Where can I find source code for the Java data structures?
Where can I see the source code of the Sun JDK?
Using both “one’s” and “their” to refer to the same entity How can I prove that the additive group of rationals is not isomorphic to a direct product of two nontrivial groups? I am working through Paolo Aluffi's new GSM text on my own (self-study). On page 63, he asks the reader to     Prove that $\Bbb{Q}$ is not the direct product of two nontrivial groups.   For some context, this is an exercise following a section entitled "The category Grp".  I am assuming that he means "is not isomorphic to the direct product of two nontrivial groups", and I can see two possible ways to proceed with this proof, but have been unsuccessful with either approach.    Approach 1:  Show that the additive group of rationals has a property that is preserved by isomorphism that the direct product of two nontrivial groups does not have or vice-versa.  This seems challenging unless I can significantly narrow down the properties that a direct product of two nontrivial groups that was isomorphic to $\Bbb{Q}$ would necessarily have.  Approach 2:  Considering the section in which this question occurs, show that if $G$ and $H$ are nontrivial groups and $\Bbb{Q} \cong G \times H$, then there are homomorphisms $\varphi_{G}:\Bbb{Q} \rightarrow G$ and $\varphi_{H}:\Bbb{Q} \rightarrow H$ which do not factor or do not factor uniquely through the product $G \times H$.  This would be a contradiction, as $G \times H$ is a final object in the category Grp.  I would greatly appreciate suggestions on how to proceed further with either of these approaches or with alternate approaches. Does a word rhyme with itself? Why does the guestbook chatbox not produce any network activity? I was trying to test if I was able to automatically send a message through curl by inspecting the network activity on chrome and getting the curl command, but I found out that in spite of messages showing up in the gestbook chat there was no any network activity. Why? Mouseover tooltip for delete count is wrong It is true that $P(X&gt;t+s|X&gt;t)=P(X&gt;s)$ for certain values $t$ and $s$.  However, how can I show that this still holds if:   $T$ is a continuous random variable. That is $P(X&gt;T+s|X&gt;T)=P(X&gt;s)$ Both $T$ and $S$ are continuous RVs: $P(X&gt;T+S|X&gt;T)=P(X&gt;S)$   All the random variables are independent. Show that $\sum\limits_{n=0}^\infty \frac{z}{(1+z^2)^n}$ converges for all $z\in \mathbb{C}$ outside $|1+z^2|=1$ Show that $\sum\limits_{n=0}^\infty \frac{z}{(1+z^2)^n}$ converges for all $z\in \mathbb{C}$ outside $|1+z^2|=1$  Actually, I have the problem to understand the meaning of "outside $|1+z^2|=1$". If it means that the collection of $z\in\mathbb{C}$ such that $|1+z^2|&gt;1.$ This problem will be easy to verify since for each given $z$ with $|1+z^2|&gt;1$, then we have $|1+z^2|^{-1}&lt;1$. Then, it is the geometric series with common ratio less than $1$ which implies that the series converges.   Do I have correct interpretation with "outside $|1+z^2|=1$"? If not, what is the correct interpretation with this? Thanks. How can I increment a date by one day in Java? I'm working with a date in this format: yyyy-mm-dd.  How can I increment this date by one day? Periodic function implies periodic primitive? If $f$ is a periodic function with $T = \pi$, does that mean that $F$ (a primitive of $f$) has the same period ? What about the inverse implication (periodic primitive implies periodic function) ? Same update keeps showing up everyday Create a virtual file that is actually a command Is there any way to create a virtual file, such that reading from the file actually reads from the stdout of a command; writing to the file is acually writing to the stdin of a command?  So far I have kludged this with an inotifywait on a file, which calls a command when the file is modified, taking it's input from the file and writing back to it.  I don't like that the inotifywait has to be constantly restarted though (and I have to ensure that it is always running). I only use this file perhaps twice a week. Compute the sum of the series $\sum_{n=1}^{\infty} \frac{1}{n \cdot 2^n}$ What would be the sum of the following series?  $$\sum_{n=1}^{\infty} \frac{1}{n \cdot 2^n}$$  Thanks This is somewhat of a beginner's question, but how does one interpret an exp(B) result of 6.012 in a multinomial logistic regression model?  1) is it 6.012-1.0 = 5.012 = 5012% increase in risk?  or  2) 6.012/(1+6.012) = 0.857 = 85.7% increase in risk?  In case both alternatives are incorrect, can someone please mention the correct way?  Ive searched many resources on the internet and I get to these two alternatives, and I am not entirely sure which one is correct. Why does a mirror split my laser beam? What will be a smoother transition into GNOME for Ubuntu 18.04-- Ubuntu GNOME or Vanilla Ubuntu? ^^^^ Will Ubuntu GNOME upgrade to Ubuntu 18.04, or will support discontinue when 18.04 is released?? Just want to know what's better to run right now so I can upgrade and not have to reinstall later(I intend to see this transition through)-- GNOME installed correctly on vanilla Ubuntu, or Ubuntu GNOME? Is it adviseable to stack internal hard disk over each other (after removing them from the casing) Would it damage or cause any interference to the non-operational (whereby electricity or power is removed or disconnected from the hard disk and it will be store inside a cupboard or container either made of plastic or metal) hard disks (IDE, SATA)? How do I left-align entries in a matrix with \begin{matrix}? I'd like to left align the -1 entry in the following matrix so that the 1s line up. Is there a way to get matrices to ignore signs in that way?  \begin{matrix}     1 &amp; 1  \\     1 &amp; -1 \\ \end{matrix}   Using \flushright{-1} doesn't seem to work. Character Limit in HTML How do you impose a character limit on a text input in HTML? How does Stack Overflow save and show tags? I am a user on Stack&nbsp;Overflow, and I think every page that shows questions, display all tags and the questions. Are the tags saved in a tags table or are they included together with the questions table? Finding centrelines from polygons in QGIS? I was wondering if there is a way to create centre lines from polygons in QGIS? I have a polygon layer, but ideally need the centrelines as a separate file.