In contrast to C++, why method visibility can't be narrowed while overriding?
Java, Cannot reduce the visibility of the inherited method from object
I want to setup a new virtual machine with some specified packages (name and version), that are provided.  For example apache2 in version 2.2.20-1ubuntu1 with all dependencies. Even if there is a new version of this package on the servers this one should be installed.  The solution has to work/scale with multiple (n) "setups". Another virtual machine might need an older version of apache2.  I currently know of some possibilities that install the exact packages, but do not scale that good:   Copy all required *.deb to every virtual machine manually and enter: dpkg -i ... -> Could work, but it is very error prone. (Manual scripts etc.) Create and use a new Ubuntu repository for each setup. -> Does not work because I would need n repositories. Setup the machine once and copy the VM / create a snapshot. -> Does not work because I would need to store n VMs.   My problem could be labeled as patch management, but I do not want to update my packages to the current version. My goal is to install old packages. I want to do this using the Math.Round function If $A\subset\mathbb{R^2}$ is countable, is $\mathbb{R^2}\setminus A$ path connected? Possible Duplicate:          As the topic,if $A\subset\mathbb{R^2}$ is countable, does $\mathbb{R^2}\setminus A$ path connected??? I know the answer is it is path connected but not sure how to prove it. Duplicate explanation should encourage improvement of original The new closed-as-duplicate banner says:     This question has been asked before and already has an answer. If those answers do not fully address your question, please .   I think it should instead say     This question has been asked before and already has an answer. If answers there do not fully address your question, please  or  to the pre-existing one.   &mdash; to discourage re-re-asking the same question. (I also changed "those answers", which has no plural , to "answers there", which doesn't need one.)    As of September 19, 2013, the original text quoted above has returned here. Expected number of siblings, given the expectation of children in a family The number of children in a family is a random variable $X$, where    $ \mathbb E(X) = 1.8 $ and $Var(X) = 0.36 $. If we randomly choose a child, which is the expected number of its siblings?      (it is given that the answer $&gt; 0.8$)   Let the number of a child's siblings be a random variable $Y$, so we are looking for $ \mathbb E(Y) $.  If found that,  $$ \mathbb E(Y) = \sum_{k=0}^{\infty}k \; \mathbb P(Y=k) = \sum_{k=0}^{\infty}k \; \mathbb P(X=k+1) = $$ $$ = \sum_{k=0}^{\infty}k \; \mathbb P(X=k)-\sum_{k=0}^{\infty}\mathbb P(X=k) +\mathbb P(X=0)= \mathbb E(X)-1+\mathbb P(X=0) $$ which is indeed greater than $0.8$, if  $\; \mathbb P(X=0)&gt;0$.  But, I don't know how to make use of the variance to find the final answer.  Thank you in advance Simulate bad cell phone reception in the lab Partition of a set and Hall's theorem Make a computer act as a virtual USB device for other equipments Proving an identity for Bernoulli polynomials Consider the Bernoulli polynomials $B_n(x)$ given by the expansion  $$\frac{te^{xt}}{e^t-1} = \sum\limits_{n=0}^{\infty}B_n(x)\frac{t^n}{n!}.$$  I want to prove the identity $$B_n(1-x)=(-1)^nB_n(x).$$  This formula is given in a lot of books, but unfortunately without any proof. Therefore I'm wondering how to prove it. Do you have any idea?  I tried for instance:  $\sum\limits_{n=0}^{\infty}B_n(1-x)\frac{t^n}{n!}=\frac{te^{-xt}}{e^t-1}e^t=\left(\sum\limits_{n=0}^{\infty}B_n(-x)\frac{t^n}{n!}\right)\sum\limits_{n=0}^{\infty}\frac{t^n}{n!}=\sum\limits_{n=0}^{\infty}\left(\sum\limits_{l=0}^n\binom{n}{l}B_{l}(-x)  \right)\frac{t^n}{n!}$.  Hence  $B_n(1-x)=\sum\limits_{l=0}^n\binom{n}{l}B_{l}(-x)$.  But I do not know how to proceed.  On the other hand I know that $B_n(x+1)-B_n(x)=n x^{n-1}$. Hence  $B_{n}(1-x)=B_{n}(-x)-n(-x)^{n-1}$. But again, I do not know how I can go further.   Hopefully someone can help me.  Best regards Whenever both my roommate and I use the wifi in a certain room in our apartment, it slows dramatically for me. It doesn't slow for him. If he uses it in another room, it's fine; if I use it in another room together with him, it's fine; it's just in this particular room. Does anyone know of a reason this could be? Attributing contributions to academic work that occur in Stack Exchange I want to install the  on my iPhone. On the phone I have iOS 7. When I try to install the App, it tells me it needs at least version 8 of iOS.  I do not want to upgrade my iOS version, especially for the sole purpose of installing an App. However, I do want to use it, it's kind of important.  I searched for a while about how to do this, but I could only find solutions that would work if you installed the App before and it shows up on the "Purchases" page in iTunes or something like that. And this doesn't apply to this case.    How can I install an older version of the App (one that requires "only" iOS 7) without having to upgrade the operating system on my iPhone ? Adding layers to GeoPackage using PyQGIS What exactly is a hat?  I have seen a lot of people arguing the significance of hats and the limited edition hats. I know the hats are sort of linked to the Winterbash stuff, but what exactly is a hat, what does it do, how do I get one?  Is there a full list of hats? Number of equivalence relations on a set Is "Five dollars is all I have" correct? I want to emphasize that I only have 5 dollars, so can I use the sentence:     Five dollars is all I have.   Or must it be:      Five dollars are all I have.   Please give the explanation as well. How to differentiate formally? How often is the password asked for sudo commands? Where can I set it up? Submitting a form by pressing enter without a submit button Does a creature with Lifelink provide lifegain equal to its power, or the defender's toughness?