Should I use one SessionScoped bean for all datatables?
How to choose the right bean scope?
What is known about $\mathcal C^\infty$ functions $\mathbb R\to\mathbb R$ that always take rationals to rationals? Are they all quotients of polynomials? If not, are there any that are bounded yet don't tend to a limit for $x\to +\infty$? If there are, then can we also require them to be analytic?  (This is basically just a random musing after I found myself using trigonometric functions twice in unrelated throwaway counterexamples. It struck me that it was kind of conceptual overkill to whip out a transcendental function for the purpose I needed: basically that it had to keep wiggling forever. I couldn't think of a nice non-trancendental function to do this job, however, and now wonder whether that is because they can't exist). Why are there no discrete zero sets of a polynomial in two complex variables? Why is the zero set in $\mathbb{C}\times\mathbb{C}$ of a polynomial $f(x,y)$ in two complex variables always non-discrete (no zero of $f$ is isolated)? Actionbar background is not being changed Live notification shown for own edits When editing an answer, the &quot;new revision&quot; message is shown for a short moment. This makes no sense because the revision you just created is automatically displayed anyway. Is there a reason the British omit the article when they "go to hospital"? Shells have a useful feature where pressing the keyboard UP arrow replaces the contents of the current command line with the previous command that was entered. (And if you do it again, the command before that, and so on.)  I would like a similar feature, where pressing (some other button) replaces the contents of the current command line with the last line of output from the previous command (and if you do it again, the previous line of output , and so on.)  Is there any shell that provides a feature like this?  The motivation is that you often want to run a command, and then run another command with part of the previous commands's output as input. (No, I don't want to do anything involving piping the output of one command into the next. I'm looking for an interactive experience, where you run the first command, see its output, and then get a line of that output into your next command, without having to reach for the mouse to do a clumsy copy-and-paste.) What color can lightsabers be? I just saw the fan film  and the Force-sensitive bounty-hunter, Korbain Thor, wielded an ochre lightsaber (or at least that's what  described it as).   I'm just wondering if ochre is a canon color for a lightsaber? How can I find my hardware details? Is there any built-in software or terminal method allowing me to view the hardware profiles on my system? Windows equivalent of such a feature would be Device Manager. describes how to get the changelog for a given package. However, it's the whole changelog.  What I'd like is a way to see what will be changed in whatever I'm about to upgrade. For example, I was imagining something like:  $ sudo apt-get upgrade --show-changelogs Reading package lists... Done Building dependency tree        Reading state information... Done Calculating upgrade... Done The following packages will be upgraded:   foo     -- adds the bar feature for better snazziness     -- removes the deprecated baz feature  1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 8,864 kB of archives. After this operation, 285 kB disk space will be freed. Do you want to continue [Y/n]?    Unfortunately, I don't see anything like that in the man pages for apt-get. Does this or something similar exist?  UPDATE: I've written a  talking about apt-listchanges and Debian changelogs in a little more depth that incorporates some of the feedback in this question. If a Matrix Has Only Zero as an Eigen-Value Then It Is Nilpotent The following time-frequency correspondence illustration is in .    Also a gif animation version (if the animation doesn't show, please open the following image in a new window):    This picture has so much explanatory power, and I would like to replicate it in TikZ for future use.  Here is what I came up with:  \documentclass{minimal} \usepackage{tikz}  \begin{document} \begin{tikzpicture} [x={(1cm,0.5cm)},z={(0cm,0.5cm)},y={(1cm,-0.2cm)}] \draw[-&gt;,thick,blue!90] (0,6.5,0) -- (6.2,6.5,0) node[right] {Frequency}; \draw[-&gt;,thick,red!90] (0,0,0) -- (0,6.5,0) node[below] {Time}; \draw[-&gt;,thick] (0,0,0) -- (0,0,2) node[above] {Magnitude}; \foreach \x in {0.5,1.5,2.5,3.5,4.5,5.5}{   \draw[blue!50] (\x,0,0)   \foreach \y in {0,0.02,...,6.28}{     -- ({\x},{\y},{sin(\x*\y*(157))/sqrt(2*\x)})   };   \draw[blue!90, thick] (\x,6.5,0) -- (\x,6.5,1/\x); }  \end{tikzpicture} \end{document}   This is the output so far.    