Example of a Lie algebra such that the form killing $ K_{\mathfrak g} = 0 $ but $\mathfrak g$ is not nilpotent
When is the Killing form null?
Disabling OBSOLETE error in C# How do I get AMD/Intel Hybrid Graphics drivers to work? On Ubuntu 12.04 my Sony Vaio VPCSE with Intel® HD Graphics 3000 and AMD Radeon™ HD 6630M worked fine with the Catalyst Control Center version 12.6. Also the switching between integrated and discrete graphic card was working.  In both cases, I followed this .  But it is not working on Ubuntu 12.10.   I tested the tutorial with the Catalyst Control Center from the Ubuntu Software Center, the version 12.8 and version 12.9. Always the same problem: After installation process I am able to boot in the login-screen. But after entering the password for my username, only the background-image appears. Unity seems not to be starting. I am only able to reach the context-menu by right clicking the mouse button.  I also tried , but is also does not work for me.  Any ideas what to do to fix this problem?   Update: Same problem on Ubuntu 13.04!  Update: Solution for 13.04 ist not working on Ubuntu 13.10! "It is not possible to check out a single file. The finest level of checkouts you can do is at the directory level."  How do I get around this issue when using Subversion?  We have this folder in Subversion where we keep all our images. I just want to check out one file (image) from that. This folder is really big and has ton of other stuff which I don't need now. Accourding to ,   We often use "been to" when we refer to completed visits to a place:  Have you ever been to Budapest?  Not: Have you ever gone to Budapest?  If the visit is not complete, we use "gone to".  Joan’s just gone to the shop. She’ll be back in about ten minutes. (Joan has not yet returned from the shop.)  Joan’s just been to the shop. She bought some cakes. Would you like one? (Joan has returned from the shop.)  Now, does that rule apply to the  "Have been on a trip" &amp; "Have gone on a trip"?  So, "I have been on a trip" (I completed the trip &amp; currently I am staying at home)  "I have gone on a trip" (I haven't completed the trip &amp; currently I am on the trip)  And what about "gone crazy" &amp; "been crazy".  Does "He has gone crazy" mean now he is still crazy?  Does "He has been crazy" mean now he is not crazy any more?  Are there any differences between "Have been on a trip" vs "Have gone on a trip" and "Have been crazy" vs "Have gone crazy"?  Note: I am not asking about "been to" or "gone to". I am asking about "been on a trip" &amp; "gone on a trip". Do we apply the same rule of "been to" or "gone to" to "been on a trip" &amp; "gone on a trip"?  Note2:  seems to prove that my thinking is right. optexp environment error when compiling with XeLaTeX I have troubles with optexp environment. There is a code  \documentclass[pstricks,margin=12pt]{standalone}  \usepackage{pst-optexp}  \begin{document} \begin{pspicture}(3.2,5) \pnodes(0,3){A}(1,3){BS}(3,3){M1}(1,5){M2}(1,1){PD} \psset{mirrortype=extended, mirrordepth=0.2}  \begin{optexp} \beamsplitter[bsstyle=plate, compname=BS](A)(BS)(PD) \mirror[compname=M1](BS)(M1)(BS) \mirror[compname=M2, variable](BS)(M2)(BS) \lens[compname=L](BS)(PD) \optdetector[compname=Det, dettype=diode](BS)(PD) \addtopsstyle{Beam}{beamwidth=0.2, fillstyle=solid,fillcolor=green!20!white} \drawwidebeam(A){BS}{M1}{BS}{M2}{BS}{L}{Det} \end{optexp} \end{pspicture}  \end{document}   and the result is this    and I get "MiKTeX GPL Ghostscript 9.19: Unrecoverable error, exit code 1" error. When I remove optexp environment, so  \documentclass[pstricks,margin=12pt]{standalone}  \usepackage{pst-optexp}  \begin{document} \begin{pspicture}(3.2,5) \pnodes(0,3){A}(1,3){BS}(3,3){M1}(1,5){M2}(1,1){PD} \psset{mirrortype=extended, mirrordepth=0.2}   \beamsplitter[bsstyle=plate, compname=BS](A)(BS)(PD) \mirror[compname=M1](BS)(M1)(BS) \mirror[compname=M2, variable](BS)(M2)(BS) \lens[compname=L](BS)(PD) \optdetector[compname=Det, dettype=diode](BS)(PD) \addtopsstyle{Beam}{beamwidth=0.2, fillstyle=solid,fillcolor=green!20!white} \drawwidebeam(A){BS}{M1}{BS}{M2}{BS}{L}{Det}  \end{pspicture}  \end{document}   the result is     which is correct but optical components are behind beam. I use XeLatex. What am I doing wrong? Which packages are missing? Thank you (example is from manual "Drawing optical experimental setups" where the code works correctly). In order to protect a portal in the nether I have an obsidian room with an iron door, which works off a switch in the room. The problem is that if I leave the room and someone else on the server closes the door from the inside I can't get back to that portal.  Powering red stone on the outside of the door doesn't seem to work, as the switch inside is already powering it, so I'm guessing something like an XOR gate will be the solution, however I am finding it difficult to see how to make this work in practice. Why so many files in /usr/share/app-install/desktop? For 14.04, I'm trying out Lubuntu LTS.  If I run ls -l /usr/share/app-install/desktop, I get a list of 3085 .desktop files. All except one are dated Apr 18. The exception is:  -rw-r--r-- 1 root root  6328 Mar 28  2013 applications.menu   From the dates, it's clear that all these are installed by default and not by me.   