When we define complex numbers we start creating a field on R2. I think that is impossible to do the same thing on R3 and, in general, on Rn. Do a theorem exist which prove that?
Since there are  complex numbers (2 dimensions) and quaternions (4 dimensions), it follows intuitively that there ought to be something in between for 3 dimensions ("triernions").   Yet no one uses these. Why is this?
SF TV show about a war between humans and aliens? How can I determine the current brew package count? I tried to get the number of available brew packages by running  brew search | wc -l   but I don't know how accurate this really is. What do I need to take into account to get a more correct number?  PS: macports lists 19,889 packages online Residence has changed - Must I re-apply for ESTA? I have an old, but still valid ESTA, with the country of residence showing my home country. However, I have recently moved for education in the UK. Do I have to apply for a new one?  Nothing else has changed - country of citizenship, passport, names etc Can I view the Markdown-source of an unedited question/answer? Once a post has been edited, you can go into the revision list, and click "View Source".  If a post has not been edited (and I don't have the edit privilege) is there any way to see the raw Markdown?  The reason I ask I because of  - it's impossible to see the source markdown, and how it's different from the rendered Markdown.  Not exactly a huge issue, just curious! Convert a preprocessor token to a string I'm looking for a way to convert a preprocessor token to a string.  Specifically, I've somewhere got:  #define MAX_LEN 16   and I want to use it to prevent buffer overrun:  char val[MAX_LEN+1]; // room for \0 sscanf(buf, "%"MAX_LEN"s", val);   I'm open to other ways to accomplish the same thing, but standard library only. What is the best way to filter a Java Collection? I want to filter a java.util.Collection based on a predicate. Is it possible to make abstract classes in Python? How do "badges" work? Installing Wine on 64 Bit I have tried to install wine through the software center and terminal and I get this error.  chris@ubuntu:~$ sudo apt-get install wine1.5 [sudo] password for chris:  Reading package lists... Done Building dependency tree        Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation:  The following packages have unmet dependencies:  wine1.5 : Depends: wine1.5-i386 (= 1.5.16-0ubuntu1) but it is not installable            Recommends: gnome-exe-thumbnailer but it is not going to be installed or                        kde-runtime but it is not going to be installed            Recommends: ttf-droid            Recommends: ttf-mscorefonts-installer but it is not going to be installed            Recommends: ttf-umefont but it is not going to be installed            Recommends: ttf-unfonts-core but it is not going to be installed            Recommends: winbind but it is not going to be installed            Recommends: winetricks but it is not going to be installed E: Unable to correct problems, you have held broken packages. In the experiments for photoelectric emission, the light is incident on one face of the emitting plate, for example the anode, when determining the stopping potential. The electrons are emitted by this face of the plate. Why are the electrons emitted in the direction of the incident light, and not opposite to it?  I have read a little about photons (the key words being, a little), and from what i gather, they have an intrinsic momentum $p=h/\lambda$, which is transferred entirely to the particle that absorbs it (along with the energy $h\nu$). This should imply that the electrons try to move further into the cathode, and not escape it! What is the fault in the reasoning?  Thanks! iOS app 1.4.3, iOS 9.2.1  While viewing a post, the app somehow ended up in a state where it refuses to do much of anything.  What does work:   Swipe-scrolling vertically Jumping to the previous / next post using the up / down buttons    Everything else, though, has no effect:   Swipe-scrolling horizontally will not return to the previous view Tapping on a code block will not zoom to code-block view Tapping Delete button to delete a post will show a confirmation dialog, but saying yes will not cause deletion The Add Comment button brings up the text field, but I cannot type anything in it; I can only dismiss it None of the other buttons (Share, More, etc.) do anything Cannot view user profiles or revision history Tapping on links in a post or comment will not show a web page Tapping on a tag shows some visual feedback with a temporary color change, but doesn't do anything else   I still receive push notifications, but tapping on them doesn't take me anywhere. What is the principle of underdetermination? While studying I read about the principle of underdetermination of scientific theories. I made some researches online but I am more confused than before. I read about the Quine-Duhem holistic thesis, but I do not know if is the same as underdetermination. Currently, if you access a deleted question you will get a short message informing you that the question has been deleted. However, if you click on a direct link to a deleted answer or comment (which you can get via notifications), nothing is displayed.  This is naturally quite confusing as you will get the message about a new answer or comment via notifications, click on the link and simply see nothing.  Therefore, I propose to display some sort of message to the user, informing her/him that the answer or question has been deleted. Note that this is different from always showing a deleted answer/comment, as I specifically request it in case you access the specific URL.  One example for a comment would be:   One example for a deleted answer is:   This question is related to ,  but requests a feature to circumvent the problem altogether. Are GUID collisions possible? I'm working on a database in SQL Server 2000 that uses a GUID for each user that uses the app it's tied to. Somehow, two users ended up with the same GUID. I know that microsoft uses an algorithm to generate a random GUID that has an extremely low chance of causing collisons, but is a collision still possible? Output from ls has newlines but displays on a single line. Why? I think I may be overlooking a relatively fundamental point regarding shell. Output from the ls command by default separates output with newlines, but the shell displays the output on a single line.  Can anyone explain this to me? I had always presumed that the output was simply separated by spaces, but now that I see the output separated by newlines, I would expect the output to be displaying on separate lines.  Example:  cpoweradm@debian:~/lpi103-4$ ls text* text1  text2  text3   od shows that the output is separated by newlines:  cpoweradm@debian:~/lpi103-4$ ls text* | od -c 0000000   t   e   x   t   1  \n   t   e   x   t   2  \n   t   e   x   t 0000020   3  \n 0000022   If newlines are present, then why doesn't the output display as:  text1  text2 text3 I am looking at collecting spatial information from a range of stakeholders to identify opportunities within a landscape.  However, the data that we are collecting are not presently mapped and so we wish to use an interactive method to get this information onto a map.  Which online websites/methods would people recommend for circulating to a non-technical audience to try and get them to map what they know?    Where the emphasis is on ease of use by the stakeholder. Remember all opened files with split windows and their positions in Emacs Reserved words as names or identifiers Is there any tricky way to use Java reserved words as variable, method, class, interface, package, or enum constant names? Is a small size block cipher usable? Consider a block cipher with a key of size 128 bits but a small block size, say 32 bits.  Is this kind of block cipher secure?  I would like to know to what extent I can use a small block cipher, like a 32 bit block cipher. What are the constraints so that the use is acceptable in a real life application.  For instance, if we use a one-time key, that is, to encrypt only one message. Besides, the message could be small.  Suppose that when we want so send one file, we perform a key agreement so that we use the key for one message. This scenario is not efficient, but the CPA find-then-guess game is not adequate in this case. Ability to view your own questions The app doesn't have a way to show your own questions. It would be nice to get a quick handle to those.