What's the difference between substitution and permutation in DES? From my understanding substitution is replacing the data with new data and permutation is just rearranging the data?
I've noticed confusing definitions about permutation and substitution, preventing me from understanding the difference.  A permutation changes the order of distinct elements of a set, but this can be written as a function changing one element by another, exactly as a substitution.  So, how exactly can we distinguish between these two notions?  This question is interesting since we have these two notions in block ciphers, in which S-boxes perform substitution. The problem is that this table is used to replace one element by another, exactly like a permutation.
A zero-dimensional ring is Noetherian? Proposition: Let $A$ be a non-zero ring that is not a field. Suppose $A$ is zero dimensional. Then it is Noetherian.   Proof: Let $p$ be a prime ideal of $A$. If $p$ is not maximal, then $p \subsetneq m$ for a maximal ideal $m$. Hence $dim A \ge 1$, contradiction. Hence every prime ideal is maximal. Consequently, every increasing (or decreasing) chain of prime ideals will be trivial in the sense that it will have length $0$. Hence the ring is Noetherian (and Artinian).  Is there a problem with the above proof? While using the Pixel Inspector, whenever I click "copy all values" it only copies values that you can see on the screen. Anyone know a solution? I need all the values to count the number of times 1, 2, and 0 appear on the graph. How to hide quoted text in Lion Mail? In Mail's conversation view, by default, quoted text is hidden and can be shown by clicking "See More from XXX" in the bottom of each message. After clicking that, how can quoted text be hidden again? I want to do a survey of textbooks in set theory. Amazon returns 3582 books for the keywords "set theory". A small somewhat random selection with number of references in Google scholar is the following.   Two questions:    What textbooks in set-theory are considered standard?  What is a good place to aggregate standard references (of textbooks)?    (I'm only interested in text-books, which as a format already provide a kind of standardization)  Textbooks on set theory (author: title (year) #Google Scholar citations )   Thomas J. Jech: Set Theory 3rd Edition (1978) #2441  Kenneth Kunen: Set Theory (1980) #1881  P. R. Halmos: Naive Set Theory (1974) #1079 AA Fraenkel, Y Bar-Hillel, A Levy: Foundations of set theory (1973) #696 K Kuratowski, A Mostowski, M Mączyński: Set theory (1976) #609 Suppes: Axiomatic set theory  (1972) #589 Quine: Set theory and its logic (1969) #442 A Levy: Basic set theory (1979) #442 Herbert B. Enderton: Elements of Set Theory (1977) #349 Karel Hrbacek, Thomas J. Jech: Introduction to set theory (1999) #284 RR Stoll: Set theory and logic (1979) #281  N. Bourbaki: theory of sets (1970) #211 K Devlin: The joy of sets: fundamentals of contemporary set theory (1994) #182 Ciesielski: Set theory for the working mathematician (1997) #156 YN Moschovakis: Notes on set theory (1994) #138 FW Lawvere: Sets for mathematics (2003) #118 G Takeuti, WM Zaring: Introduction to axiomatic set theory (1982) #106 Kaplansky: Set Theory and Metric Spaces (2001) #103 Potter: Set Theory and Its Philosophy: A Critical Introduction (2004) #91 PT Johnstone: Notes on logic and set theory (1987) #87 Judith Roitman: Introduction to Modern Set Theory (1990) #47 Derek Goldrei: Set Theory: For Guided Independent Study (1996) #31 Basic set theory: A Shen, NK Vereshchagin (2002) #14 Ralf Schindler: Set Theory (2014) #13 Foreman, Kanamori: Handbook of Set Theory (2009) #38   Note:  Please feel free to add textbooks to the list, as long as they are not just on a smaller subset of set theory. (Some of the dates might not be the first published edition.) I remember reading a time travel book when I was young, which means it would have been written no later than the '80s, but probably much before that.  It featured an adult and some kids back in time and them trying to get back to the present.  I recall that the time travel effect was a ring, as at one point the ring opened up and a "brontosaurus" hit it and burned it's leg sending chunks of it back through the ring.  I recall a section where they were with "cave people" who had just hunted and killed some animal, and they used their pocket knife to extract more meat from the carcass, and actually cooking the meat unlike their paleolithic 'friends'.  (I seem to recall that one of the paleolithic girls seemed to fancy the boy time traveler, much to his discomfort.)  I am pretty sure that at one point they were watching the time ring appear over water, knowing they could not reach it, and waiting for it to be reachable.  