Virtual public derived basefunction is not visible
Why does an overridden function in the derived class hide other overloads of the base class?
We had in our lecture on numerical analysis the following: Let $\mathrm{Lin}(X,Y)$ be the set of all linear maps $X\rightarrow Y$. Let $A\in\mathrm{Lin}(\mathbb R^l,\mathbb R^n)$ and $B\in\mathrm{Lin}(\mathbb R^n,\mathbb R^m)$ and $\|C\|_{op}:=\max_{\|x\|\leq1}\|C(x)\|$. Then our lecturer followed $\|A\circ B\|_{op}\leq\|A\|_{op}\cdot\|B\|_{op}$. So he didn't prove it and so I've tried it by my own. My attempt: $$\begin{aligned} \|A\circ B\|_{\mathrm{op}} &amp;= \max_{\|x\| &lt; 1}\|(A \circ B)(x)\| \\ &amp; \leq \max_{\|x\| &lt; 1} \|A\|_{\mathrm{op}} \|B(x)\| \\ &amp;= \|A\|_{\mathrm{op}} \max_{\|x\|\leq1}\|B(x)\|\\ &amp;= \|A\|_{\mathrm{op}}\|B\|_{\mathrm{op}} \end{aligned}$$ But this seems too easy. I am really interested in a nice proof so anybody could help? Thanks a lot! Canonical has recently announced , which is Ubuntu with a specific interface for mobile devices.  Where can I get phones with this version of Ubuntu pre-installed? If no devices are available yet, where can I pre-order one? Why do people omit the definite article? I'm used to always hearing or seeing a  before certain nouns.  Yet on certain occasions the article is totally omitted, and it bothers me.  I'm wondering what the justification for omitting the article is, especially when the definite article would seem to be required, or if it is just bad English either on the part of the individual in question or more likely by tradition.  The most frequent place I hear this is at the doctor or dentist's office. In every one I have ever visited, the receptionist or assistant always says things like "Doctor will see you shortly" instead of "The doctor will see you shortly."  The wikipedia article linked above says this: "A definite article indicates that its noun is a particular one (or ones) identifiable to the listener".  In the case of a clinical setting, I know who the doctor is, especially if this is not my first visit.  The people in the office know the doctor even better than I, so it would seem to be inappropriate to omit the article. Even the indefinite article would be incorrect. It further says, under "Zero article":  "In languages having a definite article, the lack of an article specifically indicates that the noun is indefinite."  Since the noun is not indefinite, why are they omitting the article?  Another place I see the article omitted is with the word "bar".  Bartenders apparently don't say "I tend the bar" they say "I tend bar".  Unless a bartender works in multiple bars, it would seem like an article would be required.  Furthermore, "the bar" can mean any bar a person goes to, so even in a case like , it seems like the word "the" should be in the sentence.  The only thing I can think of in this case is maybe the speaker doesn't want to confuse the listener into thinking they work in the legal field.  Is this just a bad habit, a historical corruption or tradition, or is there really a valid reason (or perhaps more than one) for these omissions? What ingredients can I add to no-knead bread to extend its life? Is there anything I can add to a standard no-knead bread recipe to allow the bread to stay softer for longer? Bread baked the night before, while still edible, is not as pliable the next midday.  I currently use bread flour, yeast, salt and water but was thinking of adding milk, butter or eggs. If there is a single food additive I can add I would consider this, but I don't want to adulterate the recipe too much. Duplicate auxiliary verbs in a sentence (may we / should we delete the second?) only display df lines that have more fs usage than 80% root@SERVER ~$ df Filesystem  512-blocks  Free    %Used   Iused   %Iused  Mounted on /dev/YXCV   655360      365632  45% 6322    13% / /dev/ASDF   3801088     670648  83% 41759   32% /usr /dev/ASR    1048576     500496  53% 5555    9%  /var   How can I pipe the df command's output to only display lines that have more usage than 80%?  e.g.: it would only display:  /dev/ASDF   3801088     670648  83% 41759   32% /usr From where do the permanent magnets get energy from? I have a doubt about permanent magnets. If a magnet is permanent it can attract some materials permanently.  