we can't write them as numerical values, how do we compare them?  For example:  $$G&gt;S^{S^{S^{\dots}}}$$  Where $G$ is Graham's number and $S^{S^{S^{\dots}}}$ is $S$ raised to itself $S$ times and $S$ is Skewes number.  It appears obvious (I think) that Graham's number is indeed larger, but how does one go about proving that if both numbers are "so large" that they become hard to compare?  More generally, how do we compare numbers of this general size?  As a much harder problem than the above, imagine a function $G(x,y)$ where $G(64,3)=$ Graham's number.  The function $G(x,y)$ is as follows:  $$G(x,y)=y\uparrow^{(G(x-1,y))}y$$  Where $G(0,y)$ is given.  I ask to compare $G(60,S)$ and $G(64,3)$ I happen, time and again, to read and hear people – among which people working in cinema – regretting the fact that film (in the sense of actual reels of plastic strip) is nowadays very rarely used when shooting movies. Is there some ground to such nostalgia?  Of course I am not looking for opinions for or against film vs. digital media, but sourced, objective reasons. Is there anything that could be done with film but not with digital supports? Are there measurable differences in effects on viewers? Suppose that $f:M \to N$ is a smooth map of two manifolds and $E$ is a vector bundle over $N$. Given a connecton $\nabla$ on $E$ one can pull it back to $f^*N$ (which is a bundle over $M$) and obtain a connection $f^* \nabla$.   If $E=TN$ is a tangent bundle one can consider the Levi-Civita connection $\nabla$, with respect to the chosen metric $g$ on $N$. It is characterised uniquely as torsion free metric connection. Given a map $f:M \to N$ one can pullback the metric $g$ to $f^*g$. If it happens that $f^*g$ is again a metric (which is the case for example for immersions) one can consider the Levi Civita connection on $M$ with respect to $f^*g$. I wonder how these two constructions are related, in particular      Is there a way to pullback affine connections to get again affine connection (i.e. connections on tangent bundle)?     Additionally I would like to know:     What is the relation between Christoffels symbols for the connection and for its pullback?