When I delete a comment, then try to delete another comment too quickly, the error message talks about comment votes
Deleting a comment (mine) shouldn't count as a comment vote
Why do different humans look different? Although farmers appear to be able to tell their cows apart, cows look very much alike to me. And this similarity in appearance seems to be a general trait across the animal kingdom: one individual of one animal species looks much like another.  Why do human facial and body shapes vary so much?  I understand that human beings live in many different environments (e.g. hot and cold) and have adapted to these (e.g. through lighter or darker skin color), but there seems to be much variation that has no apparent evolutionary purpose. So does the difference have a purpose in itself? That is, did we evlove to vary in appearance, and what is the purpose of this variation? I just uninstalled TeX Live 2016 and installed TeX Live 2017 and I noticed that the vertical alignment of author and title in any beamer presentation with Warsaw theme has been disrupted. In this example the author is JESTIN and the title is Beamer Intro. How can I vertical center them?  Moreover, I just found the same bug in the beamer guide obtained writing texdoc beamer in the command prompt, in the part of a warsaw presentation.    Here is my code:  \documentclass{beamer}  \usetheme{warsaw}  \title[Beamer Intro]{Beamer - Introduction to \LaTeX{} presentation making} \author[JESTIN]{Jestin Joy}  \begin{document}  \begin{frame}   \titlepage \end{frame}  \end{document} Doing heatmap from line data in QGIS? What happened to Saruman after he was knifed by Grima? How to install Metasploit and Armitage I want to install metasploit and armitage on my ubuntu 16.04 LTS laptop running kernel 4.6  I've read blogs and posts on how to install it but the problem is is that they are outdated. The packages are not there anymore and or the commands dont work.  If anyone can give me an updated tutorial on how to install it that would be great. I also think other users that see this post and want to install it will also be thankful. Thanks. Choosing the best model from among different "best" models How do you choose a model from among different models chosen by different methods (e.g. backwards or forwards selection)?  Also what is a parsimonious model? I'm practicing proofs and given the following statement:  Let $\Sigma$ be an alphabet, $\epsilon$ the empty word and $\sigma:\Sigma^{*}\rightarrow\Sigma^{*}$ an operation which for $a\in\Sigma$ and $w\in\Sigma^{*}$ is defined as $$\sigma(\epsilon)=\epsilon,\\\sigma(wa)=a\sigma(w).$$  I would like to prove through induction that $\sigma$ is equal to the word reversal operation $rev$ meaning that $\sigma(w)=rev(w)=w_{n}...w_{1}$ for every $w=w_{1}...w_{n}\in\Sigma^{*}$.  My suggestion is as follows:  For $w=\epsilon$ we have $$\sigma(w)=\sigma(\epsilon)=\epsilon=rev(\epsilon)=rev(w).$$  Let $w=xa$ with $x\in\Sigma^{*}$ and $a\in\Sigma$, then $$\sigma(x)=x_{n}...x_{1}=rev(x).$$  Thus we also have $$\sigma(w)=\sigma(xa)=\sigma(x_{1}...x_{n}a)=a\sigma(x_{1}...x_{n})=ax_{n}\sigma(x_{1}...x_{n-1})=...=ax_n...x_{1}=rev(x_{1}...x_{n}a)=rev(xa)=rev(w).$$  Does that constitute a correct and sufficient proof? If not, I would very much appreciate your feedback. How do I ensure that a Python while-loop takes a particular amount of time to run? If $a_n$ goes to zero, can we find signs $s_n$ such that $\sum s_n a_n$ converges? Let $a_n$ be a sequence of complex numbers that converge to zero. Can we always find $s_n \in \{-1,1\}$ such that $\sum_{n=1}^{\infty} s_n a_n$ converges?  If the $a_n$ are real numbers, we can find such a sequence $s_n$. If the partial sum of the first $N$ terms is positive we make sure the following terms are negative until the sum becomes less than zero. Then we switch to making the terms positive until the partial sum becomes greater than zero, and so on. It is easy to see that the partial sums will either tend monotonically towards zero, or oscillate around zero with decreasing amplitude.   