Doesn't each GUI-based program bring in its own .desktop file at the time it's installed (mostly in /usr/share/applications)? Then why are these thousands of other .desktop files needed? From their names, most of them haven't anything to do with Lubuntu. Their names are different from regular .desktop files (such as those in /usr/share/applications): many, not all, are like name:name.desktop whereas the regular ones are just name.desktop. The ones I looked at all have a line with X-AppInstall-Popcon=nnn where nnn is a string of digits. I know that Popcon "gathers statistics determining which packages are the most popular with Ubuntu users". But why is that part of these .desktop files? Force.Com Sidebar - Reference Data From Current Screen On URLs? I am being lead to believe this is possible:  A URL on the Force.Com Sidebar Menu which references data from the currently open page.  i.e., /{!recordId}?nooverride=1    However, this does not work.  The brackets simply turn into percent encoded references on the resultant page.  Is it possible to pass information onto a URL on the Force.Com sidebar? I have a Dell Inspiron 1525 laptop and I am planning on purchasing a mac mini, new version , I am tight on money for a while and want to use my current laptop screen as monitor for mac mini, I just want to know if it is at all possible to do, I have windows 7 and ubuntu 11.04 installed in my laptop, and I don't really care if need to wipe them out, or purchasing a monitos is the only option left, also I am planning to use it for coding and stuff, so VNC is probably not a good choice. Is Ubuntu based on Debian unstable or Debian testing? which of the two it is? How to prove this statement: $\binom{r}{r}+\binom{r+1}{r}+\cdots+\binom{n}{r}=\binom{n+1}{r+1}$ Let $n$ and $r$ be positive integers with $n \ge r$. Prove that   Still a beginner here. Need to learn formatting.  I am guessing by induction? Not sure what or how to go forward with this.  Need help with the proof. Applying options to already loaded package Is there a way to apply some options to a package which is loaded in the cls file I am using? For instance, suppose that the cls file loads graphicx, and I want to apply the option demo to it from my tex file. Implications of parity violation for molecular biology In biology, the concept of parity emerges in the context of chiral molecules, where two molecules exist with the same structure but opposite parity. Interestingly, one enantiomer often strongly predominates over the other in natural biological systems (e.g. D-glucose is ubiquitous, L-glucose is rare in nature).  In physics, it has been established that weak interactions violate parity, which (if I understand correctly) implies a physical difference between left- and right-handed systems.  This suggests to me the following questions: Does parity violation in physics affect the physical or chemical properties of chiral molecules? And does this have any implications for our understanding of biological homochirality? Is it possible for an American to get a Chinese visa in Hong Kong? Roman numerals become “too wide” in table of contents How to share the "Look Back" video from Facebook? On Facebook, there is a  looking back on your Facebook history. Apparently, some people have shared this video with their friends, however I and someone else cannot figure out how to do so. This URL is not unique, it's a global URL which shows the video of who's logged in. People say there's supposed to be a "share" link, but there are no links whatsoever. And, I can't share the URL because it would show them their own videos.  How do I share this video with friends on Facebook?  without using a screen recorder to capture it Today, after returning from vacations, I started my QGIS 1.7 and got this terrible message:    Help, anyone? How to cluster time series? I have a question about cluster analysis. There are 3000 companies, which have to be clustered according to their power usage over 5 years. Each company has values for every hour during 5 years. I would like to find out if some companies have the same pattern in usage power over the time period. The results should be used for daily prediction of power usage. If you have some ideas how to cluster time series in SPSS, please share with me. I don't know how to disconnect a face from the rest of the mesh in edit mode.  This isn't like pressing P to separate the selection into a completely different object. I just want to select a face and disconnect/rip it away from the rest of the mesh but keep it as a part of the original object.  One way to do it would be to duplicate the face with ShiftD and then delete the original face. But I suspect there is a "native" command for disconnecting selected faces and I would like to learn it. I've got a road bike with brake lever shifters, and it's developed a small problem with age: sometimes, the shifter doesn't catch the first time or two I push it. It'll move easily, with no resistance, since it's not actually pulling on the cable, then after a few tries, catch and work normally. The colder the temperature, the more often this happens.  I don't know how the mechanism works internally, so I'm curious what would cause this, and also whether it's (as I suspect) gradual wear of some part of the mechanism, and if it's likely to fail catastrophically, or gradually worsen.