Traveling Amsterdam-Brussels with KLM ticket on Thalys - When / where does my ticket get stamped?
Can I skip my train leg booked with a KLM flight?
To install the graphics driver I need to exit GUI / Gnome and go to the terminal. How can I do this in Ubuntu 18.04? Ctrl(STRG)+Alt+F1...F7 does not work, neither on the desktop, nor on the login screen... When Ron broke his wand, why didn't he apply for Hogwarts financial aid? We know, from Book Six, that Hogwarts has a financial aid for students in need. It's supposed to cover all expenses regarding materials and school supplies, so it certainly covers wands. So why didn't Ron simply apply for this fund when he broke his wand in Book Two, since his family could not afford a new one?  Seems absurd that no teacher would notice that Ron had a broken wand and inform him there's a school fund. Plot hole?  Obs.: Even if Ron could afford a new wand, one could ask how we would purchase it (you must experiment personally to find a wand that chooses you). It turns out that there's a local branch of Ollivander in Hogsmeade. I'm sure that, under those circumstances, a second-year student like Ron would be allowed to visit Hogsmeade to purchase a new wand. Can a particle be physically observed inside a quantum barrier? I understand that if a particle approaches a finite potential barrier of height $V_0$ with energy $E &lt; V_0$, there is still a finite probability of finding the particle on the other side of the barrier due to quantum tunneling.  My question is, since the wavefunction is nonzero inside the barrier region, is it possible to actually make a position measurement and locate a particle inside the barrier?  I mean, if we can say that "there is a nonzero probability that the particle is inside the barrier", surely this would suggest we can do so?  If not, why not? Am I understanding the whole wavefunction/probability distribution thing right? Adding a script to the page dynamically with jQuery never uses the cached file Purely "algebraic" proof of Young's Inequality states that if $a, b \geq 0$, $p, q &gt; 0$, and $\frac{1}{p} + \frac{1}{q} = 1$, then $$ab\leq \frac{a^p}{p} + \frac{b^q}{q}$$ (with equality only when $a^p = b^q$).  Back when I was in my first course in real analysis, I was assigned this as homework, but I couldn't figure it out.  I kept trying to manipulate the expressions algebraically, and I couldn't get anywhere.  But every proof that I've seen since uses calculus in some way to prove this.  For example, a common proof is based on this  and integration.  The proof on Wikipedia uses the fact that $\log$ is concave, which I believe requires the analytic definition of the logarithm to prove (correct me if I'm wrong).  Can this be proven using just algebraic manipulations?  I know that that is a somewhat vague question, because "algebraic" is not well-defined, but I'm not sure how to make it more rigorous. But for example, the proof when $p = q = 2$ is something I would consider to be "purely algebraic":  $$0 \leq (a - b)^2 = a^2 + b^2 - 2ab,$$ so $$ab \leq \frac{a^2}{2} + \frac{b^2}{2}.$$ 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? Was the singularity at Big Bang perfectly uniform and if so, why did the universe lose its uniformity? Python function attributes - uses and abuses Not many are aware of this feature, but Python's functions (and methods) can have . Behold:  &gt;&gt;&gt; def foo(x): ...     pass ...      &gt;&gt;&gt; foo.score = 10 &gt;&gt;&gt; dir(foo) ['__call__', '__class__', '__delattr__', '__dict__', '__doc__', '__get__', '__getattribute__', '__hash__', '__init__', '__module__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', 'func_closure', 'func_code', 'func_defaults', 'func_dict', 'func_doc', 'func_globals', 'func_name', 'score'] &gt;&gt;&gt; foo.score 10 &gt;&gt;&gt; foo.score += 1 &gt;&gt;&gt; foo.score 11   What are the possible uses and abuses of this feature in Python ? One good use I'm aware of is 's usage of the docstring to associate a syntax rule with a method. But what about custom attributes ? Are there good reasons to use them ? I've got a bunch of files named with a the pattern 99 - DescriptiveName.txt and I'd like to remove the number from the front so I just have DescriptiveName.txt.  How can I do this? Can I do it from the command line or is there a utility that can do this? I've tried to read and understand this:   As a test, since my layout is "Polish, programmer" in the /usr/share/X11/xkb/symbols/pl file I played with remapping the 'q' character to 'x', and it worked just fine.  But what I want, is to remap LWIN (Left Super) to Left Control.   So I tried this: I started editing /usr/share/X11/xkb/symbols/pc file, assuming this is the 'root' of all the other files. Commented out this line:  //key &lt;LWIN&gt; {  [ Super_L       ]   };   and added this one:  key &lt;LWIN&gt; {    [ Control_L     ]   };   and rebooted PC, with no success. I.e. LWIN + C, doesn't copy selected text in text editors to clipboard, instead it just produces the 'c' letter. In the terminal instead of stopping current programm it also just produces the 'c' letter.  Here is my config file:   When I try the xev command and then press the Left Control Key, I see this:  KeyPress event, serial 40, synthetic NO, window 0x5a00001,     root 0x7e, subw 0x0, time 1053321, (374,-259), root:(374,545),     state 0x0, keycode 133 (keysym 0xffe3, Control_L), same_screen YES,     XKeysymToKeycode returns keycode: 37     XLookupString gives 0 bytes:      XmbLookupString gives 0 bytes:      XFilterEvent returns: False  KeyRelease event, serial 40, synthetic NO, window 0x5a00001,     root 0x7e, subw 0x0, time 1053425, (374,-259), root:(374,545),     state 0x0, keycode 133 (keysym 0xffe3, Control_L), same_screen YES,     XKeysymToKeycode returns keycode: 37     XLookupString gives 0 bytes:      XFilterEvent returns: False   BTW. Ask ubuntu suggests me two links to similar questions, but they are old, and suggest using xmodmap, and afaik it's no longer correct answer on Ubuntu >= 16.04 (Xenial) and this is precisely the version I have.  