I have two questions:   How to produce that red superposed sine wave of all the blue sine waves? I don't know if there is a sum function or I have to use loop yet again? How to make the camera projection in TikZ more similar to the perspective in that wikipedia illustration?   Any suggestion and tweaking of the parameters I used in the sample drawing are welcome as well.  Thanks in advance!    Update 1:  Here is a new version using tikz, more readable than the first one. Yet the superposition of the sine waves are done manually...I still don't know how to use foreach to produce a sum.  \begin{tikzpicture}[x={(1cm,0.5cm)},z={(0cm,0.5cm)},y={(1cm,-0.2cm)}] \draw[-&gt;,thick,black!70] (0,6.5,0) -- (6.2,6.5,0) node[right] {Frequency}; \draw[-&gt;,thick,black!70] (0,0,0) -- (0,6.5,0) node[below right] {Time}; \draw[-&gt;,thick] (0,0,0) -- (0,0,2) node[above] {Magnitude}; \foreach \y in {0.5,1.5,...,5.5}{ \draw [cyan!50, domain=0:2*pi,samples=200,smooth]   plot (\y,\x, {sin(4*\y*\x r)/\y }); \draw[blue, ultra thick] (\y,6.5,0) -- (\y,6.5,1/\y); } \draw [red, thick, domain=0:2*pi,samples=200,smooth]  plot (0,\x, {sin(4*0.5*\x r)/0.5 + sin(4*1.5*\x r)/1.5 + sin(4*2.5*\x r)/2.5 + sin(4*3.5*\x r)/3.5 + sin(4*4.5*\x r)/4.5 + sin(4*5.5*\x r)/5.5} ); \end{tikzpicture}   The result is as follows: Why is $l^\infty$ not separable? Why do harmonics occur when you pluck a string? After MiKTeX update: suddenly all fonts (incl. existing path-referenced ttf files) are not found by fontspec / LuaLaTeX anymore Why does Ubuntu 14.04 LTS use a non-LTS kernel version? Equation number enclosing parentheses misplaced with Polyglossia+Hebrew+amsmath Alternatively, why does the force created by blowing out air feel so much stronger than the force created by sucking in air?  Ok, so forget the human factor involved in blowing out candles. Consider a vacuum cleaner with a suction end and a blower end. Anyone who has tried it out notices the blower end creates a much stronger force than the suction end, despite the discharge being (more or less) equal at both ends.  Why does this happen? Complex number identity by trigonometry Show that $\lvert e^{i\theta} - 1\rvert = 2\lvert\sin(\theta/2)\rvert$ by using the geometry of the triangle with vertices 0, 1, and the midpoint of the line joining 0 and $e^{i\theta}$.  I have been able to show this identity through other means, however I am stuck on how to utilize this particular triangle. How to make Table of Contents manually I'm trying to make table of contents manually, I mean I set the page of each of sections one by one. Here's my target:  and I'm using book class here.  Here's the code that I found   \documentclass[oneside]{book} \renewcommand\contentsname{CONTENTS} \renewcommand\listtablename{LIST OF TABLES} \renewcommand\listfigurename{LIST OF FIGURES} \addtocontents{toc}{{\bfseries Contents\hfill Page No.\bigskip\par}} \addtocontents{lot}{{\bfseries No.\hfill Title\hfill\hfill Page No.\bigskip\par}} \addtocontents{lof}{{\bfseries No.\hfill Title\hfill\hfill Page No.\bigskip\par}}  \usepackage[titles]{tocloft} \usepackage{xcolor,xpatch} \renewcommand\cftbeforechapskip{0ex} \renewcommand\cftchapfont{\mdseries} \renewcommand\cftchappagefont{\mdseries} \renewcommand\cftchappresnum{Chapter~} \renewcommand\cftchapaftersnum{. } \newlength\tocindent \settowidth\tocindent{\cftchapfont\cftchappresnum9\cftchapaftersnum} \edef\cftchapnumwidth{\the\tocindent} \edef\cftsecindent{\the\tocindent} \advance\tocindent2.3em \edef\cftsubsecindent{\the\tocindent} \advance\tocindent3.2em \edef\cftsubsubsecindent{\the\tocindent} \renewcommand\cftsecdotsep{\cftnodots} \renewcommand\cftsubsecdotsep{\cftnodots} \renewcommand\cftsubsubsecdotsep{\cftnodots} \newcommand\tocmainmatter {\renewcommand\cftchappagefont{\color{white}}% } \xapptocmd\mainmatter{\addtocontents{toc}{\protect\tocmainmatter}}{}{}   \newif\ifschaptertoc \makeatletter \renewcommand\@makeschapterhead[1]% {{\parindent \z@ \centering     \normalfont     \interlinepenalty\@M     \Large \bfseries  #1\par\nobreak     \vskip 20\p@ }% \@mkboth{\MakeUppercase{#1}}{\MakeUppercase{#1}}% \ifschaptertoc \addcontentsline{toc}{chapter}{#1}% \fi } \makeatother  \usepackage{blindtext}  \begin{document} \frontmatter  \tableofcontents \schaptertoctrue  \chapter*{ACKNOWLEDGEMENTS} \blindtext  \chapter*{ABSTRACT} \blindtext  \listoftables  \listoffigures  \chapter*{ABBREVIATIONS} \Blindtext  \chapter*{NOTATIONS} \Blindtext  \mainmatter  \chapter{INTRODUCTION} \blindtext  \section{General Background} \blindtext  \section{Objective} \blindtext \subsection{Objective 1} \blindtext \subsection{Objective 2} \blindtext \subsection{Objective 3} \blindtext  \section{Scheme} \blindtext \end{document} Removing clock from the lock-screen I'm using Ubuntu 18.04.  I want to remove the digital clock from the lock screen because I just want to see a good wallpaper there, unobstructed.   How do I go about this?