Edit: Actually there is no reason that the partials sums should go to zero in the monotone case. They will still converge however. Is there any difference between "offense" and "offence"? Is the graviton hypothetical? Wikipedia lists the  as a hypothetical particle. I wonder whether graviton is indeed hypothetical or does its existence directly follow from modern physics? Does observation of gravitational waves amount to the discovery of graviton or could there be gravitational waves not composed of gravitons? If we have a complex scalar $\phi$ we know that the gauge-invariant interaction with $A$ is given by $A^\mu J_\mu$, where $J$ is the Noether current of the $U(1)$ symmetry of the Lagrangian $$ J_\mu\sim \phi^\dagger\partial_\mu\phi-\phi\partial_\mu \phi^\dagger \tag{1} $$  If we have a real scalar instead, $J=0$ and the field doesn't couple to $A$: real particles aren't charged.  My question is: what if we took $$ J_\mu\sim \phi\partial_\mu\phi \tag{2} $$ to couple $\phi$ to $A$? The interaction is Lorentz invariant and renormalisable, but it is not gauge-invariant, which is probably a bad thing. At what point would this theory break down?  This is probably very naïve, but I think that the Feynman rules for this theory are straightforward. So I guess the theory makes sense at least perturbatively. The theory is probably flawed at a more fundamental level, but I cant't seem to find where (some kind of gauge anomaly perhaps?) Does inverting the "if" improve performance? I was writing a program in C++ to find all solutions of ab = c, where a, b and c together use all the digits 0-9 exactly once. The program looped over values of a and b, and it ran a digit-counting routine each time on a, b and ab to check if the digits condition was satisfied.  However, spurious solutions can be generated when ab overflows the integer limit. I ended up checking for this using code like:  unsigned long b, c, c_test; ... c_test=c*b;         // Possible overflow if (c_test/b != c) {/* There has been an overflow*/} else c=c_test;      // No overflow   Is there a better way of testing for overflow? I know that some chips have an internal flag that is set when overflow occurs, but I've never seen it accessed through C or C++.    Beware that signed int overflow is undefined behaviour in C and C++, and thus you have to detect it without actually causing it. For signed int overflow before addition, see . Prove $\mathbb{Z}_2 \times \mathbb{Z}_2$ is not isomorphic to $\mathbb{Z}_4$ In trying to understand why there are two sets of groups of order 4.  I know that there exists the Vierergruppe of $\mathbb{Z}_2 \times \mathbb{Z}_2$ and the group $\mathbb{Z}_4$ but I do not understand why they are not isomorphic On sites with new responsive theme, word wrap on long titles breaks in the middle of a word Why is a boolean value in JTable showing as true/false instead of a checkbox? Fourier transform of the indicator of the unit ball Let $x_n$ be a sequence of the type described above. It is not monotonic in general, so boundedness won't help. So, it seems as if I should show it's Cauchy. A wrong way to do this would be as follows (I'm on a mobile device, so I can't type absolute values. Bear with me.) $$\left|x_{n+1} - x_n\right| \leq \frac{1}{n^2}.$$ So, we have $$ \left|x_m -x_n\right| \leq \sum_{k=n}^{m} \frac{1}{k^2}$$ which is itself Cauchy, etc., etc. But, of course, I can't just use absolute values like that. One thing I have shown is that $x_n$ is bounded. Inductively, one may show $$ \limsup_{n \to \infty} x_n \leq x_k + \sum_{k=n}^{\infty} \frac{1}{k^2},$$ although I'm not sure this helps or matters at all. Thanks in advance.  Disclaimer I've noticed that asking a large number of questions in quick succession on this site is often frowned upon, especially when little or no effort has been given by the asker. However, I am preparing for a large test in a few days and will be sifting through dozens of problems. Therefore, I may post a couple a day. I will only do so when I have made some initial, meaningful progress. Thanks. What is the difference between an "API," a "framework," an "IDE," and an "engine?"