This needs to be reprinted vs. this needs reprinted
"Needs cleaned" or "needs to be cleaned"
Matrix is conjugate to its own transpose Mariano mentioned somewhere that everyone should prove once in their life that every matrix is conjugate to its transpose.  I spent quite a bit of time on it now, and still could not prove it. At the risk of devaluing myself, might I ask someone else to show me a proof? Do Bard and Rogue expertise stack? If you multiclass correctly so you get expertise from both bard and rogue(e.g. Rogue 1 and Bard 3), and if in both classes you put the expertise into Deception, does it stack on an ability check?   Example:   The bard/rogue is proficient in Deception.  With a 16 (+3) charisma at level 4 would the character get a +15 bonus to Deception rolls? Why was Dumbledore worried by the cut in Harry's arm? In the Goblet of Fire, Harry is cut in the arm by Pettigrew. When Dumbledore learns it, he's extremely worried and wants to check Harry's arm.  Why?     When Harry told of Wormtail piercing his arm with the dagger, however, Sirius let out a vehement exclamation and Dumbledore stood up so quickly that Harry   started. Dumbledore walked around the desk and told Harry to stretch out his arm.   Harry showed them both the place where his robes were torn and the cut beneath   them.      "He said my blood would make him stronger than if he'd used someone else's,"   Harry told Dumbledore. "He said the protection my - my mother left in me - he'd   have it too. And he was right - he could touch me without hurting himself, he   touched my face."      For a fleeting instant, Harry thought he saw a gleam of something like triumph in   Dumbledore's eyes. But next second. Harry was sure he had imagined it, for when   Dumbledore had returned to his seat behind the desk, he looked as old and weary   as Harry had ever seen him.      "Very well," he said, sitting down again. "Voldemort has overcome that particular   barrier. Harry, continue, please.     Edit:  Plz explain this sentence specifically:     "Dumbledore walked around the desk and told Harry to stretch out his   arm." Exam with 18pt main font the slash (/) after a directory name on shell commands I have a little question here.  If I have two files, say filea and fileb, mv filea fileb would   delete fileb rename filea to fileb   Then if I have two directories, say dira and dirb, mv dira dirb would   move dira into dirb (it will become dirb/dira)   Noting that in both cases there are no notice or message, then this is pretty inconsistent to me. I think mv dira dirb should just overwrite dirb with the contents of dira (or merge the two directories under a directory named dirb).  I remember reading somewhere that a directory name with a slash (like dira/) is treated like a directory, and name with no slash (like dira) is treated like a file (to certain extents, of course). Anyway now I want to make the shell (zsh and possibly bash) respect my notation of a directory by using a slash. Is there a terminal option which enable me to enforce that?  To clarify, here is my desired behaviour:   mv dira dirb results in dirb being overwritten with the contents of dira mv dira dirb/ results in dira being moved into dirb (in dirb/dira)   Has anyone thought the same way as me? Or am I just weird? Expected number of rolling a pair of dice to generate all possible sums A pair of dice is rolled repeatedly until each outcome (2 through 12) has occurred at least once. What is the expected number of rolls necessary for this to occur?  Notes: This is not very deep conceptually, but because of the unequal probabilities for the outcomes, it seems that the calculations involved are terribly messy.  It must have been done already (dice have been studied for centuries!) but I can't find a discussion in any book, or on line. Can anybody give a reference? Attorney at law, is there any other kind? I have wondered from time to time about the phrase "attorney at law." Are there other kinds of attorneys? Attorneys at arms? If not, why do we specify? Can an abstract class have a constructor? Can an abstract class have a constructor?  If so, how can it be used and for what purposes? How can I reduce the ever-increasing time to push a subtree? Fit a table into one page Catch multiple exceptions at once? Undercooked beans in chili? I made a bit of a mistake, being a lazy bachelor and inexperienced at cooking.  I was making chili and when it came time to add beans I discovered I didn't have any canned beans.  I did however have some dried beans.  I decided to save time and add these directly to the pot of chili and add some water.  However, after much simmering the beans maintain a certain unpalatable crispness.  I have also read that undercooked beans contain a chemical lectin which can cause stomach discomfort.  I have also read that beans should be soaked, the water discarded to remove the lectin, and then boiled to cook them.  Is there any way to salvage this?  Should I just continue cooking the chili for hours?  Will I have to throw out my potentially delicious chili? What developer text editors are available for Ubuntu? How to disable pylint 'Undefined variable' error for a specific variable in a file? Java Strings: "String s = new String("silly");" I'm a C++ guy learning Java. I'm reading Effective Java and something confused me. It says never to write code like this:  String s = new String("silly");   Because it creates unnecessary String objects. But instead it should be written like this:  String s = "No longer silly";   Ok fine so far...However, given this class:  public final class CaseInsensitiveString {     private String s;     public CaseInsensitiveString(String s) {         if (s == null) {             throw new NullPointerException();         }         this.s = s;     }     :     : }  CaseInsensitiveString cis = new CaseInsensitiveString("Polish"); String s = "polish";    Why is the first statement ok? Shouldn't it be   CaseInsensitiveString cis = "Polish"; How do I make CaseInsensitiveString behave like String so the above statement is OK (with and without extending String)? What is it about String that makes it OK to just be able to pass it a literal like that? From my understanding there is no "copy constructor" concept in Java? Is the localization of a PID a PID? Let $A$ be a commutative ring and $S$ a multiplicative closed subset of $A$. If $A$ is a PID, show that $S^{-1}A$ is a PID.   I've taken an ideal $I$ of $S^{-1}A$ and I've tried to see that is generated by one element; the ideal $I$ has the form $S^{-1}J$ with $J$ an ideal of $A$. $J$ is generated by one element but I can't see why $I$ has to be generated by one element, maybe I'm wrong. I am confused with the grammar here. Which is grammatically correct?       At which time will you call me?     At what time will you call me?    And why? How can I create light trails without a blurry subject? Summation of series $\sum_{n=1}^\infty \frac{n^a}{b^n}$? How can we evaluate this series  $$\sum_{n=1}^\infty \frac{n^a}{b^n}?$$  Here $a$ and $b$ are positive integers. If $b=1$ then series will be diverging, in other cases, it will be converging, but how to find this sum?  Isn't there a simple solution which doesn't involve Stirling numbers? Fibonacci combinatorial identity: $F_{2n} = {n \choose 0} F_0 + {n\choose 1} F_1 + ... {n\choose n} F_n$ Can someone explain how to prove the following identity involving Fibonacci sequence  $F_n$  $F_{2n} = {n \choose 0} F_0 + {n\choose 1} F_1 + ... {n\choose n} F_n$ ?