This may seem like a stupid question.  I'm using Ubuntu 15.10 with GNOME Terminal 3.16.2. When I was new to the system, I often typed 'l' or 'la' instead of 'ls' to list files, and would then be told that these were not valid commands. I obviously then typed 'ls' properly. Now I notice that typing 'l' and 'la' do the same thing as 'ls'.  What's going on here? Has the terminal learnt the common mistakes that I make, and made aliases to account for them, or is this a new feature that I've installed without realising?
There is a command l available on my machine which appears to do nothing.  which l also produces no output. Is this a real command, and does it actually do anything?
Upon system restart, dconf editor doesn't save changes I can use the dconf-editor to change my touchpad settings to natural scrolling, but upon system restart the settings get reverted. (But not on sleep or hibernate.) When I open the editor, the option is still orange indicating it has been changed. when I uncheck and recheck the natural scroll option, it is re-enabled. Is there a fix, or am I changing the wrong option? The path is org > gnome > settings-daemon > peripherals > touchpad > natural-scroll.  Currently running 13.10 Random integer in VB.NET I need to generate a random integer between 1 and n (where n is a positive whole number) to use for a unit test. I don't need something overly complicated to ensure true randomness - just an old-fashioned random number.  How would I do that? Smooth rendering of bitmap fonts The stress tensor can be written as: $$\sigma_{ij}=-p \delta_{ij}+\sigma'_{ij}\label{1}\tag{1}$$ where $\sigma_{ij}'$ is called the extra stress tensor.   From what I understand pressure is pressure is force per unit area, so that the force acting on the surface $d\vec A$ is given by:  $$\vec F=-p d\vec A\label{2}\tag{2}$$ (This has the effect that the force on an infinitesimally thin surface due to a continuous pressure is zero). However, $\sigma_{ij}$ represent the force in the $i$ direction on a surface with normal in the $\hat e_j$ direction. So the force acting on a surface $d \vec A$ must be: $$F_i=\sigma_{ij}dA_j\label{3}\tag{3}$$ Equations (2) and (3) clearly do not agree (even if we look soley at the force in the $d\vec A$ direction they don't agree). So my question is what is the exact meaning of pressure in expression (1) and why do we not have: $$\sigma_{ii}=-p$$ Is there any way to backtrack to previous areas? The special linear group $\text{SL}_n(\mathbb{R})$ is its own commutator Let $SL_n(\mathbb{R})$ be the set of $n\times n$ matrix with determinant one. Where can I find a proof that $[SL_n(\mathbb{R}),SL_n(\mathbb{R})]=SL_n(\mathbb{R})$? I've seen this result mentioned in several places, but couldn't find a proof.  For reference, the commutator $[SL_n(\mathbb{R}),SL_n(\mathbb{R})]$ is defined as the group generated by the set of all elements of the form $a^{-1}b^{-1}ab$, with $a,b\in SL_n(\mathbb{R})$. how to prove the chain rule? I have just learnt about the chain rule but my book doesn't mention a proof on it. I tried to write a proof myself but can't write it. So can someone please tell me about the proof for the chain rule in elementary terms because I have just started learning calculus. Change web folders names with uppercase to lowercase or not? Why is charge of the electron negative? check if numbers from command line are powers of 2 A better class to update property files? Though java.util.properties allows reading and writing properties file, the writing does not preserve the formatting. Not surprising, because it is not tied to the property file.  Is there a PropertyFile class out there -- or some such -- that preserves comments and blank lines and updates property values in place? Why is sample standard deviation a biased estimator of $\sigma$? describes the first-order vs. second-order logic as follows:     First-order logic uses only variables that range over individuals (elements of the domain of discourse); second-order logic has these variables as well as additional variables that range over sets of individuals.   It gives $\forall P\,\forall x (x \in P \lor x \notin P)$ as an SO-logic formula, which makes perfect sense to me.  However, in a , the poster claimed that $\forall x\forall y(x=y\leftrightarrow\forall z(z\in x\leftrightarrow z\in y))$ is an FO formula. I think this must not be the case, since in the above formula, $x$ and $y$ are sets of individuals, while $z$ is an individual (and therefore this must be an SO formula).  I mentioned this as a comment, but two users commented that ZF can be entirely described by FO logic, and therefore $\forall x\forall y(x=y\leftrightarrow\forall z(z\in x\leftrightarrow z\in y))$ is an FO formula.  I'm confused. Could someone explain this please? Exponent and abelian groups What exponent $e$ can guarantee the group to be abelian? Are there any known results except the case $e = 2$? Thanks for help. What's the function of the "|" (pipe) operator? Footnote, non-inline syntax? I would like to use footnotes without cluttering the container paragraph. Something like:  This is a very long complex\footnote[a] sentence.  \foottext[a]{So complex that I would prefer to pull out the footnote text.}   The idea comes from the [linktext][1], [1]: http://url.com markdown syntax. No sound (speakers/jack) + microphone's dead after spilling water When is a gerund supposed to be preceded by a possessive adjective/determiner? Java: Date from unix timestamp What is wrong with \ifnum#1=0.09\relax? The following code does not compile with the following error message     Missing = inserted for \ifnum   \documentclass[pstricks,border=4pt]{standalone} \usepackage{multido}  \psset{linewidth=.5\pslinewidth} \psset{xunit=2cm}  \newcommand\FixedScale[1]{%     \multips(0,0)(.1,0){\the\numexpr10*#1+1\relax}{\psline(0,0)(0,-3pt)}     \multips(0,0)(.5,0){\the\numexpr2*#1+1\relax}{\psline(0,0)(0,-6pt)}     \multips(0,0)(1,0){\the\numexpr#1+1\relax}{\psline(0,0)(0,-9pt)}     \multido{\i=0+1}{\the\numexpr#1+1\relax}{\uput[-90](\i,-5pt){$\i$}} }  \newcommand\VernierScale[2][0.09]{%     \rput(#2,0){%     \psset{xunit=#1,linecolor=red}%     \multips(0,0)(1,0){11}{\psline(0,0)(0,3pt)}%     \multips(5,0)(5,0){1}{\psline(0,0)(0,6pt)}%     \multips(0,0)(10,0){2}{\psline(0,0)(0,9pt)}%     \ifnum#1=0.11\relax         \multido{\i=0+5}{3}{\uput[90](\i,8pt){\tiny$\the\numexpr10-\i\relax$}}     \else         \multido{\i=0+5}{3}{\uput[90](\i,8pt){\tiny$\i$}}     \fi     } }  \begin{document} \multido{\n=0.00+0.01}{21}{% \begin{pspicture}(0,-.5)(2,.55) \FixedScale{2} \VernierScale[0.09]{\n} \end{pspicture}} \end{document}   What is wrong with \ifnum#1=0.09\relax?