BTW2. I would really like to avoid using apps like Xbindkeys, considering there is a built in solution, which I guess I almost understand, and already spent some time on trying to understand it. Let's assume that one has some HP printer and/or scanner and checked its support status on the corresponding page of HPLIP site - .  So one have the following information: the device Model name, Min. HPLIP Version and Driver Plug-in need.   What should one install to make Ubuntu fully support the HP printer and/or scanner? I have recently installed Ubuntu 14.04 LTS on my laptop Sony Vaio VPCEA16FG. I have been getting system freezes (everything including display, mouse, keyboard stops working and I have to do a restart with the power switch) and there are random popups of "System program problem Detected"  On startup my screen is all splashed with black and white pixels and a System program problem detected message.  My video card info:    01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Madison [Mobility Radeon HD 5650/5750 / 6530M/6550M When I search for Chromium in Ubuntu Software on Ubuntu 16.04, There are 2 options.    Which one should I select?    The same can be observed with , ,  etc. How to insert an item into an array at a specific index (JavaScript)? I am looking for a JavaScript array insert method, in the style of:  arr.insert(index, item)   Preferably in jQuery, but any JavaScript implementation will do at this point. Is a sentence always grammatically incorrect if it has no verb? Is the following grammatically correct? My friend says the second sentence is grammatically incorrect, but couldn't explain why.     I have always been fascinated by statistics. The different ways in   which you could look at data and infer knowledge from it. Physical meaning of quantum operators Let's say we have a wavefunction $\psi$ and a measurement operator $\hat A$.  I understand how eigenvalues and eigenvectors of $\hat A$ describe the possible outcomes of the measurement.  I also understand that the average measurement can be computed as $\langle \psi|\hat A|\psi\rangle$.  It's still not clear to me what the direct meaning of $\hat A |\psi\rangle$ is. It is a wavefunction; how does its corresponding quantum state relate (in physical terms) to the original state $\psi$ and the measurement $\hat A$? When $z\neq 0$, $\arg z$ is defined to be the set $\{\theta \in \mathbb{R} : z=|z|e^{i\theta}\}$.  What if $z=0$? Usually does one leave the argument of $0$ undefined? Or is $\arg 0 = \mathbb{R}$? This is a story that was read on BBC radio about thirty years ago, and this is about as right as I can remember it: The human pilot of a spacecraft is doing some reconnaissance on an alien planet. He crashes but survives. For some reason, no one will know where to look for him. He sees something in the distance that looks like a building of some sort. When he gets there, it seems to be a home. Very much like a human home. There's furniture, but it's strange and uncomfortable . There's food, but it's inedible. There's a faucet but what comes out of it seems more like acid. Everything looks as though it should be right, but it's not. He leaves the house, wanders and after a few days is desperate for water. But there isn't any water anywhere. He's close to death, crawling on the ground and then something happens. There are cracks in the soil and there appears to be water bubbling up from perhaps some underground stream. The water revives him. He goes back to the house and tries the food again. It's delicious and he eats enough to gain back his strength. Then he decides to try the water again. It's pure and wonderful. He takes a shower and the last line of the story is how refreshing the water is on his skin and something about him lifting his tail. According to , the only restriction on self-deleting an answer is that you can't delete an answer that's been accepted.  But I've also heard of users getting in trouble for deleting (non-accepted) answers, and there's the CC-SA license to consider, so -- quite aside from what is technically possible -- my question is when it's permitted to delete your own answer.  Some cases to consider:   You now believe the answer is incorrect. Your answer is correct, but another answer covers the same territory better. You aren't satisfied with the quality/rigor of your answer, e.g. it's speculative and you didn't back it up (on a site that expects that). Something in the answer embarrasses you and you'd rather just make it go away. Your answer wasn't well-received by the community (whether that's "meh" or "make the rep bleeding stop please"). (I'm sure there are others; this isn't meant to be an exhaustive list.)   Does voting matter, either in absolute terms or in comparison to other answers?  For example, maybe it's ok to delete a lower-voted one but not the top-voted answer, or one with score > N??  There is a badge, Disciplined, for deleting your own post of score 3 or higher.  This tells me that it's sometimes ok to delete upvoted answers.  But I'm not sure how much policy we can infer from badges.  Could we have some clarification please? What was Tauriel doing during the events of The Lord of the Rings movies? [Yes, The Hobbit movies are nonsense. But how could I call myself a fantasy fan if I didn't demand my nonsense be as logical as possible?]  Tauriel is presented as a highly-skilled fighter and a combatant for the side of good. Despite this, she apparently did nothing during Sauron's war on the free peoples.  Was she somehow     still mourning Killi, after all these decades?   Was she dead? Or is there another reason she didn't participate?