Attracting something involves energy. If a permanent magnet can do this forever, from where does this energy come from? How can it not run out of energy? Doesn't it contradict with the laws of energy? If a friend wants to transfer $7000 to me, what is the best way to do it, especially if we don't share the same banks? We could do wire transfer, but that comes with its own fees. Could we also do direct deposit? Paypal doesn't allow such large lump sum transfers.  This would be US-to-US transfer. If I build a package from source how can I uninstall or remove completely? I used source code to build one package such as below:  ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var --libexecdir=/usr/lib --with-package-name="Myplugin" --with-package-origin="http://www.ubuntu.org/" --enable-gtk-doc --disable-static make make install   But unfortunately, i discovered that its the latest version, and has lot of bugs, so i need to remove it/uninstall it. But how can i do so? I tried make clean; make uninstall but still i see it exist:  # pkg-config --list-all | grep Myplugin myplugin-.... $ ls /usr/lib/myplugin/libXYZ.so exist....   How do you remove this now? Resetting Ubuntu to factory settings When does $120$ divide $n^5 - n$ Find n such that $n^5 - n$ is divisible by $120$. (*Here $n$ belongs to the natural number set)  Seems a trivial problem, but the answer mentioned in the text book seemed incomplete to me so I'm here just to ensure whether approach to this problem is correct or not.  So my approach is as follows: We know that $n^5 - n$ can be written as $n^5-n = n(n-1)(n+1)(n^2 + 1)$  Now since it's product of three consecutive natural numbers so it's divisible by $3! = 6$. Now using Fermat's Little theorem we can prove that $n^5= n \mod5$ hence $n^5 - n$ is divisible by $5$ as well. So $n^5 - n$ is divisible by $30$. Now to ensure their is another factor of $4$ in the term we need to ensure that $n^5 - n$ is divisible by $8$. I found that all odd natural numbers and multiples of $8$ makes $n^5 - n$ divisible by $8$, hence $n^5 - n$ is divisible by $120$. But in the text book they have only mentioned odd natural numbers as answer, which seemed incomplete to me.  Thanking everyone in advance:P Are the contents of a loot box determined at the time it is awarded or when it is opened?  For example, if you collect multiple loot boxes before a special event but opened them during the special event, would they have the potential of spawning rewards from that event? How do I combine the NBT tags from two separate commands? I have two commands I'd like to combine into one, but I'm not sure how to go about combining them. Is this possible?   Here are the commands. They work individually, I just can't seem to get them to work together:  /give @p jukebox 1 0 {CanPlaceOn:["minecraft:melon_block"]}     /give @p jukebox 1 0 {display:{Name:"Box"}}   Can you help me to add one of the commands to the other one? Using "of" or apostrophe, which is more common? At what point is the ~/.bashrc file created? how to copy or backup files ignoring dot files I want to back-up all files from my laptop partitions to external HDD.  I ran, for example  cp -a /med*/ravb*/*00   /med*/ravb*/M*L*/7.3GB_CP &amp;&amp; echo "7.3GB BACKED UP PROPERLY" || echo "7.3GB FAILED TO BACK UP"   The issue is that dot files are also getting included which I don't want. What should I do so as to ignore all dot files for backing up. Today, after returning from vacations, I started my QGIS 1.7 and got this terrible message:    Help, anyone? I have a card that is 50% used with 7% interest. The max credit limit on the card is $10,000, and I used $5000. I have another card that is $14,000 and I have $2900 used, but the interest is 14.9%. I want to move the $2900 card to the other card that has a lower interest rate (7%). This will bring the balance close to the max, but the idea is to focus on this one card and bring the balance down as quickly as possible. is this a wise choice? I am looking to purchase a house in 6 months so I thought that this might be enough time to pay it off and keep my score up. My scores are currently in the low 700s. I accidentally removed all the packages starting with the name jpeg with:  sudo apt-get remove jpeg*   This screwed up a lot of things, removed Unity, Firefox, Flash player etc.  I somehow managed to recover the desktop and unity but then a lot of things are still buggy. For example .rpm files and .tag.gz just won't open up at all.  What I want is a way to fix everything that's amiss. Something that is the equivalent of a 'repair installation' with a windows disc.  Any tips, anyone? Switching to different font size(s) locally