I think the close of the book was them freezing to death in the ice age, commenting on how in the future when their bodies are found how it would be hard to explain how they got there, and then finally being rescued before it was too late.  I hope that's enough to go on?  Any ideas? From time to time certain chat rooms (JavaScript and probably PHP, too) attract the attention of a fellow help vampire who thinks he can start sucking from the people in there.  Often their message end up being flagged as offensive (and those flags are likely to be validated, too, because people are annoyed by such behaviour) but it's kind of an inappropriate use of those flags.  I'm proposing a new chat flag type, which is especially meant for help vampires. Flagging it would present the flag to 10k users and owners of the room where the flag originated (no matter how much rep they have). When the flag is validated it would cause messages from this user to be shown with a low opacity for maybe three hours. It could also notify the user that help vampirism is a bad thing and that he needs to improve his behaviour.  Repeated flags of this type - obviously with some time in between in case multiple message which are really part of the same conversation are flagged - should then result in a temporary ban from the room where the messages got flagged. If that doesn't help the next step would probably be a temporary ban from all chat rooms.    For clarification, I'm not talking about the quick "this line doesn't work, why?" stuff but the kind of help vampires who get cocky even though they just got e.g. a link to a SO question which has a perfectly fine and fitting answer. Because hey, you didn't give them teh codez! Show/Hide CSS Ignored When Inside an SLDS Grid Column Evaluation of Differentiation and Integration I was having some thought about what would be the syntax to make the end point evaluation of derivatives or integrals. Such as making the | with the two end points of evaluation on the top an bottom of the line. Any suggestions would be wonderful. Ignore folders/files when Directory.GetFiles() is denied access I am trying to display a list of all files found in the selected directory (and optionally any subdirectories). The problem I am having is that when the GetFiles() method comes across a folder that it cannot access, it throws an exception and the process stops.  How do I ignore this exception (and ignore the protected folder/file) and continue adding accessible files to the list?  try {     if (cbSubFolders.Checked == false)     {         string[] files = Directory.GetFiles(folderBrowserDialog1.SelectedPath);         foreach (string fileName in files)             ProcessFile(fileName);     }     else     {         string[] files = Directory.GetFiles(folderBrowserDialog1.SelectedPath, "*.*", SearchOption.AllDirectories);         foreach (string fileName in files)             ProcessFile(fileName);     }     lblNumberOfFilesDisplay.Enabled = true; } catch (UnauthorizedAccessException) { } finally {} Find objects between two dates MongoDB How might the weight of a falling object affect the damage it causes? Fall damage is 1d6 per 10 feet. What adjustments if any should I make for objects falling on a player character? (e.g. a bear)  Assuming the objects are meaningful threats but not instant character death, should the weight of an object change the calculation, e.g. more then 1d6 per 10 feet.  Or is this more in the spirit of improvising damage chart? i.e. the setback (cat to face) dangerous (orc fell on me), and deadly (the large bear).  If this is house-rule territory does any one have any experience or advice beyond  relevant to 5e. How to use fakeslant as slanted but not italic font with fontspec? Using fontspec with Luatex it is possible to create a fake slant and use that as italic should no italics be around:  \setmainfont[ AutoFakeSlant=0.15 ]             {FontName}   However, also if an italic version exist this faked slant will be used both for \itshape and \slshape. How can I keep using the shipped italic font defined by the ItalicFont= parameter to \setmainfont but use fake slant for \slshape? I used osm2pgsql to import data into my PostgreSQL database and it put gave me the following 4 tables, planet_osm_point, planet_osm_line, planet_osm_polygon and planet_osm_roads.   I have looked at the schema for osm2pgsql and inside the planet_osm_point table there is a column 'way' of type point. I tried to query it as an array like it says in the documentation here ():     It is possible to access the two component numbers of a point as   though the point were an array with indexes 0 and 1. For example, if   t.p is a point column then SELECT p[0] FROM t retrieves the X   coordinate and UPDATE t SET p[1] = ... changes the Y coordinate. In   the same way, a value of type box or lseg can be treated as an array   of two point values.   Anyone know the correct query the planet_osm tables from osm2pgsql based on long/lat? For example if I wanted to retrieve the information for Big Ben (London) I would query along the lines of:      SELECT * FROM planet_osm_point      WHERE ST_Y(ST_Transform(way, 4326)) = '-0.12'        AND ST_X(ST_Transform(way, 4326)) = '51.5';   There is no error message, it comes out with the table names, but no data is output either. (Its an empty table). What am I doing wrong here?  Perhaps it is too precise, i.e. there are no coordinates that match it exactly? Perhaps I need to try being more general, say 51 &lt; long &lt; 52 and -0.5 &lt; lat &lt; 0. Although this would throw back multiple results so would not be quite as accurate. finding the index of a max value in R Distribution of linear combination of OLS regression coefficients Getting Started With Java EE I am about to start a web project and have been working almost exclusively with a LAMP stack for the past 5 years.  I would like to build something larger and more scalable and hence have been looking into Java EE.  The division of logic between JSP and EJB seems ideal for what I want to do.  Can anyone recommend resources for getting familiar with Java EE?  And perhaps if anyone knows of technologies that are more scalable than PHP that I should consider as well, I'm all ears.  Thanks a lot! Permissions problems with /var/www/html and my own home directory for a website document root I'm trying to not give 777 permission in my /var/www/html folder, but I want to edit my files without sudo. So I though in create a symlink of a folder in my home directory within /var/www/html. I created it using sudo ln -sT /home/andre/www/moodle/ moodle , and the ls -la output is this:  andre@andre-270E5G:/var/www/html$ ls -la total 8 drwxr-xr-x 2 root root 4096 Mai  4 10:20 . drwxr-xr-x 4 root root 4096 Abr 29 14:29 .. lrwxrwxrwx 1 root root   23 Mai  4 10:20 moodle -&gt; /home/andre/www/moodle/   So, my moodle folder has read, write and execute permissions for everyone, and thats not what I want. I used the command sudo chmod -R 775 moodle/ trying to change it, but it stayed with read, write and execute permissions to all. I tried the same with the moodle folder in /home/andre/www/moodle, but it stayed the same. The output of ls -la in /home/andre/www/ is:  andre@andre-270E5G:~/www$ ls -la total 28 drwxrwxr-x  3 andre andre  4096 Mai  4 10:02 . drwx------ 49 andre andre 20480 Mai  4 10:01 .. drwxrwxr-x 41 andre andre  4096 Mai  4 10:02 moodle   So the folder moodle in /home/andre/www/ has the permissions I want.  As an additional problem, when I access localhost/moodle I get 403 Forbidden error.  What am I doing wrong here? How to retrieve checkboxes values in jQuery Is casting the same thing as converting? In Jesse Liberty's Learning C# book, he says "Objects of one type can be converted into objects of another type. This is called casting."  If you investigate the IL generated from the code below, you can clearly see that the casted assignment isn't doing the same thing as the converted assignment. In the former, you can see the boxing/unboxing occurring; in the latter you can see a call to a convert method.   I know in the end it may be just a silly  semantic difference--but is casting just another word for converting. I don't mean to be snarky, but I'm not interested in anyone's gut feeling on this--opinions don't count here! Can anyone point to a definitive reference that confirms or denies if casting and converting are the same thing?      object x;     int y;      x = 4;      y = ( int )x;      y = Convert.ToInt32( x );   Thank you  rp  Note added after Matt's comment about explicit/implicit:  I don't think implicit/explicit is the difference. In the code I posted, the change is explicit in both cases. An implicit conversion is what occurs when you assign a short to an int.  Note to Sklivvz:  I wanted confirmation that my suspicion of the looseness of Jesse Liberty's (otherwise usually lucid and clear) language was correct. I thought that Jesse Liberty was being a little loose with his language. I understand that casting is routed in object hierarchy--i.e., you can't cast from an integer to a string but you could cast from custom exception derived from System.Exception to a System.Exception.   It's interesting, though, that when you do try to cast from an int to a string the compiler tells you that it couldn't "convert" the value. Maybe Jesse is more correct than I thought! How do I make sure that values from MySQL keep their type in PHP?